Merge pull request 'Various features for example pipeline' (#31) from feat/complete-example into main

Reviewed-on: #31

docs/manual.typ

@@ -46,9 +46,9 @@ What this means is that in Python, type checks are deferred to runtime when oper
 For developers, it might seem like a great way of simplifying the language and making it very flexible, but it does come with a cost.
 Indeed, type errors are very easy to make in Python. While passing an integer where a string is expected might not be an issue in some cases, these are the sort of thing that can cause crashes or incorrect results without a clear diagnostic to help the user fix it.
 
-Fortunately, developers using IDEs or properly configured text editors can benefit from external type checkers such as MyPy which will perform static type analysis of their Python code. Some can also be configured to be very strict, forcing the user to make the whole code typable statically, thus avoiding any runtime type errors.
+Fortunately, developers using IDEs or properly configured text editors can benefit from external type checkers such as MyPy which will perform static type analysis of their Python code. Some can also be configured to be very strict, forcing the user to make the whole code typeable statically, thus avoiding any runtime type errors.
 
-This is not the end of the problem though. Some parts of a program, especially in data related fields, may not be available at "compile-time". For example, a dataset can be loaded from an external file, or data can be fetched from an API, with no guarantees of having the expected format when analysing the code statically.
+This is not the end of the problem though. Some parts of a program, especially in data related fields, may not be available at "compile-time". For example, a dataset can be loaded from an external file, or data can be fetched from an API, with no guarantees of having the expected format when analyzing the code statically.
 
 In turn, that can cause a range of loud and silent errors at runtime. A malformed number will probably crash the program when trying to convert it, but a NaN in a series of value might just produce wrong results without any exception. Combine this with often long-running data-processing pipelines and this is how developers can waste hours of precious computation time.
 
@@ -198,10 +198,26 @@ python3 build/midas/script.py
 In this chapter, you will find a complete reference for the Midas definition language.
 
 A `*.midas` file contains a number of statements, which can be:
+- *`alias`* statements (see @alias-stmt): to define a new type alias
 - *`type`* statements (see @type-stmt): to define a new type
 - *`extend`* statements (see @extend-stmt): to define member of a type
 - *`predicate`* statements (see @predicate-stmt): to define named predicates that can be used in constraint types
 
+== Alias Statement <alias-stmt>
+
+An *`alias`* statement lets you define a new type alias. It requires a unique name and base type.
+
+While a `type` statement (see @type-stmt) allows generic definitions, aliases are purely a for givin an alternative name to a type.
+
+#figure(
+  ```midas
+  alias MyType = float
+  ```,
+  caption: [Simple `alias` statement declaring a new type "`MyType`" equivalent to `float`],
+) <midas-simple-alias>
+
+This statement defines a new type called `MyType` which is equivalent to `float`. `MyType` and `float` can be used interchangeably.
+
 == Type Statement <type-stmt>
 
 A *`type`* statement lets you define a new type. It requires a unique name and base type.
@@ -212,7 +228,7 @@ The simplest form of a *`type`* statement is:
   type MyType = float
   ```,
   caption: [Simple `type` statement declaring a new type "`MyType`" as a subtype of `float`],
-) <midas-simple-alias>
+) <midas-simple-type>
 
 This statement defines a new type called `MyType` which is a subtype of `float`. `MyType` is a `float` but a `float` is not necessarily `MyType`.
 
@@ -291,8 +307,7 @@ To better refine a generic type, you can also bound type parameters using the fo
   caption: [Generic container type definition with a bound],
 )
 
-This can be read as "`Container` is a generic type which takes one type parameter `T` that must be a subtype of `float`".
-
+This can be read as "`Container` is a generic type which takes one type parameter `T` that must be a subtype of `float`".\
 You can use a generic type, i.e. instantiate it, by using a similar syntax with concrete type as arguments:
 
 #figure(
@@ -318,6 +333,46 @@ The _body_ of a generic type, i.e. the right-hand side of the definition, can co
   caption: [Type parameters in a generic type's body],
 )
 
+=== `Column` / `Frame` types
+
+To provide useful type-checking for data engineers, Midas offers two special types: `Column` and `Frame`.
+Their goal is to help type check Pandas' `Series` and `DataFrame` respectively.
+
+==== `Column`
+
+The `Column` type is a generic type used to represent a `pandas.Series` object.
+You can use it like any other generic type and it will provide type checking for some common methods and attributes offered by Pandas.
+
+#figure(
+  ```midas
+  type Temperature = float
+  alias Temperatures = Column[Temperature]
+  ```,
+  caption: [Simple column type definition],
+)
+
+==== `Frame` <frame-type>
+
+The `Frame` type is a super-powered generic type used to represent a `pandas.DataFrame` object.
+In place of type arguments, `Frame` accepts a schema, i.e. a series of column definitions.
+@simple-frame show how you can define a simple frame type with 3 columns:
+- `name`: a column of `Name` values
+- `age`: a column of `int` values
+- `height`: a column of `float where _ >= 0` values
+
+Notice that you don't need to specify `Column` types.
+
+#figure(
+  ```midas
+  type Name = str where len(_) != 0
+  alias Data = Frame[
+    name: Name,
+    age: int,
+    height: float where _ >= 0
+  ]
+  ```,
+) <simple-frame>
+
 #pagebreak()
 
 == Extend Statement <extend-stmt>
@@ -503,6 +558,7 @@ A simple annotation declaration, without assigning a value, is enough to declare
 )
 
 Because unpacking is not supported, assigning to multiple values is also not handled by the type checker.
+For more information about type annotations, see @type-annotations
 
 == Arithmetic
 
@@ -578,7 +634,7 @@ Conditional statements are checked relatively strictly by Midas. The test expres
 
 Simple forms of `for` loops can be used, that is using a single variable and iterating over an object implementing the `__getitem__` method. Like above in @if-else, leaking variables from inside the loop is ignored.
 
-The `for`-`else` statements are not supported. `while` loops are also not not supported.
+`for`-`else` statements are not supported. `while` loops are also not supported.
 
 == Functions
 
@@ -678,10 +734,43 @@ In the following example, a runtime check would be generated to ensure that the
   caption: [Typing of `cast` expression],
 )
 
+#gc.warning[
+  Assertions are statements inserted just before a statement using a `cast` expression. This means that the expression is evaluated _before_ its actual intended usage location, which might cause issues if you rely on logical operator short-circuiting. See @eager-eval for more information.
+]
+
 There may be some cases where the cost of checking a value at runtime is simply not worth the safety, for example when dealing with a big dataset. If do wish so, you can use `unsafe_cast` which will only tell the type checker the type of the value, without generating a runtime assertion. This maps to the default behavior of `typing`'s own `cast` function.
 
 If the value passed to `cast` or `unsafe_cast` is a literal (e.g. an integer, a string, a list of literals, etc.), the assertion is evaluated _at compile-time_ and no runtime assertion is generated.
 
+== Annotations / Type Hints <type-annotations>
+
+Vanilla Python already lets you use type hints to specify the type of variables and function parameters.
+
+Midas use them to type check your code. Additionally, it allows you to use a special syntax to define a `Frame` types directly in these annotations.
+
+Because these annotations are not interpretable by Python, your integrated type checker might complain loudly about them being invalid.
+A workaround is to silence it by adding a type comment at the end of the line, as shown in @silence-errors.
+
+#figure(
+  ```python
+  var: Frame[name: str, age: float]  # type: ignore # noqa: F821
+  ```,
+  caption: [MyPy's and Pylance's complaints about custom type annotation can be silenced with type comments],
+) <silence-errors>
+
+=== Frame type annotation
+
+The syntax is similar to how you can define frame types in the Midas language (see @frame-type). The only difference is that types can only be name references; you cannot inline constraint types.
+
+The example of @python-frame-type shows how you can annotate a dataframe with some columns directly in Python.
+
+#figure(
+  ```python
+  df: Frame[name: Name, age: float, height: Length[Meter]] = ...
+  ```,
+  caption: [Frame type annotation in Python],
+) <python-frame-type>
+
 = Commands <commands>
 
 #TODO
@@ -695,3 +784,26 @@ If the value passed to `cast` or `unsafe_cast` is a literal (e.g. an integer, a
 == Generating Stubs (`stubs`) <cmd-stubs>
 == Showing Type Judgements (`types`) <cmd-types>
 == Validating Definitions (`validate`) <cmd-validate>
+
+= Known limitations <limitations>
+
+== Eager evaluation in runtime assertions <eager-eval>
+
+The process of generating assertions to ensure safety at runtime, mainly for `cast` expressions, leads to the creation of aliases for the expressions being casted. These alias definitions eagerly evaluate before the assertion, and most importantly before the real usage location. This means that you should avoid using `cast` expressions inside logical expressions like `and` or `or`, because the normal "short-circuit" behavior will be irrelevant to the evaluations of the operands.
+
+For example:
+
+#figure(
+  ```py
+  def foo():
+      print("Foo")
+      return True
+  def bar():
+      print("Bar")
+      return True
+  result = foo() or bar()
+  # Foo
+  # Bar
+  ```,
+  caption: [Runtime assertions may eagerly evaluate expressions and bypass logical operator's short-circuit],
+)

docs/midas.sublime-syntax

@@ -9,8 +9,10 @@ variables:
   identifier: "[a-zA-Z_][a-zA-Z0-9_]*"
 
 contexts:
-  main:
+  prototype:
     - include: comments
+
+  main:
     - include: keywords
     - include: types
 
@@ -28,7 +30,16 @@ contexts:
         - match: \*/
           pop: true
 
+  string:
+    - meta_include_prototype: false
+    - meta_scope: string.quoted.double.c
+    - match: '"'
+      pop: true
+
   keywords:
+    - match: \balias\b
+      scope: keyword.declaration.midas
+      push: alias-stmt
     - match: \btype\b
       scope: keyword.declaration.midas
       push: type-stmt
@@ -39,8 +50,16 @@ contexts:
       scope: keyword.declaration.midas
       push: predicate-stmt
 
+  alias-stmt:
+    - match: "{{identifier}}"
+      scope: entity.name.type
+    - match: "="
+      scope: keyword.operator.equal.midas
+      push: type-expr
+    - match: $
+      pop: true
+
   type-stmt:
-    - include: comments
     - match: "{{identifier}}"
       scope: entity.name.type
     - match: \[
@@ -52,7 +71,6 @@ contexts:
       pop: true
 
   type-expr:
-    - include: comments
     - match: \b(fn)\s*(\()
       captures:
         1: keyword.other.midas
@@ -61,6 +79,13 @@ contexts:
     - match: \b(where)\b
       scope: keyword.other.midas
       set: constraint
+    - match: "Frame"
+      scope: entity.name.type
+      push:
+        - match: \[
+          push: frame-schema
+        - match: $
+          pop: true
     - match: "{{identifier}}"
       scope: entity.name.type
     - match: $
@@ -88,7 +113,6 @@ contexts:
           set: type-expr
 
   constraint:
-    - include: comments
     - match: $
       pop: 2
 
@@ -98,6 +122,9 @@ contexts:
     - match: \b(true|false|none)\b
       scope: constant.language.midas
 
+    - match: '"'
+      push: string
+
     - match: (<=|>=|<|>|==|!=|&)
       scope: keyword.operator
 
@@ -111,7 +138,6 @@ contexts:
       scope: variable.other.readwrite.midas
 
   type-params:
-    - include: comments
     - match: "<:"
       scope: keyword.operator.subtype.midas
     - match: "[a-zA-Z][a-zA-Z_0-9]*"
@@ -120,21 +146,19 @@ contexts:
       pop: true
 
   extend-stmt:
-    - include: comments
     - match: "{{identifier}}"
       scope: entity.name.type
     - match: \[
       push: type-params
     - match: \{
       scope: punctuation.section.block.begin
-      push: extend-body
+      set: extend-body
 
   extend-body:
-    - include: comments
     - include: member-stmt
     - match: \}
       scope: punctuation.section.block.end
-      pop: 2
+      pop: true
 
   member-stmt:
     - match: \b(prop|def)\b
@@ -148,7 +172,6 @@ contexts:
           pop: true
 
   predicate-stmt:
-    - include: comments
     - match: "{{identifier}}"
       scope: entity.name.function.midas
     - match: '\('
@@ -174,3 +197,15 @@ contexts:
 
     - match: '\)'
       pop: true
+
+  frame-schema:
+    - include: frame-column
+    - match: \]
+      # scope: punctuation.section.block.end
+      pop: true
+
+  frame-column:
+    - match: "{{identifier}}"
+      scope: variable.other.member
+    - match: ":"
+      push: type-expr

examples/02_demonstration/weather/custom_types.midas

@@ -0,0 +1,65 @@
+predicate in_range(min: float, max: float)(v: float) = min <= v & v <= max
+predicate is_percentage = in_range(0.0, 100.0)
+
+type Celsius = float
+type Kelvin = float where _ >= 0
+type Hectopascal = float
+
+type Temperature = Celsius where in_range(-30.0, 100.0)
+type Pressure = Hectopascal where in_range(800.0, 1100.0)(_)
+type Humidity = float where is_percentage(_)
+type HeatIndex = float
+
+type StationID = str where len(_) == 3 & _.isupper()
+
+type Mean[T <: float] = float
+
+extend Celsius {
+    def __add__: fn(Celsius, /) -> Celsius
+    def __sub__: fn(Celsius, /) -> Celsius
+}
+
+extend Kelvin {
+    def __add__: fn(Kelvin, /) -> Kelvin
+}
+
+extend Hectopascal {
+    def __add__: fn(Hectopascal, /) -> Hectopascal
+    def __sub__: fn(Hectopascal, /) -> Hectopascal
+}
+
+alias RawData = Frame[
+    station_id: str,
+    timestamp: str,
+    temperature: float,
+    pressure: float,
+    humidity: float,
+]
+
+alias Data = Frame[
+    station_id: StationID,
+    timestamp: object,
+    temperature: Temperature,
+    pressure: Pressure,
+    humidity: Humidity,
+]
+
+alias DataWithHI = Frame[
+    station_id: StationID,
+    timestamp: object,
+    temperature: Temperature,
+    pressure: Pressure,
+    humidity: Humidity,
+    heat_index: HeatIndex,
+]
+
+alias DailyAverages = Frame[
+    timestamp: object,
+    temperature: Mean[Temperature],
+    pressure: Mean[Pressure],
+    humidity: Mean[Humidity],
+    heat_index: Mean[HeatIndex],
+]
+
+predicate limit_amplitude(max_amp: float)(ls: list[float]) = max(ls) - min(ls) <= max_amp
+type LowAmplitudeWave = list[float where _ >= 1] where limit_amplitude(10)(_)

examples/02_demonstration/weather/gen_data.py

@@ -0,0 +1,43 @@
+import datetime
+import random
+
+import pandas as pd
+
+stations = ["SIO", "AIG", "ZER"]
+
+start_ts = datetime.datetime(2026, 1, 1)
+end_ts = datetime.datetime(2027, 1, 1)
+delta = end_ts - start_ts
+
+min_temp, max_temp = -30.0, 100.0
+min_pres, max_pres = 800.0, 1100.0
+min_hum, max_hum = 0.0, 1.0
+
+N = 3000
+
+rows: list[tuple[str, datetime.datetime, float, float, float]] = []
+
+for _ in range(N):
+    ts = random.random() * delta + start_ts
+    rows.append(
+        (
+            random.choice(stations),
+            ts,
+            random.random() * (max_temp - min_temp) + min_temp,
+            random.random() * (max_pres - min_pres) + min_pres,
+            random.random() * (max_hum - min_hum) + min_hum,
+        )
+    )
+
+df = pd.DataFrame(
+    rows,
+    columns=[
+        "station_id",
+        "timestamp",
+        "temperature",
+        "pressure",
+        "humidity",
+    ],
+)
+df = df.sort_values(by=["timestamp", "station_id"])
+df.to_csv("data.csv", index=False)

examples/02_demonstration/weather/pipeline.py

@@ -0,0 +1,81 @@
+from pathlib import Path
+
+import matplotlib.pyplot as plt
+import pandas as pd
+from custom_types import DailyAverages, Data, DataWithHI, HeatIndex, RawData
+
+from midas.typing import Column, cast, unsafe_cast
+
+
+def load_data(path: Path) -> RawData:
+    # Check base types and dataframe structure
+    return cast(RawData, pd.read_csv(path))
+
+
+def convert_data(raw_df: RawData) -> Data:
+    new_df = raw_df.copy()
+    new_df["timestamp"] = cast(
+        Column[object],
+        pd.to_datetime(new_df["timestamp"]),
+    )
+
+    # Check types and constraints at runtime, catches out-of-range values and
+    # invalid types / malformed data
+    return cast(Data, new_df)
+
+
+def compute_heat_index(df: Data):
+    # The computation's result can only be typed as `Column[float]`
+    # Casting is necessary to bring back semantic
+    df["heat_index"] = cast(
+        Column[HeatIndex],
+        (
+            df["temperature"] * 2.0
+            + df["humidity"] * 10.0
+            - df["temperature"] * df["humidity"] * 0.2
+        ),
+    )
+    return df
+
+
+def daily_avg(df: DataWithHI):
+    # Group-by and aggregation methods keep the structure of the dataframe but
+    # may erase the exact types
+    # The type checker is still very conservative and often the result of most
+    # aggregation methods as `Column[Any]`
+    return cast(
+        DailyAverages,
+        df.groupby(
+            by=[
+                df["station_id"],
+                df["timestamp"].dt.day.rename("day"),
+            ],
+        )
+        .mean()
+        .sort_values(by="timestamp"),
+    )
+
+
+def plot(df: DailyAverages):
+    # Some operations are not implemented in Midas but the user can still use
+    # them, they will just not be fully type-checked
+    # `unsafe_cast` can also be used to avoid trivial, redundant or costly checks
+    stations = unsafe_cast(list[str], list(df.index.get_level_values(0).unique()))
+    for station in stations:
+        sub_df = unsafe_cast(DailyAverages, df.loc[station])
+        plt.plot(sub_df["timestamp"], sub_df["heat_index"])
+    plt.show()
+
+
+def main():
+    # Assigning to annotated variables help catch errors
+    raw_df: RawData = load_data(Path("data.csv"))
+    df: Data = convert_data(raw_df)
+
+    with_hi = compute_heat_index(df)
+    dailies = daily_avg(with_hi)
+    plot(dailies)
+
+
+if __name__ == "__main__":
+    main()

gen/gen.py

@@ -1,3 +1,9 @@
+"""
+Helper script to generate AST nodes for Midas and Python.
+
+Takes in simple templates and generates full dataclasses and a visitor interface
+"""
+
 import re
 from pathlib import Path
 

gen/midas.py

@@ -29,9 +29,9 @@ class MemberKind(Enum):
 @dataclass(frozen=True, kw_only=True)
 class ParamSpec:
     l_paren: Token
-    pos: list[FunctionType.Argument]
-    mixed: list[FunctionType.Argument]
-    kw: list[FunctionType.Argument]
+    pos: list[FunctionType.Parameter]
+    mixed: list[FunctionType.Parameter]
+    kw: list[FunctionType.Parameter]
 
 
 ###<
@@ -44,6 +44,11 @@ class TypeStmt:
     type: Type
 
 
+class AliasStmt:
+    name: Token
+    type: Type
+
+
 class MemberStmt:
     name: Token
     type: Type
@@ -145,11 +150,21 @@ class FunctionType:
     returns: Type
 
     @dataclass(frozen=True, kw_only=True)
-    class Argument:
+    class Parameter:
         location: Optional[Location] = None
         name: Optional[Token]
         type: Type
         required: bool
 
 
+class FrameType:
+    columns: list[Column]
+
+    @dataclass(frozen=True, kw_only=True)
+    class Column:
+        location: Optional[Location] = None
+        name: Token
+        type: Type
+
+
 ###<

gen/python.py

@@ -12,10 +12,36 @@ from midas.ast.location import Location
 ###<
 
 
+###> Preamble
+@dataclass(frozen=True, kw_only=True)
+class ParamSpec:
+    pos: list[Function.Parameter]
+    mixed: list[Function.Parameter]
+    kw: list[Function.Parameter]
+
+    @property
+    def all(self) -> list[Function.Parameter]:
+        return self.pos + self.mixed + self.kw
+
+
+@dataclass(frozen=True, kw_only=True)
+class ImportAlias:
+    location: Location
+    name: str
+    alias: Optional[str] = None
+
+    @property
+    def imported_name(self) -> str:
+        return self.alias if self.alias is not None else self.name
+
+
+###<
+
+
 ###> MidasType | Type annotations | node
 class BaseType:
     base: str
-    param: Optional[MidasType]
+    args: tuple[MidasType, ...]
 
 
 class ConstraintType:
@@ -42,25 +68,17 @@ class ExpressionStmt:
 
 class Function:
     name: str
-    posonlyargs: list[Argument]
-    args: list[Argument]
-    sink: Optional[Argument]
-    kwonlyargs: list[Argument]
-    kw_sink: Optional[Argument]
+    params: ParamSpec
     returns: Optional[MidasType]
     body: list[Stmt]
 
     @dataclass(frozen=True, kw_only=True)
-    class Argument:
+    class Parameter:
         location: Optional[Location] = None
         name: str
         type: Optional[MidasType]
         default: Optional[Expr]
 
-    @property
-    def all_args(self) -> list[Argument]:
-        return self.posonlyargs + self.args + self.kwonlyargs
-
 
 class TypeAssign:
     name: str
@@ -92,6 +110,16 @@ class ForStmt:
     body: list[Stmt]
 
 
+class ImportStmt:
+    imports: list[ImportAlias]
+
+
+class FromImportStmt:
+    module: Optional[str]
+    imports: list[ImportAlias]
+    level: int
+
+
 class RawStmt:
     stmt: ast.stmt
 
@@ -174,6 +202,10 @@ class SliceExpr:
     step: Optional[Expr]
 
 
+class TupleExpr:
+    items: tuple[Expr, ...]
+
+
 class RawExpr:
     expr: ast.expr
 

midas/ast/location.py

@@ -13,6 +13,8 @@ class HasLocation(Protocol):
 
 @dataclass(frozen=True, kw_only=True)
 class Location:
+    """Information about the location of an AST node"""
+
     lineno: int
     col_offset: int
     end_lineno: Optional[int]
@@ -29,6 +31,16 @@ class Location:
 
     @staticmethod
     def span(start: Location, end: Location) -> Location:
+        """Create a new location spanning from one location to another
+
+        Args:
+            start (Location): the starting location
+            end (Location): the end location
+
+        Returns:
+            Location: a new location spanning from the start of `start`
+                to the end of `end`
+        """
         return Location(
             lineno=start.lineno,
             col_offset=start.col_offset,

midas/ast/midas.py

@@ -30,9 +30,9 @@ class MemberKind(Enum):
 @dataclass(frozen=True, kw_only=True)
 class ParamSpec:
     l_paren: Token
-    pos: list[FunctionType.Argument]
-    mixed: list[FunctionType.Argument]
-    kw: list[FunctionType.Argument]
+    pos: list[FunctionType.Parameter]
+    mixed: list[FunctionType.Parameter]
+    kw: list[FunctionType.Parameter]
 
 
 ##############
@@ -51,6 +51,9 @@ class Stmt(ABC):
         @abstractmethod
         def visit_type_stmt(self, stmt: TypeStmt) -> T: ...
 
+        @abstractmethod
+        def visit_alias_stmt(self, stmt: AliasStmt) -> T: ...
+
         @abstractmethod
         def visit_member_stmt(self, stmt: MemberStmt) -> T: ...
 
@@ -71,6 +74,15 @@ class TypeStmt(Stmt):
         return visitor.visit_type_stmt(self)
 
 
+@dataclass(frozen=True)
+class AliasStmt(Stmt):
+    name: Token
+    type: Type
+
+    def accept(self, visitor: Stmt.Visitor[T]) -> T:
+        return visitor.visit_alias_stmt(self)
+
+
 @dataclass(frozen=True)
 class MemberStmt(Stmt):
     name: Token
@@ -253,6 +265,9 @@ class Type(ABC):
         @abstractmethod
         def visit_function_type(self, type: FunctionType) -> T: ...
 
+        @abstractmethod
+        def visit_frame_type(self, type: FrameType) -> T: ...
+
 
 @dataclass(frozen=True)
 class NamedType(Type):
@@ -303,7 +318,7 @@ class FunctionType(Type):
     returns: Type
 
     @dataclass(frozen=True, kw_only=True)
-    class Argument:
+    class Parameter:
         location: Optional[Location] = None
         name: Optional[Token]
         type: Type
@@ -311,3 +326,17 @@ class FunctionType(Type):
 
     def accept(self, visitor: Type.Visitor[T]) -> T:
         return visitor.visit_function_type(self)
+
+
+@dataclass(frozen=True)
+class FrameType(Type):
+    columns: list[Column]
+
+    @dataclass(frozen=True, kw_only=True)
+    class Column:
+        location: Optional[Location] = None
+        name: Token
+        type: Type
+
+    def accept(self, visitor: Type.Visitor[T]) -> T:
+        return visitor.visit_frame_type(self)

midas/ast/printer.py

@@ -1,832 +0,0 @@
-from __future__ import annotations
-
-import ast
-import io
-from contextlib import contextmanager
-from enum import Enum, auto
-from typing import Generator, Generic, Optional, Protocol, TypeVar
-
-import midas.ast.midas as m
-import midas.ast.python as p
-
-
-class _Level(Enum):
-    EMPTY = auto()
-    ACTIVE = auto()
-    LAST = auto()
-
-
-class Expr(Protocol):
-    def accept(self, printer: AstPrinter) -> None: ...
-
-
-T = TypeVar("T", bound=Expr)
-
-
-class AstPrinter(Generic[T]):
-    LAST_CHILD = "└── "
-    CHILD = "├── "
-    VERTICAL = "│   "
-    EMPTY = "    "
-
-    def __init__(self):
-        self._levels: list[_Level] = []
-        self._idx: Optional[int] = None
-        self._buf: io.StringIO = io.StringIO()
-
-    def print(self, expr: T):
-        self._buf = io.StringIO()
-        expr.accept(self)
-        return self._buf.getvalue()
-
-    @contextmanager
-    def _child_level(self, single: bool = False) -> Generator[None, None, None]:
-        self._levels.append(_Level.LAST if single else _Level.ACTIVE)
-        try:
-            yield
-        finally:
-            self._levels.pop()
-
-    def _mark_last(self):
-        if self._levels:
-            self._levels[-1] = _Level.LAST
-
-    def _write_line(self, text: str, *, last: bool = False):
-        if last:
-            self._mark_last()
-        indent: str = self._build_indent()
-        if self._idx is not None:
-            text = f"[{self._idx}] {text}"
-            self._idx = None
-        self._buf.write(indent + text + "\n")
-
-    def _build_indent(self) -> str:
-        parts: list[str] = []
-        for level in self._levels[:-1]:
-            parts.append(self.EMPTY if level == _Level.EMPTY else self.VERTICAL)
-        if self._levels:
-            if self._levels[-1] == _Level.LAST:
-                parts.append(self.LAST_CHILD)
-                self._levels[-1] = _Level.EMPTY
-            else:
-                parts.append(self.CHILD)
-        return "".join(parts)
-
-    def _write_optional_child(
-        self, label: str, child: Optional[T], *, last: bool = False
-    ):
-        if last:
-            self._mark_last()
-        if child is None:
-            self._write_line(f"{label}: None")
-        else:
-            self._write_line(label)
-            with self._child_level(single=True):
-                child.accept(self)
-
-
-class MidasAstPrinter(
-    AstPrinter, m.Expr.Visitor[None], m.Stmt.Visitor[None], m.Type.Visitor[None]
-):
-    # Statements
-
-    def visit_type_stmt(self, stmt: m.TypeStmt) -> None:
-        self._write_line("TypeStmt")
-        with self._child_level():
-            self._write_line(f'name: "{stmt.name.lexeme}"')
-            self._write_line("params")
-            with self._child_level():
-                for i, param in enumerate(stmt.params):
-                    self._idx = i
-                    if i == len(stmt.params) - 1:
-                        self._mark_last()
-                    self._print_type_param(param)
-            self._write_line("type", last=True)
-            with self._child_level(single=True):
-                stmt.type.accept(self)
-
-    def _print_type_param(self, param: m.TypeParam) -> None:
-        self._write_line("Param")
-        with self._child_level():
-            self._write_line(f'name: "{param.name.lexeme}"')
-            self._write_optional_child("bound", param.bound, last=True)
-
-    def visit_member_stmt(self, stmt: m.MemberStmt):
-        self._write_line("MemberStmt")
-        with self._child_level():
-            self._write_line(f"kind: {stmt.kind.name}")
-            self._write_line(f'name: "{stmt.name.lexeme}"')
-            self._write_line("type", last=True)
-            with self._child_level(single=True):
-                stmt.type.accept(self)
-
-    def visit_extend_stmt(self, stmt: m.ExtendStmt) -> None:
-        self._write_line("ExtendStmt")
-        with self._child_level():
-            self._write_line("params")
-            with self._child_level():
-                for i, param in enumerate(stmt.params):
-                    self._idx = i
-                    if i == len(stmt.params) - 1:
-                        self._mark_last()
-                    self._print_type_param(param)
-            self._write_line(f'name: "{stmt.name.lexeme}"')
-            self._write_line("params")
-            with self._child_level():
-                for i, param in enumerate(stmt.params):
-                    self._idx = i
-                    if i == len(stmt.params) - 1:
-                        self._mark_last()
-                    self._print_type_param(param)
-            self._write_line("members", last=True)
-            with self._child_level():
-                for i, member in enumerate(stmt.members):
-                    self._idx = i
-                    if i == len(stmt.members) - 1:
-                        self._mark_last()
-                    member.accept(self)
-
-    def visit_predicate_stmt(self, stmt: m.PredicateStmt):
-        self._write_line("PredicateStmt")
-        with self._child_level():
-            self._write_line(f'name: "{stmt.name.lexeme}"')
-            self._write_line("params")
-            with self._child_level():
-                for i, spec in enumerate(stmt.params):
-                    self._idx = i
-                    if i == len(stmt.params) - 1:
-                        self._mark_last()
-                    self._visit_param_spec(spec)
-
-            self._write_line("body", last=True)
-            with self._child_level(single=True):
-                stmt.body.accept(self)
-
-    # Expressions
-
-    def visit_logical_expr(self, expr: m.LogicalExpr):
-        self._write_line("LogicalExpr")
-        with self._child_level():
-            self._write_line("left")
-            with self._child_level(single=True):
-                expr.left.accept(self)
-
-            self._write_line(f"operator: {expr.operator.lexeme}")
-
-            self._write_line("right", last=True)
-            with self._child_level(single=True):
-                expr.right.accept(self)
-
-    def visit_binary_expr(self, expr: m.BinaryExpr):
-        self._write_line("BinaryExpr")
-        with self._child_level():
-            self._write_line("left")
-            with self._child_level(single=True):
-                expr.left.accept(self)
-
-            self._write_line(f"operator: {expr.operator.lexeme}")
-
-            self._write_line("right", last=True)
-            with self._child_level(single=True):
-                expr.right.accept(self)
-
-    def visit_unary_expr(self, expr: m.UnaryExpr):
-        self._write_line("UnaryExpr")
-        with self._child_level():
-            self._write_line(f"operator: {expr.operator.lexeme}")
-
-            self._write_line("right", last=True)
-            with self._child_level(single=True):
-                expr.right.accept(self)
-
-    def visit_call_expr(self, expr: m.CallExpr) -> None:
-        self._write_line("CallExpr")
-        with self._child_level():
-            self._write_line("callee")
-            with self._child_level(single=True):
-                expr.callee.accept(self)
-            self._write_line("arguments")
-            with self._child_level():
-                for i, arg in enumerate(expr.arguments):
-                    self._idx = i
-                    if i == len(expr.arguments) - 1:
-                        self._mark_last()
-                    arg.accept(self)
-            self._write_line("keywords", last=True)
-            with self._child_level():
-                for i, (name, arg) in enumerate(expr.keywords.items()):
-                    self._idx = i
-                    if i == len(expr.keywords) - 1:
-                        self._mark_last()
-                    self._write_line(name)
-                    with self._child_level(single=True):
-                        arg.accept(self)
-
-    def visit_get_expr(self, expr: m.GetExpr):
-        self._write_line("GetExpr")
-        with self._child_level():
-            self._write_line("expr")
-            with self._child_level(single=True):
-                expr.expr.accept(self)
-            self._write_line(f'name: "{expr.name.lexeme}"', last=True)
-
-    def visit_variable_expr(self, expr: m.VariableExpr):
-        self._write_line("VariableExpr")
-        with self._child_level():
-            self._write_line(f'name: "{expr.name.lexeme}"', last=True)
-
-    def visit_grouping_expr(self, expr: m.GroupingExpr):
-        self._write_line("GroupingExpr")
-        with self._child_level():
-            self._write_line("expr", last=True)
-            with self._child_level(single=True):
-                expr.expr.accept(self)
-
-    def visit_literal_expr(self, expr: m.LiteralExpr) -> None:
-        self._write_line("LiteralExpr")
-        with self._child_level():
-            self._write_line(f"value: {expr.value}", last=True)
-
-    def visit_wildcard_expr(self, expr: m.WildcardExpr) -> None:
-        self._write_line("WildcardExpr")
-
-    def visit_named_type(self, type: m.NamedType) -> None:
-        self._write_line("NamedType")
-        with self._child_level():
-            self._write_line(f'name: "{type.name.lexeme}"', last=True)
-
-    def visit_generic_type(self, type: m.GenericType) -> None:
-        self._write_line("GenericType")
-        with self._child_level():
-            self._write_line("type")
-            with self._child_level():
-                type.type.accept(self)
-            self._write_line("args", last=True)
-            with self._child_level():
-                for i, param in enumerate(type.args):
-                    self._idx = i
-                    if i == len(type.args) - 1:
-                        self._mark_last()
-                    param.accept(self)
-
-    def visit_constraint_type(self, type: m.ConstraintType) -> None:
-        self._write_line("ConstraintType")
-        with self._child_level():
-            self._write_line("type")
-            with self._child_level(single=True):
-                type.type.accept(self)
-            self._write_line("constraint", last=True)
-            with self._child_level(single=True):
-                type.constraint.accept(self)
-
-    def visit_complex_type(self, type: m.ComplexType) -> None:
-        self._write_line("ComplexType")
-        with self._child_level():
-            self._write_line("members", last=True)
-            with self._child_level():
-                for i, member in enumerate(type.members):
-                    self._idx = i
-                    if i == len(type.members) - 1:
-                        self._mark_last()
-                    member.accept(self)
-
-    def visit_extension_type(self, type: m.ExtensionType) -> None:
-        self._write_line("ExtensionType")
-        with self._child_level():
-            self._write_line("base")
-            with self._child_level(single=True):
-                type.base.accept(self)
-            self._write_line("extension", last=True)
-            with self._child_level(single=True):
-                type.extension.accept(self)
-
-    def visit_function_type(self, type: m.FunctionType) -> None:
-        self._write_line("FunctionType")
-        with self._child_level():
-            self._write_line("params")
-            with self._child_level(single=True):
-                self._visit_param_spec(type.params)
-
-            self._write_line("returns", last=True)
-            with self._child_level(single=True):
-                type.returns.accept(self)
-
-    def _visit_param_spec(self, spec: m.ParamSpec) -> None:
-        self._write_line("ParamSpec")
-        with self._child_level():
-            self._write_line("pos")
-            with self._child_level():
-                for i, arg in enumerate(spec.pos):
-                    self._idx = i
-                    if i == len(spec.pos) - 1:
-                        self._mark_last()
-                    self._print_function_arg(arg)
-
-            self._write_line("mixed")
-            with self._child_level():
-                for i, arg in enumerate(spec.mixed):
-                    self._idx = i
-                    if i == len(spec.mixed) - 1:
-                        self._mark_last()
-                    self._print_function_arg(arg)
-
-            self._write_line("kw", last=True)
-            with self._child_level():
-                for i, arg in enumerate(spec.kw):
-                    self._idx = i
-                    if i == len(spec.kw) - 1:
-                        self._mark_last()
-                    self._print_function_arg(arg)
-
-    def _print_function_arg(self, arg: m.FunctionType.Argument) -> None:
-        self._write_line("Argument")
-        with self._child_level():
-            name: str = "None"
-            if arg.name is not None:
-                name = f'"{arg.name.lexeme}"'
-            self._write_line(f"name: {name}")
-            self._write_line("type")
-            with self._child_level(single=True):
-                arg.type.accept(self)
-            self._write_line(f"required: {arg.required}", last=True)
-
-
-class MidasPrinter(m.Expr.Visitor[str], m.Stmt.Visitor[str], m.Type.Visitor[str]):
-    def __init__(self, indent: int = 4):
-        self.indent: int = indent
-        self.level: int = 0
-
-    def indented(self, text: str) -> str:
-        return " " * (self.level * self.indent) + text
-
-    def print(self, expr: m.Expr | m.Stmt | m.Type) -> str:
-        self.level = 0
-        return expr.accept(self)
-
-    def visit_type_stmt(self, stmt: m.TypeStmt) -> str:
-        template: str = ""
-        if len(stmt.params) != 0:
-            params: list[str] = [self._print_type_param(param) for param in stmt.params]
-            template = f"[{', '.join(params)}]"
-        res: str = f"type {stmt.name.lexeme}{template} = {stmt.type.accept(self)}"
-        return self.indented(res)
-
-    def _print_type_param(self, param: m.TypeParam) -> str:
-        res: str = param.name.lexeme
-        if param.bound is not None:
-            res += "<:" + param.bound.accept(self)
-        return res
-
-    def visit_member_stmt(self, stmt: m.MemberStmt):
-        keyword: str = {
-            m.MemberKind.PROPERTY: "prop",
-            m.MemberKind.METHOD: "def",
-        }.get(stmt.kind, "")
-        res: str = f"{keyword} {stmt.name.lexeme}: {stmt.type.accept(self)}"
-        return self.indented(res)
-
-    def visit_extend_stmt(self, stmt: m.ExtendStmt):
-        template: str = ""
-        if len(stmt.params) != 0:
-            params: list[str] = [self._print_type_param(param) for param in stmt.params]
-            template = f"[{', '.join(params)}]"
-        res: str = self.indented(f"extend {stmt.name.lexeme}{template}")
-        res += " {\n"
-        self.level += 1
-        for member in stmt.members:
-            res += member.accept(self) + "\n"
-        self.level -= 1
-        res += self.indented("}")
-        return res
-
-    def visit_predicate_stmt(self, stmt: m.PredicateStmt):
-        name: str = stmt.name.lexeme
-        sig: str = "".join(self._visit_param_spec(spec) for spec in stmt.params)
-        body: str = stmt.body.accept(self)
-        return self.indented(f"predicate {name}{sig} = {body}")
-
-    def visit_logical_expr(self, expr: m.LogicalExpr):
-        left: str = expr.left.accept(self)
-        operator: str = expr.operator.lexeme
-        right: str = expr.right.accept(self)
-        return f"{left} {operator} {right}"
-
-    def visit_binary_expr(self, expr: m.BinaryExpr):
-        left: str = expr.left.accept(self)
-        operator: str = expr.operator.lexeme
-        right: str = expr.right.accept(self)
-        return f"{left} {operator} {right}"
-
-    def visit_unary_expr(self, expr: m.UnaryExpr):
-        operator: str = expr.operator.lexeme
-        right: str = expr.right.accept(self)
-        return f"{operator}{right}"
-
-    def visit_call_expr(self, expr: m.CallExpr) -> str:
-        args: list[str] = [arg.accept(self) for arg in expr.arguments] + [
-            f"{name}={arg.accept(self)}" for name, arg in expr.keywords.items()
-        ]
-        return f"{expr.callee.accept(self)}({', '.join(args)})"
-
-    def visit_get_expr(self, expr: m.GetExpr):
-        expr_: str = expr.expr.accept(self)
-        name: str = expr.name.lexeme
-        return f"{expr_}.{name}"
-
-    def visit_variable_expr(self, expr: m.VariableExpr):
-        return expr.name.lexeme
-
-    def visit_grouping_expr(self, expr: m.GroupingExpr):
-        expr_: str = expr.expr.accept(self)
-        return f"({expr_})"
-
-    def visit_literal_expr(self, expr: m.LiteralExpr):
-        return str(expr.value)
-
-    def visit_wildcard_expr(self, expr: m.WildcardExpr):
-        return "_"
-
-    def visit_named_type(self, type: m.NamedType) -> str:
-        return type.name.lexeme
-
-    def visit_generic_type(self, type: m.GenericType) -> str:
-        res: str = type.type.accept(self)
-        if len(type.args) != 0:
-            args: list[str] = [param.accept(self) for param in type.args]
-            res += f"[{', '.join(args)}]"
-        return res
-
-    def visit_constraint_type(self, type: m.ConstraintType) -> str:
-        res: str = type.type.accept(self)
-        res += " where " + type.constraint.accept(self)
-        return res
-
-    def visit_complex_type(self, type: m.ComplexType) -> str:
-        res: str = "{\n"
-        self.level += 1
-        for member in type.members:
-            res += member.accept(self)
-            res += "\n"
-        self.level -= 1
-        res += self.indented("}")
-        return res
-
-    def visit_extension_type(self, type: m.ExtensionType) -> str:
-        return f"{type.base.accept(self)} & {type.extension.accept(self)}"
-
-    def visit_function_type(self, type: m.FunctionType) -> str:
-        spec: str = self._visit_param_spec(type.params)
-        return f"fn {spec} -> {type.returns.accept(self)}"
-
-    def _visit_param_spec(self, spec: m.ParamSpec) -> str:
-        pos_args: list[str] = [self._print_arg(arg) for arg in spec.pos]
-        mixed_args: list[str] = [self._print_arg(arg) for arg in spec.mixed]
-        kw_args: list[str] = [self._print_arg(arg) for arg in spec.kw]
-        args: list[str] = pos_args
-
-        if len(pos_args) != 0:
-            args.append("/")
-        args += mixed_args
-        if len(kw_args) != 0:
-            args.append("*")
-        args += kw_args
-        return f"({', '.join(args)})"
-
-    def _print_arg(self, arg: m.FunctionType.Argument) -> str:
-        res: str = ""
-        if arg.name is not None:
-            res += arg.name.lexeme
-            res += ": "
-        res += arg.type.accept(self)
-        if not arg.required:
-            res += "?"
-        return res
-
-
-class PythonAstPrinter(
-    AstPrinter,
-    p.MidasType.Visitor[None],
-    p.Stmt.Visitor[None],
-    p.Expr.Visitor[None],
-):
-    def visit_base_type(self, node: p.BaseType) -> None:
-        self._write_line("BaseType")
-        with self._child_level():
-            self._write_line(f"base: {node.base}")
-            self._write_optional_child("param", node.param, last=True)
-
-    def visit_constraint_type(self, node: p.ConstraintType) -> None:
-        self._write_line("ConstraintType")
-        with self._child_level():
-            self._write_line("type")
-            with self._child_level(single=True):
-                node.type.accept(self)
-            self._write_line(f"constraint: {ast.unparse(node.constraint)}", last=True)
-
-    def visit_frame_column(self, node: p.FrameColumn) -> None:
-        self._write_line("FrameColumn")
-        with self._child_level():
-            self._write_line(f"name: {node.name}")
-            self._write_optional_child("type", node.type, last=True)
-
-    def visit_frame_type(self, node: p.FrameType) -> None:
-        self._write_line("FrameType")
-        with self._child_level():
-            self._write_line("columns", last=True)
-            with self._child_level():
-                for i, col in enumerate(node.columns):
-                    self._idx = i
-                    if i == len(node.columns) - 1:
-                        self._mark_last()
-                    col.accept(self)
-
-    def visit_expression_stmt(self, stmt: p.ExpressionStmt) -> None:
-        stmt.expr.accept(self)
-
-    def visit_function(self, stmt: p.Function) -> None:
-        self._write_line("Function")
-        with self._child_level():
-            self._write_line(f"name: {stmt.name}")
-
-            self._write_line("posonlyargs")
-            with self._child_level():
-                for i, arg in enumerate(stmt.posonlyargs):
-                    self._idx = i
-                    if i == len(stmt.posonlyargs) - 1:
-                        self._mark_last()
-                    self._print_argument(arg)
-
-            self._write_line("args")
-            with self._child_level():
-                for i, arg in enumerate(stmt.args):
-                    self._idx = i
-                    if i == len(stmt.args) - 1:
-                        self._mark_last()
-                    self._print_argument(arg)
-
-            self._write_line("kwonlyargs")
-            with self._child_level():
-                for i, arg in enumerate(stmt.kwonlyargs):
-                    self._idx = i
-                    if i == len(stmt.kwonlyargs) - 1:
-                        self._mark_last()
-                    self._print_argument(arg)
-
-            self._write_optional_child("returns", stmt.returns)
-            self._write_line("body", last=True)
-            with self._child_level():
-                for i, body_stmt in enumerate(stmt.body):
-                    self._idx = i
-                    if i == len(stmt.body) - 1:
-                        self._mark_last()
-                    body_stmt.accept(self)
-
-    def _print_argument(self, arg: p.Function.Argument) -> None:
-        self._write_line("FunctionArgument")
-        with self._child_level():
-            self._write_line(f"name: {arg.name}")
-            self._write_optional_child("type", arg.type, last=True)
-
-    def visit_type_assign(self, stmt: p.TypeAssign) -> None:
-        self._write_line("TypeAssign")
-        with self._child_level():
-            self._write_line(f"name: {stmt.name}")
-            self._write_line("type", last=True)
-            with self._child_level(single=True):
-                stmt.type.accept(self)
-
-    def visit_assign_stmt(self, stmt: p.AssignStmt) -> None:
-        self._write_line("AssignStmt")
-        with self._child_level():
-            self._write_line("targets")
-            with self._child_level():
-                for i, target in enumerate(stmt.targets):
-                    self._idx = i
-                    if i == len(stmt.targets) - 1:
-                        self._mark_last()
-                    target.accept(self)
-            self._write_line("value", last=True)
-            with self._child_level(single=True):
-                stmt.value.accept(self)
-
-    def visit_return_stmt(self, stmt: p.ReturnStmt) -> None:
-        self._write_line("ReturnStmt")
-        with self._child_level():
-            self._write_optional_child("value", stmt.value, last=True)
-
-    def visit_if_stmt(self, stmt: p.IfStmt) -> None:
-        self._write_line("IfStmt")
-        with self._child_level():
-            self._write_line("test")
-            with self._child_level(single=True):
-                stmt.test.accept(self)
-            self._write_line("body")
-            with self._child_level():
-                for i, body_stmt in enumerate(stmt.body):
-                    self._idx = i
-                    if i == len(stmt.body) - 1:
-                        self._mark_last()
-                    body_stmt.accept(self)
-            self._write_line("orelse", last=True)
-            with self._child_level():
-                for i, else_stmt in enumerate(stmt.orelse):
-                    self._idx = i
-                    if i == len(stmt.orelse) - 1:
-                        self._mark_last()
-                    else_stmt.accept(self)
-
-    def visit_pass(self, stmt: p.Pass) -> None:
-        self._write_line("Pass")
-
-    def visit_for_stmt(self, stmt: p.ForStmt) -> None:
-        self._write_line("ForStmt")
-        with self._child_level():
-            self._write_line("target")
-            with self._child_level(single=True):
-                stmt.target.accept(self)
-            self._write_line("iterator")
-            with self._child_level(single=True):
-                stmt.iterator.accept(self)
-            self._write_line("body", last=True)
-            with self._child_level():
-                for i, body_stmt in enumerate(stmt.body):
-                    self._idx = i
-                    if i == len(stmt.body) - 1:
-                        self._mark_last()
-                    body_stmt.accept(self)
-
-    def visit_raw_stmt(self, stmt: p.RawStmt) -> None:
-        self._write_line("RawStmt")
-        with self._child_level(single=True):
-            self._write_line(f"stmt: {ast.unparse(stmt.stmt)}")
-
-    def visit_binary_expr(self, expr: p.BinaryExpr) -> None:
-        self._write_line("BinaryExpr")
-        with self._child_level():
-            self._write_line("left")
-            with self._child_level(single=True):
-                expr.left.accept(self)
-
-            self._write_line(f"operator: {expr.operator.__class__.__name__}")
-
-            self._write_line("right", last=True)
-            with self._child_level(single=True):
-                expr.right.accept(self)
-
-    def visit_compare_expr(self, expr: p.CompareExpr) -> None:
-        self._write_line("CompareExpr")
-        with self._child_level():
-            self._write_line("left")
-            with self._child_level(single=True):
-                expr.left.accept(self)
-
-            self._write_line(f"operator: {expr.operator.__class__.__name__}")
-
-            self._write_line("right", last=True)
-            with self._child_level(single=True):
-                expr.right.accept(self)
-
-    def visit_unary_expr(self, expr: p.UnaryExpr) -> None:
-        self._write_line("UnaryExpr")
-        with self._child_level():
-            self._write_line(f"operator: {expr.operator.__class__.__name__}")
-
-            self._write_line("right", last=True)
-            with self._child_level(single=True):
-                expr.right.accept(self)
-
-    def visit_call_expr(self, expr: p.CallExpr) -> None:
-        self._write_line("CallExpr")
-        with self._child_level():
-            self._write_line("callee")
-            with self._child_level(single=True):
-                expr.callee.accept(self)
-
-            self._write_line("arguments")
-            with self._child_level():
-                for i, arg in enumerate(expr.arguments):
-                    self._idx = i
-                    if i == len(expr.arguments) - 1:
-                        self._mark_last()
-                    arg.accept(self)
-
-            self._write_line("keywords", last=True)
-            with self._child_level():
-                for i, (name, arg) in enumerate(expr.keywords.items()):
-                    self._idx = i
-                    if i == len(expr.keywords) - 1:
-                        self._mark_last()
-                    self._write_line(name)
-                    with self._child_level(single=True):
-                        arg.accept(self)
-
-    def visit_get_expr(self, expr: p.GetExpr) -> None:
-        self._write_line("GetExpr")
-        with self._child_level():
-            self._write_line("object")
-            with self._child_level(single=True):
-                expr.object.accept(self)
-            self._write_line(f"name: {expr.name}", last=True)
-
-    def visit_literal_expr(self, expr: p.LiteralExpr) -> None:
-        self._write_line("LiteralExpr")
-        with self._child_level(single=True):
-            self._write_line(f"value: {expr.value!r}")
-
-    def visit_variable_expr(self, expr: p.VariableExpr) -> None:
-        self._write_line("VariableExpr")
-        with self._child_level(single=True):
-            self._write_line(f"name: {expr.name}")
-
-    def visit_logical_expr(self, expr: p.LogicalExpr) -> None:
-        self._write_line("LogicalExpr")
-        with self._child_level():
-            self._write_line("left")
-            with self._child_level(single=True):
-                expr.left.accept(self)
-
-            self._write_line(f"operator: {expr.operator.__class__.__name__}")
-
-            self._write_line("right", last=True)
-            with self._child_level(single=True):
-                expr.right.accept(self)
-
-    def visit_cast_expr(self, expr: p.CastExpr) -> None:
-        self._write_line("CastExpr")
-        with self._child_level():
-            self._write_line("type")
-            with self._child_level(single=True):
-                expr.type.accept(self)
-            self._write_line("expr")
-            with self._child_level(single=True):
-                expr.expr.accept(self)
-            self._write_line(f"unsafe: {expr.unsafe}", last=True)
-
-    def visit_ternary_expr(self, expr: p.TernaryExpr) -> None:
-        self._write_line("TernaryExpr")
-        with self._child_level():
-            self._write_line("test")
-            with self._child_level(single=True):
-                expr.test.accept(self)
-
-            self._write_line("if_true")
-            with self._child_level(single=True):
-                expr.if_true.accept(self)
-
-            self._write_line("if_false", last=True)
-            with self._child_level(single=True):
-                expr.if_false.accept(self)
-
-    def visit_list_expr(self, expr: p.ListExpr) -> None:
-        self._write_line("ListExpr")
-        with self._child_level():
-            self._write_line("items", last=True)
-            with self._child_level():
-                for i, item in enumerate(expr.items):
-                    self._idx = i
-                    if i == len(expr.items) - 1:
-                        self._mark_last()
-                    item.accept(self)
-
-    def visit_dict_expr(self, expr: p.DictExpr) -> None:
-        self._write_line("DictExpr")
-        with self._child_level():
-            self._write_line("keys")
-            with self._child_level():
-                for i, key in enumerate(expr.keys):
-                    self._idx = i
-                    if i == len(expr.keys) - 1:
-                        self._mark_last()
-                    if key is None:
-                        self._write_line("None")
-                    else:
-                        key.accept(self)
-            self._write_line("values", last=True)
-            with self._child_level():
-                for i, value in enumerate(expr.values):
-                    self._idx = i
-                    if i == len(expr.values) - 1:
-                        self._mark_last()
-                    value.accept(self)
-
-    def visit_subscript_expr(self, expr: p.SubscriptExpr) -> None:
-        self._write_line("SubscriptExpr")
-        with self._child_level():
-            self._write_line("object")
-            with self._child_level(single=True):
-                expr.object.accept(self)
-            self._write_line("index", last=True)
-            with self._child_level(single=True):
-                expr.index.accept(self)
-
-    def visit_slice_expr(self, expr: p.SliceExpr) -> None:
-        self._write_line("SliceExpr")
-        with self._child_level():
-            self._write_optional_child("lower", expr.lower)
-            self._write_optional_child("upper", expr.upper)
-            self._write_optional_child("step", expr.step, last=True)
-
-    def visit_raw_expr(self, expr: p.RawExpr) -> None:
-        self._write_line("RawExpr")
-        with self._child_level(single=True):
-            self._write_line(f"expr: {ast.unparse(expr.expr)}")

midas/ast/printer/__init__.py

@@ -0,0 +1,3 @@
+from .midas import MidasPrinter as MidasPrinter
+from .midas_ast import MidasAstPrinter as MidasAstPrinter
+from .python_ast import PythonAstPrinter as PythonAstPrinter

midas/ast/printer/base.py

@@ -0,0 +1,103 @@
+from __future__ import annotations
+
+import io
+from contextlib import contextmanager
+from enum import Enum, auto
+from typing import Callable, Generator, Generic, Optional, Protocol, Sequence, TypeVar
+
+
+class _Level(Enum):
+    EMPTY = auto()
+    ACTIVE = auto()
+    LAST = auto()
+
+
+class Expr(Protocol):
+    def accept(self, printer: AstPrinter) -> None: ...
+
+
+T = TypeVar("T", bound=Expr)
+
+
+class AstPrinter(Generic[T]):
+    LAST_CHILD = "└── "
+    CHILD = "├── "
+    VERTICAL = "│   "
+    EMPTY = "    "
+
+    def __init__(self):
+        self._levels: list[_Level] = []
+        self._idx: Optional[int] = None
+        self._buf: io.StringIO = io.StringIO()
+
+    def print(self, expr: T):
+        self._buf = io.StringIO()
+        expr.accept(self)
+        return self._buf.getvalue()
+
+    @contextmanager
+    def _child_level(self, single: bool = False) -> Generator[None, None, None]:
+        self._levels.append(_Level.LAST if single else _Level.ACTIVE)
+        try:
+            yield
+        finally:
+            self._levels.pop()
+
+    def _mark_last(self):
+        if self._levels:
+            self._levels[-1] = _Level.LAST
+
+    def _write_line(self, text: str, *, last: bool = False):
+        if last:
+            self._mark_last()
+        indent: str = self._build_indent()
+        if self._idx is not None:
+            text = f"[{self._idx}] {text}"
+            self._idx = None
+        self._buf.write(indent + text + "\n")
+
+    def _build_indent(self) -> str:
+        parts: list[str] = []
+        for level in self._levels[:-1]:
+            parts.append(self.EMPTY if level == _Level.EMPTY else self.VERTICAL)
+        if self._levels:
+            if self._levels[-1] == _Level.LAST:
+                parts.append(self.LAST_CHILD)
+                self._levels[-1] = _Level.EMPTY
+            else:
+                parts.append(self.CHILD)
+        return "".join(parts)
+
+    def _write_optional_child(
+        self, label: str, child: Optional[T], *, last: bool = False
+    ):
+        if last:
+            self._mark_last()
+        if child is None:
+            self._write_line(f"{label}: None")
+        else:
+            self._write_line(label)
+            with self._child_level(single=True):
+                child.accept(self)
+
+    def _write_sequence(
+        self,
+        label: str,
+        list_: Sequence[T],
+        *,
+        last: bool = False,
+        print_func: Optional[Callable[[T], None]] = None,
+    ):
+        if last:
+            self._mark_last()
+
+        self._write_line(label)
+        with self._child_level():
+            for i, item in enumerate(list_):
+                self._idx = i
+                if i == len(list_) - 1:
+                    self._mark_last()
+                if print_func is not None:
+                    print_func(item)
+                else:
+                    item.accept(self)

midas/ast/printer/midas.py

@@ -0,0 +1,183 @@
+import midas.ast.midas as m
+
+
+class MidasPrinter(
+    m.Expr.Visitor[str],
+    m.Stmt.Visitor[str],
+    m.Type.Visitor[str],
+):
+    def __init__(self, indent: int = 4):
+        self.indent: int = indent
+        self.level: int = 0
+
+    def indented(self, text: str) -> str:
+        return " " * (self.level * self.indent) + text
+
+    def print(self, expr: m.Expr | m.Stmt | m.Type) -> str:
+        self.level = 0
+        return expr.accept(self)
+
+    # Statements
+
+    def visit_type_stmt(self, stmt: m.TypeStmt) -> str:
+        template: str = ""
+        if len(stmt.params) != 0:
+            params: list[str] = [self._print_type_param(param) for param in stmt.params]
+            template = f"[{', '.join(params)}]"
+        res: str = f"type {stmt.name.lexeme}{template} = {stmt.type.accept(self)}"
+        return self.indented(res)
+
+    def visit_alias_stmt(self, stmt: m.AliasStmt) -> str:
+        return self.indented(f"alias {stmt.name.lexeme} = {stmt.type.accept(self)}")
+
+    def _print_type_param(self, param: m.TypeParam) -> str:
+        res: str = param.name.lexeme
+        if param.bound is not None:
+            res += "<:" + param.bound.accept(self)
+        return res
+
+    def visit_member_stmt(self, stmt: m.MemberStmt):
+        keyword: str = {
+            m.MemberKind.PROPERTY: "prop",
+            m.MemberKind.METHOD: "def",
+        }.get(stmt.kind, "")
+        res: str = f"{keyword} {stmt.name.lexeme}: {stmt.type.accept(self)}"
+        return self.indented(res)
+
+    def visit_extend_stmt(self, stmt: m.ExtendStmt):
+        template: str = ""
+        if len(stmt.params) != 0:
+            params: list[str] = [self._print_type_param(param) for param in stmt.params]
+            template = f"[{', '.join(params)}]"
+        res: str = self.indented(f"extend {stmt.name.lexeme}{template}")
+        res += " {\n"
+        self.level += 1
+        for member in stmt.members:
+            res += member.accept(self) + "\n"
+        self.level -= 1
+        res += self.indented("}")
+        return res
+
+    def visit_predicate_stmt(self, stmt: m.PredicateStmt):
+        name: str = stmt.name.lexeme
+        sig: str = "".join(self._visit_param_spec(spec) for spec in stmt.params)
+        body: str = stmt.body.accept(self)
+        return self.indented(f"predicate {name}{sig} = {body}")
+
+    # Expressions
+
+    def visit_logical_expr(self, expr: m.LogicalExpr):
+        left: str = expr.left.accept(self)
+        operator: str = expr.operator.lexeme
+        right: str = expr.right.accept(self)
+        return f"{left} {operator} {right}"
+
+    def visit_binary_expr(self, expr: m.BinaryExpr):
+        left: str = expr.left.accept(self)
+        operator: str = expr.operator.lexeme
+        right: str = expr.right.accept(self)
+        return f"{left} {operator} {right}"
+
+    def visit_unary_expr(self, expr: m.UnaryExpr):
+        operator: str = expr.operator.lexeme
+        right: str = expr.right.accept(self)
+        return f"{operator}{right}"
+
+    def visit_call_expr(self, expr: m.CallExpr) -> str:
+        args: list[str] = [arg.accept(self) for arg in expr.arguments] + [
+            f"{name}={arg.accept(self)}" for name, arg in expr.keywords.items()
+        ]
+        return f"{expr.callee.accept(self)}({', '.join(args)})"
+
+    def visit_get_expr(self, expr: m.GetExpr):
+        expr_: str = expr.expr.accept(self)
+        name: str = expr.name.lexeme
+        return f"{expr_}.{name}"
+
+    def visit_variable_expr(self, expr: m.VariableExpr):
+        return expr.name.lexeme
+
+    def visit_grouping_expr(self, expr: m.GroupingExpr):
+        expr_: str = expr.expr.accept(self)
+        return f"({expr_})"
+
+    def visit_literal_expr(self, expr: m.LiteralExpr):
+        return str(expr.value)
+
+    def visit_wildcard_expr(self, expr: m.WildcardExpr):
+        return "_"
+
+    # Types
+
+    def visit_named_type(self, type: m.NamedType) -> str:
+        return type.name.lexeme
+
+    def visit_generic_type(self, type: m.GenericType) -> str:
+        res: str = type.type.accept(self)
+        if len(type.args) != 0:
+            args: list[str] = [param.accept(self) for param in type.args]
+            res += f"[{', '.join(args)}]"
+        return res
+
+    def visit_constraint_type(self, type: m.ConstraintType) -> str:
+        res: str = type.type.accept(self)
+        res += " where " + type.constraint.accept(self)
+        return res
+
+    def visit_complex_type(self, type: m.ComplexType) -> str:
+        res: str = "{\n"
+        self.level += 1
+        for member in type.members:
+            res += member.accept(self)
+            res += "\n"
+        self.level -= 1
+        res += self.indented("}")
+        return res
+
+    def visit_extension_type(self, type: m.ExtensionType) -> str:
+        return f"{type.base.accept(self)} & {type.extension.accept(self)}"
+
+    def visit_function_type(self, type: m.FunctionType) -> str:
+        spec: str = self._visit_param_spec(type.params)
+        return f"fn {spec} -> {type.returns.accept(self)}"
+
+    def _visit_param_spec(self, spec: m.ParamSpec) -> str:
+        pos: list[str] = [self._print_param(param) for param in spec.pos]
+        mixed: list[str] = [self._print_param(param) for param in spec.mixed]
+        kw: list[str] = [self._print_param(param) for param in spec.kw]
+        params: list[str] = pos
+
+        if len(pos) != 0:
+            params.append("/")
+        params += mixed
+        if len(kw) != 0:
+            params.append("*")
+        params += kw
+        return f"({', '.join(params)})"
+
+    def _print_param(self, param: m.FunctionType.Parameter) -> str:
+        res: str = ""
+        if param.name is not None:
+            res += param.name.lexeme
+            res += ": "
+        res += param.type.accept(self)
+        if not param.required:
+            res += "?"
+        return res
+
+    def visit_frame_type(self, type: m.FrameType) -> str:
+        res: str = self.indented("Frame[")
+        if len(type.columns) != 0:
+            res += "\n"
+            self.level += 1
+            columns: list[str] = []
+            for column in type.columns:
+                columns.append(self.indented(self._print_frame_column(column)))
+            res += ",\n".join(columns)
+            self.level -= 1
+            res += "\n"
+        res += "]"
+        return res
+
+    def _print_frame_column(self, column: m.FrameType.Column) -> str:
+        return f"{column.name.lexeme}: {column.type.accept(self)}"

midas/ast/printer/midas_ast.py

@@ -0,0 +1,253 @@
+import midas.ast.midas as m
+from midas.ast.printer.base import AstPrinter
+
+
+class MidasAstPrinter(
+    AstPrinter,
+    m.Expr.Visitor[None],
+    m.Stmt.Visitor[None],
+    m.Type.Visitor[None],
+):
+    # Statements
+
+    def visit_type_stmt(self, stmt: m.TypeStmt) -> None:
+        self._write_line("TypeStmt")
+        with self._child_level():
+            self._write_line(f'name: "{stmt.name.lexeme}"')
+            self._write_sequence(
+                "params",
+                stmt.params,
+                print_func=self._print_type_param,
+            )
+            self._write_line("type", last=True)
+            with self._child_level(single=True):
+                stmt.type.accept(self)
+
+    def visit_alias_stmt(self, stmt: m.AliasStmt) -> None:
+        self._write_line("AliasStmt")
+        with self._child_level():
+            self._write_line(f'name: "{stmt.name.lexeme}"')
+            self._write_line("type", last=True)
+            with self._child_level(single=True):
+                stmt.type.accept(self)
+
+    def _print_type_param(self, param: m.TypeParam) -> None:
+        self._write_line("Param")
+        with self._child_level():
+            self._write_line(f'name: "{param.name.lexeme}"')
+            self._write_optional_child("bound", param.bound, last=True)
+
+    def visit_member_stmt(self, stmt: m.MemberStmt):
+        self._write_line("MemberStmt")
+        with self._child_level():
+            self._write_line(f"kind: {stmt.kind.name}")
+            self._write_line(f'name: "{stmt.name.lexeme}"')
+            self._write_line("type", last=True)
+            with self._child_level(single=True):
+                stmt.type.accept(self)
+
+    def visit_extend_stmt(self, stmt: m.ExtendStmt) -> None:
+        self._write_line("ExtendStmt")
+        with self._child_level():
+            self._write_line(f'name: "{stmt.name.lexeme}"')
+            self._write_sequence(
+                "params",
+                stmt.params,
+                print_func=self._print_type_param,
+            )
+            self._write_sequence("members", stmt.members, last=True)
+
+    def visit_predicate_stmt(self, stmt: m.PredicateStmt):
+        self._write_line("PredicateStmt")
+        with self._child_level():
+            self._write_line(f'name: "{stmt.name.lexeme}"')
+            self._write_sequence(
+                "params",
+                stmt.params,
+                print_func=self._visit_param_spec,
+            )
+            self._write_line("body", last=True)
+            with self._child_level(single=True):
+                stmt.body.accept(self)
+
+    # Expressions
+
+    def visit_logical_expr(self, expr: m.LogicalExpr):
+        self._write_line("LogicalExpr")
+        with self._child_level():
+            self._write_line("left")
+            with self._child_level(single=True):
+                expr.left.accept(self)
+
+            self._write_line(f"operator: {expr.operator.lexeme}")
+
+            self._write_line("right", last=True)
+            with self._child_level(single=True):
+                expr.right.accept(self)
+
+    def visit_binary_expr(self, expr: m.BinaryExpr):
+        self._write_line("BinaryExpr")
+        with self._child_level():
+            self._write_line("left")
+            with self._child_level(single=True):
+                expr.left.accept(self)
+
+            self._write_line(f"operator: {expr.operator.lexeme}")
+
+            self._write_line("right", last=True)
+            with self._child_level(single=True):
+                expr.right.accept(self)
+
+    def visit_unary_expr(self, expr: m.UnaryExpr):
+        self._write_line("UnaryExpr")
+        with self._child_level():
+            self._write_line(f"operator: {expr.operator.lexeme}")
+
+            self._write_line("right", last=True)
+            with self._child_level(single=True):
+                expr.right.accept(self)
+
+    def visit_call_expr(self, expr: m.CallExpr) -> None:
+        self._write_line("CallExpr")
+        with self._child_level():
+            self._write_line("callee")
+            with self._child_level(single=True):
+                expr.callee.accept(self)
+            self._write_sequence("arguments", expr.arguments)
+            self._write_line("keywords", last=True)
+            with self._child_level():
+                for i, (name, arg) in enumerate(expr.keywords.items()):
+                    self._idx = i
+                    if i == len(expr.keywords) - 1:
+                        self._mark_last()
+                    self._write_line(name)
+                    with self._child_level(single=True):
+                        arg.accept(self)
+
+    def visit_get_expr(self, expr: m.GetExpr):
+        self._write_line("GetExpr")
+        with self._child_level():
+            self._write_line("expr")
+            with self._child_level(single=True):
+                expr.expr.accept(self)
+            self._write_line(f'name: "{expr.name.lexeme}"', last=True)
+
+    def visit_variable_expr(self, expr: m.VariableExpr):
+        self._write_line("VariableExpr")
+        with self._child_level():
+            self._write_line(f'name: "{expr.name.lexeme}"', last=True)
+
+    def visit_grouping_expr(self, expr: m.GroupingExpr):
+        self._write_line("GroupingExpr")
+        with self._child_level():
+            self._write_line("expr", last=True)
+            with self._child_level(single=True):
+                expr.expr.accept(self)
+
+    def visit_literal_expr(self, expr: m.LiteralExpr) -> None:
+        self._write_line("LiteralExpr")
+        with self._child_level():
+            self._write_line(f"value: {expr.value}", last=True)
+
+    def visit_wildcard_expr(self, expr: m.WildcardExpr) -> None:
+        self._write_line("WildcardExpr")
+
+    # Types
+
+    def visit_named_type(self, type: m.NamedType) -> None:
+        self._write_line("NamedType")
+        with self._child_level():
+            self._write_line(f'name: "{type.name.lexeme}"', last=True)
+
+    def visit_generic_type(self, type: m.GenericType) -> None:
+        self._write_line("GenericType")
+        with self._child_level():
+            self._write_line("type")
+            with self._child_level():
+                type.type.accept(self)
+            self._write_sequence("args", type.args, last=True)
+
+    def visit_constraint_type(self, type: m.ConstraintType) -> None:
+        self._write_line("ConstraintType")
+        with self._child_level():
+            self._write_line("type")
+            with self._child_level(single=True):
+                type.type.accept(self)
+            self._write_line("constraint", last=True)
+            with self._child_level(single=True):
+                type.constraint.accept(self)
+
+    def visit_complex_type(self, type: m.ComplexType) -> None:
+        self._write_line("ComplexType")
+        with self._child_level():
+            self._write_sequence("members", type.members, last=True)
+
+    def visit_extension_type(self, type: m.ExtensionType) -> None:
+        self._write_line("ExtensionType")
+        with self._child_level():
+            self._write_line("base")
+            with self._child_level(single=True):
+                type.base.accept(self)
+            self._write_line("extension", last=True)
+            with self._child_level(single=True):
+                type.extension.accept(self)
+
+    def visit_function_type(self, type: m.FunctionType) -> None:
+        self._write_line("FunctionType")
+        with self._child_level():
+            self._write_line("params")
+            with self._child_level(single=True):
+                self._visit_param_spec(type.params)
+
+            self._write_line("returns", last=True)
+            with self._child_level(single=True):
+                type.returns.accept(self)
+
+    def _visit_param_spec(self, spec: m.ParamSpec) -> None:
+        self._write_line("ParamSpec")
+        with self._child_level():
+            self._write_sequence(
+                "pos",
+                spec.pos,
+                print_func=self._print_param,
+            )
+            self._write_sequence(
+                "mixed",
+                spec.mixed,
+                print_func=self._print_param,
+            )
+            self._write_sequence(
+                "kw",
+                spec.kw,
+                print_func=self._print_param,
+                last=True,
+            )
+
+    def _print_param(self, param: m.FunctionType.Parameter) -> None:
+        self._write_line("Parameter")
+        with self._child_level():
+            name: str = "None"
+            if param.name is not None:
+                name = f'"{param.name.lexeme}"'
+            self._write_line(f"name: {name}")
+            self._write_line("type")
+            with self._child_level(single=True):
+                param.type.accept(self)
+            self._write_line(f"required: {param.required}", last=True)
+
+    def visit_frame_type(self, type: m.FrameType) -> None:
+        self._write_line("FrameType")
+        with self._child_level(single=True):
+            self._write_sequence(
+                "columns",
+                type.columns,
+                print_func=self._print_frame_column,
+            )
+
+    def _print_frame_column(self, column: m.FrameType.Column) -> None:
+        self._write_line("Column")
+        with self._child_level():
+            self._write_line(f'name: "{column.name.lexeme}"')
+            self._write_line("type")
+            with self._child_level(single=True):
+                column.type.accept(self)

midas/ast/printer/python_ast.py

@@ -0,0 +1,285 @@
+import ast
+
+import midas.ast.python as p
+from midas.ast.printer.base import AstPrinter
+
+
+class PythonAstPrinter(
+    AstPrinter,
+    p.MidasType.Visitor[None],
+    p.Stmt.Visitor[None],
+    p.Expr.Visitor[None],
+):
+    # Types
+
+    def visit_base_type(self, node: p.BaseType) -> None:
+        self._write_line("BaseType")
+        with self._child_level():
+            self._write_line(f"base: {node.base}")
+            self._write_sequence("args", node.args, last=True)
+
+    def visit_constraint_type(self, node: p.ConstraintType) -> None:
+        self._write_line("ConstraintType")
+        with self._child_level():
+            self._write_line("type")
+            with self._child_level(single=True):
+                node.type.accept(self)
+            self._write_line(f"constraint: {ast.unparse(node.constraint)}", last=True)
+
+    def visit_frame_column(self, node: p.FrameColumn) -> None:
+        self._write_line("FrameColumn")
+        with self._child_level():
+            self._write_line(f"name: {node.name}")
+            self._write_optional_child("type", node.type, last=True)
+
+    def visit_frame_type(self, node: p.FrameType) -> None:
+        self._write_line("FrameType")
+        with self._child_level(single=True):
+            self._write_sequence("columns", node.columns)
+
+    # Statements
+
+    def visit_expression_stmt(self, stmt: p.ExpressionStmt) -> None:
+        stmt.expr.accept(self)
+
+    def visit_function(self, stmt: p.Function) -> None:
+        self._write_line("Function")
+        with self._child_level():
+            self._write_line(f"name: {stmt.name}")
+            self._write_line("params")
+            with self._child_level():
+                self._print_param_spec(stmt.params)
+
+            self._write_optional_child("returns", stmt.returns)
+            self._write_sequence("body", stmt.body, last=True)
+
+    def _print_param_spec(self, spec: p.ParamSpec) -> None:
+        self._write_line("ParamSpec")
+        with self._child_level():
+            self._write_sequence(
+                "pos",
+                spec.pos,
+                print_func=self._print_param,
+            )
+            self._write_sequence(
+                "mixed",
+                spec.mixed,
+                print_func=self._print_param,
+            )
+            self._write_sequence(
+                "kw",
+                spec.kw,
+                print_func=self._print_param,
+                last=True,
+            )
+
+    def _print_param(self, param: p.Function.Parameter) -> None:
+        self._write_line("Parameter")
+        with self._child_level():
+            self._write_line(f"name: {param.name}")
+            self._write_optional_child("type", param.type, last=True)
+
+    def visit_type_assign(self, stmt: p.TypeAssign) -> None:
+        self._write_line("TypeAssign")
+        with self._child_level():
+            self._write_line(f"name: {stmt.name}")
+            self._write_line("type", last=True)
+            with self._child_level(single=True):
+                stmt.type.accept(self)
+
+    def visit_assign_stmt(self, stmt: p.AssignStmt) -> None:
+        self._write_line("AssignStmt")
+        with self._child_level():
+            self._write_sequence("targets", stmt.targets)
+            self._write_line("value", last=True)
+            with self._child_level(single=True):
+                stmt.value.accept(self)
+
+    def visit_return_stmt(self, stmt: p.ReturnStmt) -> None:
+        self._write_line("ReturnStmt")
+        with self._child_level():
+            self._write_optional_child("value", stmt.value, last=True)
+
+    def visit_if_stmt(self, stmt: p.IfStmt) -> None:
+        self._write_line("IfStmt")
+        with self._child_level():
+            self._write_line("test")
+            with self._child_level(single=True):
+                stmt.test.accept(self)
+            self._write_sequence("body", stmt.body)
+            self._write_sequence("orelse", stmt.orelse, last=True)
+
+    def visit_pass(self, stmt: p.Pass) -> None:
+        self._write_line("Pass")
+
+    def visit_for_stmt(self, stmt: p.ForStmt) -> None:
+        self._write_line("ForStmt")
+        with self._child_level():
+            self._write_line("target")
+            with self._child_level(single=True):
+                stmt.target.accept(self)
+            self._write_line("iterator")
+            with self._child_level(single=True):
+                stmt.iterator.accept(self)
+            self._write_sequence("body", stmt.body, last=True)
+
+    def visit_raw_stmt(self, stmt: p.RawStmt) -> None:
+        self._write_line("RawStmt")
+        with self._child_level(single=True):
+            self._write_line(f"stmt: {ast.unparse(stmt.stmt)}")
+
+    # Expressions
+
+    def visit_binary_expr(self, expr: p.BinaryExpr) -> None:
+        self._write_line("BinaryExpr")
+        with self._child_level():
+            self._write_line("left")
+            with self._child_level(single=True):
+                expr.left.accept(self)
+
+            self._write_line(f"operator: {expr.operator.__class__.__name__}")
+
+            self._write_line("right", last=True)
+            with self._child_level(single=True):
+                expr.right.accept(self)
+
+    def visit_compare_expr(self, expr: p.CompareExpr) -> None:
+        self._write_line("CompareExpr")
+        with self._child_level():
+            self._write_line("left")
+            with self._child_level(single=True):
+                expr.left.accept(self)
+
+            self._write_line(f"operator: {expr.operator.__class__.__name__}")
+
+            self._write_line("right", last=True)
+            with self._child_level(single=True):
+                expr.right.accept(self)
+
+    def visit_unary_expr(self, expr: p.UnaryExpr) -> None:
+        self._write_line("UnaryExpr")
+        with self._child_level():
+            self._write_line(f"operator: {expr.operator.__class__.__name__}")
+
+            self._write_line("right", last=True)
+            with self._child_level(single=True):
+                expr.right.accept(self)
+
+    def visit_call_expr(self, expr: p.CallExpr) -> None:
+        self._write_line("CallExpr")
+        with self._child_level():
+            self._write_line("callee")
+            with self._child_level(single=True):
+                expr.callee.accept(self)
+
+            self._write_sequence("arguments", expr.arguments)
+            self._write_line("keywords", last=True)
+            with self._child_level():
+                for i, (name, arg) in enumerate(expr.keywords.items()):
+                    self._idx = i
+                    if i == len(expr.keywords) - 1:
+                        self._mark_last()
+                    self._write_line(name)
+                    with self._child_level(single=True):
+                        arg.accept(self)
+
+    def visit_get_expr(self, expr: p.GetExpr) -> None:
+        self._write_line("GetExpr")
+        with self._child_level():
+            self._write_line("object")
+            with self._child_level(single=True):
+                expr.object.accept(self)
+            self._write_line(f"name: {expr.name}", last=True)
+
+    def visit_literal_expr(self, expr: p.LiteralExpr) -> None:
+        self._write_line("LiteralExpr")
+        with self._child_level(single=True):
+            self._write_line(f"value: {expr.value!r}")
+
+    def visit_variable_expr(self, expr: p.VariableExpr) -> None:
+        self._write_line("VariableExpr")
+        with self._child_level(single=True):
+            self._write_line(f"name: {expr.name}")
+
+    def visit_logical_expr(self, expr: p.LogicalExpr) -> None:
+        self._write_line("LogicalExpr")
+        with self._child_level():
+            self._write_line("left")
+            with self._child_level(single=True):
+                expr.left.accept(self)
+
+            self._write_line(f"operator: {expr.operator.__class__.__name__}")
+
+            self._write_line("right", last=True)
+            with self._child_level(single=True):
+                expr.right.accept(self)
+
+    def visit_cast_expr(self, expr: p.CastExpr) -> None:
+        self._write_line("CastExpr")
+        with self._child_level():
+            self._write_line("type")
+            with self._child_level(single=True):
+                expr.type.accept(self)
+            self._write_line("expr")
+            with self._child_level(single=True):
+                expr.expr.accept(self)
+            self._write_line(f"unsafe: {expr.unsafe}", last=True)
+
+    def visit_ternary_expr(self, expr: p.TernaryExpr) -> None:
+        self._write_line("TernaryExpr")
+        with self._child_level():
+            self._write_line("test")
+            with self._child_level(single=True):
+                expr.test.accept(self)
+
+            self._write_line("if_true")
+            with self._child_level(single=True):
+                expr.if_true.accept(self)
+
+            self._write_line("if_false", last=True)
+            with self._child_level(single=True):
+                expr.if_false.accept(self)
+
+    def visit_list_expr(self, expr: p.ListExpr) -> None:
+        self._write_line("ListExpr")
+        with self._child_level():
+            self._write_sequence("items", expr.items, last=True)
+
+    def visit_dict_expr(self, expr: p.DictExpr) -> None:
+        self._write_line("DictExpr")
+        with self._child_level():
+            self._write_sequence(
+                "keys",
+                expr.keys,
+                print_func=lambda k: (
+                    self._write_line("None") if k is None else k.accept(self)
+                ),
+            )
+            self._write_sequence("values", expr.values, last=True)
+
+    def visit_subscript_expr(self, expr: p.SubscriptExpr) -> None:
+        self._write_line("SubscriptExpr")
+        with self._child_level():
+            self._write_line("object")
+            with self._child_level(single=True):
+                expr.object.accept(self)
+            self._write_line("index", last=True)
+            with self._child_level(single=True):
+                expr.index.accept(self)
+
+    def visit_slice_expr(self, expr: p.SliceExpr) -> None:
+        self._write_line("SliceExpr")
+        with self._child_level():
+            self._write_optional_child("lower", expr.lower)
+            self._write_optional_child("upper", expr.upper)
+            self._write_optional_child("step", expr.step, last=True)
+
+    def visit_tuple_expr(self, expr: p.TupleExpr) -> None:
+        self._write_line("TupleExpr")
+        with self._child_level():
+            self._write_sequence("items", expr.items, last=True)
+
+    def visit_raw_expr(self, expr: p.RawExpr) -> None:
+        self._write_line("RawExpr")
+        with self._child_level(single=True):
+            self._write_line(f"expr: {ast.unparse(expr.expr)}")

midas/ast/python.py

@@ -14,6 +14,27 @@ from midas.ast.location import Location
 
 T = TypeVar("T")
 
+@dataclass(frozen=True, kw_only=True)
+class ParamSpec:
+    pos: list[Function.Parameter]
+    mixed: list[Function.Parameter]
+    kw: list[Function.Parameter]
+
+    @property
+    def all(self) -> list[Function.Parameter]:
+        return self.pos + self.mixed + self.kw
+
+
+@dataclass(frozen=True, kw_only=True)
+class ImportAlias:
+    location: Location
+    name: str
+    alias: Optional[str] = None
+
+    @property
+    def imported_name(self) -> str:
+        return self.alias if self.alias is not None else self.name
+
 
 ####################
 # Type annotations #
@@ -44,7 +65,7 @@ class MidasType(ABC):
 @dataclass(frozen=True)
 class BaseType(MidasType):
     base: str
-    param: Optional[MidasType]
+    args: tuple[MidasType, ...]
 
     def accept(self, visitor: MidasType.Visitor[T]) -> T:
         return visitor.visit_base_type(self)
@@ -113,6 +134,12 @@ class Stmt(ABC):
         @abstractmethod
         def visit_for_stmt(self, stmt: ForStmt) -> T: ...
 
+        @abstractmethod
+        def visit_import_stmt(self, stmt: ImportStmt) -> T: ...
+
+        @abstractmethod
+        def visit_from_import_stmt(self, stmt: FromImportStmt) -> T: ...
+
         @abstractmethod
         def visit_raw_stmt(self, stmt: RawStmt) -> T: ...
 
@@ -128,25 +155,17 @@ class ExpressionStmt(Stmt):
 @dataclass(frozen=True)
 class Function(Stmt):
     name: str
-    posonlyargs: list[Argument]
-    args: list[Argument]
-    sink: Optional[Argument]
-    kwonlyargs: list[Argument]
-    kw_sink: Optional[Argument]
+    params: ParamSpec
     returns: Optional[MidasType]
     body: list[Stmt]
 
     @dataclass(frozen=True, kw_only=True)
-    class Argument:
+    class Parameter:
         location: Optional[Location] = None
         name: str
         type: Optional[MidasType]
         default: Optional[Expr]
 
-    @property
-    def all_args(self) -> list[Argument]:
-        return self.posonlyargs + self.args + self.kwonlyargs
-
     def accept(self, visitor: Stmt.Visitor[T]) -> T:
         return visitor.visit_function(self)
 
@@ -205,6 +224,24 @@ class ForStmt(Stmt):
         return visitor.visit_for_stmt(self)
 
 
+@dataclass(frozen=True)
+class ImportStmt(Stmt):
+    imports: list[ImportAlias]
+
+    def accept(self, visitor: Stmt.Visitor[T]) -> T:
+        return visitor.visit_import_stmt(self)
+
+
+@dataclass(frozen=True)
+class FromImportStmt(Stmt):
+    module: Optional[str]
+    imports: list[ImportAlias]
+    level: int
+
+    def accept(self, visitor: Stmt.Visitor[T]) -> T:
+        return visitor.visit_from_import_stmt(self)
+
+
 @dataclass(frozen=True)
 class RawStmt(Stmt):
     stmt: ast.stmt
@@ -268,6 +305,9 @@ class Expr(ABC):
         @abstractmethod
         def visit_slice_expr(self, expr: SliceExpr) -> T: ...
 
+        @abstractmethod
+        def visit_tuple_expr(self, expr: TupleExpr) -> T: ...
+
         @abstractmethod
         def visit_raw_expr(self, expr: RawExpr) -> T: ...
 
@@ -402,6 +442,14 @@ class SliceExpr(Expr):
         return visitor.visit_slice_expr(self)
 
 
+@dataclass(frozen=True)
+class TupleExpr(Expr):
+    items: tuple[Expr, ...]
+
+    def accept(self, visitor: Expr.Visitor[T]) -> T:
+        return visitor.visit_tuple_expr(self)
+
+
 @dataclass(frozen=True)
 class RawExpr(Expr):
     expr: ast.expr

midas/checker/builtins.midas

@@ -178,4 +178,100 @@ extend dict[K, V] {
     // def __ior__: fn(value: SupportsKeysAndGetItem[K, V], /) -> dict[K, V]
     // def __ior__: fn(value: Iterable[tuple[K, V]], /) -> dict[K, V]
 
-}
+}
+
+extend str {
+    def capitalize: fn() -> str
+    def casefold: fn() -> str
+    def center: fn(width: int, fillchar: str?, /) -> str
+    def count: fn(sub: str, start: None?, end: None?, /) -> int
+    def count: fn(sub: str, start: int, end: None?, /) -> int
+    def count: fn(sub: str, start: None, end: int, /) -> int
+    def count: fn(sub: str, start: int, end: int, /) -> int
+    def encode: fn(encoding: str?, errors: str?) -> bytes
+    def endswith: fn(suffix: str, start: None?, end: None?, /) -> bool
+    def endswith: fn(suffix: str, start: int, end: None?, /) -> bool
+    def endswith: fn(suffix: str, start: None, end: int, /) -> bool
+    def endswith: fn(suffix: str, start: int, end: int, /) -> bool
+    def expandtabs: fn(tabsize: int?) -> str
+    def find: fn(sub: str, start: None?, end: None?, /) -> int
+    def find: fn(sub: str, start: int, end: None?, /) -> int
+    def find: fn(sub: str, start: None, end: int, /) -> int
+    def find: fn(sub: str, start: int, end: int, /) -> int
+    // def format: fn(*args: object, **kwargs: object) -> str
+    // def format_map: fn(mapping: _FormatMapMapping, /) -> str
+    def index: fn(sub: str, start: None?, end: None?, /) -> int
+    def index: fn(sub: str, start: int, end: None?, /) -> int
+    def index: fn(sub: str, start: None, end: int, /) -> int
+    def index: fn(sub: str, start: int, end: int, /) -> int
+    def isalnum: fn() -> bool
+    def isalpha: fn() -> bool
+    def isascii: fn() -> bool
+    def isdecimal: fn() -> bool
+    def isdigit: fn() -> bool
+    def isidentifier: fn() -> bool
+    def islower: fn() -> bool
+    def isnumeric: fn() -> bool
+    def isprintable: fn() -> bool
+    def isspace: fn() -> bool
+    def istitle: fn() -> bool
+    def isupper: fn() -> bool
+    def join: fn(iterable: list[str], /) -> str  // TODO: use Iterable
+    def ljust: fn(width: int, fillchar: str?, /) -> str
+    def lower: fn() -> str
+    def lstrip: fn(chars: None?, /) -> str
+    def lstrip: fn(chars: str, /) -> str
+    def partition: fn(sep: str, /) -> tuple[str, str, str]
+    
+    def replace: fn(old: str, new: str, count: int?, /) -> str
+
+    def removeprefix: fn(prefix: str, /) -> str
+    def removesuffix: fn(suffix: str, /) -> str
+    def rfind: fn(sub: str, start: None?, end: None?, /) -> int
+    def rfind: fn(sub: str, start: int, end: None?, /) -> int
+    def rfind: fn(sub: str, start: None, end: int, /) -> int
+    def rfind: fn(sub: str, start: int, end: int, /) -> int
+    def rindex: fn(sub: str, start: None?, end: None?, /) -> int
+    def rindex: fn(sub: str, start: int, end: None?, /) -> int
+    def rindex: fn(sub: str, start: None, end: int, /) -> int
+    def rindex: fn(sub: str, start: int, end: int, /) -> int
+    def rjust: fn(width: int, fillchar: str?, /) -> str
+    def rpartition: fn(sep: str, /) -> tuple[str, str, str]
+    def rsplit: fn(sep: None?, maxsplit: int?) -> list[str]
+    def rsplit: fn(sep: str, maxsplit: int?) -> list[str]
+    def rstrip: fn(chars: None?, /) -> str
+    def rstrip: fn(chars: str, /) -> str
+    def split: fn(sep: None?, maxsplit: int?) -> list[str]
+    def split: fn(sep: str, maxsplit: int?) -> list[str]
+    def splitlines: fn(keepends: bool?) -> list[str]
+    def startswith: fn(prefix: str, start: None?, end: None?, /) -> bool
+    def startswith: fn(prefix: str, start: int, end: None?, /) -> bool
+    def startswith: fn(prefix: str, start: None, end: int, /) -> bool
+    def startswith: fn(prefix: str, start: int, end: int, /) -> bool
+    def strip: fn(chars: None?, /) -> str
+    def strip: fn(chars: str, /) -> str
+    def swapcase: fn() -> str
+    def title: fn() -> str
+    // def translate: fn(table: _TranslateTable, /) -> str
+    def upper: fn() -> str
+    def zfill: fn(width: int, /) -> str
+    def __add__: fn(value: str, /) -> str
+    // Incompatible with Sequence.__contains__
+    def __contains__: fn(key: str, /) -> bool
+    def __eq__: fn(value: object, /) -> bool
+    def __ge__: fn(value: str, /) -> bool
+    def __getitem__: fn(key: slice, /) -> str
+    def __getitem__: fn(key: int, /) -> str
+    def __gt__: fn(value: str, /) -> bool
+    def __hash__: fn() -> int
+    // def __iter__: fn() -> Iterator[str]
+    def __le__: fn(value: str, /) -> bool
+    def __len__: fn() -> int
+    def __lt__: fn(value: str, /) -> bool
+    def __mod__: fn(value: Any, /) -> str
+    def __mul__: fn(value: int, /) -> str
+    def __ne__: fn(value: object, /) -> bool
+    def __rmul__: fn(value: int, /) -> str
+    def __getnewargs__: fn() -> tuple[str]
+    def __format__: fn(format_spec: str, /) -> str
+}

midas/checker/builtins.py

@@ -15,10 +15,14 @@ if TYPE_CHECKING:
 
 
 BUILTIN_SUBTYPES: dict[str, set[str]] = {
-    "object": {"float", "list", "dict", "str"},
+    "object": {"float", "list", "dict", "str", "bytes", "tuple"},
     "float": {"int"},
-    "int": {"bool"},
 }
+"""
+Hard-coded subtype relationships between builtin types
+
+Circular dependencies and diamond inheritance MUST be avoided
+"""
 
 
 def define_builtins(reg: TypesRegistry):
@@ -26,12 +30,15 @@ def define_builtins(reg: TypesRegistry):
     any = reg.define_type("Any", TopType())
     unit = reg.define_type("None", UnitType())
     object = reg.define_type("object", BaseType(name="object"))
+    bytes = reg.define_type("bytes", BaseType(name="bytes"))
     bool = reg.define_type("bool", BaseType(name="bool"))
     int = reg.define_type("int", BaseType(name="int"))
     float = reg.define_type("float", BaseType(name="float"))
     str = reg.define_type("str", BaseType(name="str"))
     slice = reg.define_type("slice", BaseType(name="slice"))
 
+    tuple = reg.define_type("tuple", BaseType(name="tuple"))
+
     list = reg.define_type(
         "list",
         GenericType(

midas/checker/checker.py

@@ -10,6 +10,11 @@ from midas.utils import TypedAST
 
 
 class TypeChecker:
+    """Type checking dispatcher
+
+    Contains a typer for Midas and one for Python, as well as the types registry
+    """
+
     def __init__(self):
         self.types: TypesRegistry = TypesRegistry()
         self.reporter: Reporter = Reporter()

midas/checker/diagnostic.py

@@ -14,6 +14,12 @@ class DiagnosticType(StrEnum):
 
 @dataclass(frozen=True)
 class Diagnostic:
+    """Information about a diagnostic (warning, errors, etc.)
+
+    Holds a location, a diagnostic type and a message.
+    Optionally bound to a file path
+    """
+
     file_path: Optional[str]
     location: Location
     type: DiagnosticType
@@ -21,6 +27,18 @@ class Diagnostic:
 
     @property
     def location_str(self) -> str:
+        """Get diagnostic type and location as a human readable string
+
+        The location is formatted as "<Type> in <file> from L<start_line>:<start_col> to <end_line>:<end_col>",
+        for example: "Error in /home/user/Desktop/script.py from L12:5 to L12:8"
+
+        If the file is `None`, the "in ..." section is excluded from the result.<br>
+        If the location's end is not specified, the formulation "at L<start_line>:<start_col>" is used.
+
+        Returns:
+            str: the formatted type and location string
+        """
+
         start_loc: str = f"L{self.location.lineno}:{self.location.col_offset+1}"
         end_loc: Optional[str] = ""
         if (

midas/checker/dispatcher.py

@@ -0,0 +1,532 @@
+import logging
+from dataclasses import dataclass
+from enum import StrEnum
+from typing import Generic, Optional, Protocol, TypeVar, Union
+
+from midas.ast.location import Location
+from midas.checker.registry import TypesRegistry
+from midas.checker.reporter import FileReporter
+from midas.checker.types import (
+    AppliedType,
+    DerivedType,
+    Function,
+    GenericType,
+    OverloadedFunction,
+    Type,
+    UnknownType,
+)
+from midas.checker.unifier import Unifier
+
+
+class HasLocation(Protocol):
+    @property
+    def location(self) -> Location: ...
+
+
+E = TypeVar("E", bound=HasLocation)
+
+TypedExpr = tuple[E, Type]
+"""An expression and its type"""
+
+
+@dataclass(frozen=True, kw_only=True)
+class MappedArgument(Generic[E]):
+    """An argument passed in a call and the corresponding parameter"""
+
+    arg_expr: E
+    arg_type: Type
+    parameter: Function.Parameter
+
+
+@dataclass(frozen=True, kw_only=True)
+class OverloadCandidate:
+    """An overloaded function call candidate with its mapped arguments"""
+
+    function: Function
+    mapped: list[MappedArgument]
+
+
+class CallError(StrEnum):
+    """Reason of a call error"""
+
+    INVALID_ARGS = "Invalid arguments"
+    NO_MATCHING_OVERLOAD = "No matching overload"
+    IMPOSSIBLE_UNIFICATION = "Parameters unification failed"
+    NOT_CALLABLE = "Not callable"
+
+
+@dataclass(frozen=True, kw_only=True)
+class CallResult:
+    """The result of a function call
+
+    Holds a return type, an optional error reason and message
+    """
+
+    error: Optional[CallError] = None
+    """The reason of the error, if there is one"""
+
+    result: Type = UnknownType()
+    """The result type. `UnknownType()` if the call is invalid"""
+
+    message: Optional[str] = None
+    """An optional error message"""
+
+    @property
+    def is_valid(self) -> bool:
+        """Whether the call is valid (i.e. no error)"""
+        return self.error is None
+
+    @property
+    def error_message(self) -> str:
+        """A descriptive message for the error, if there is one"""
+        if self.message is not None:
+            return self.message
+        if self.error is not None:
+            return str(self.error)
+        return ""
+
+
+class CallDispatcher(Generic[E]):
+    """Helper class to handle dispatching calls and mapping arguments
+
+    This class is responsible for mapping call-site arguments to function
+    parameters, verifying the validity of calls and computing their
+    return types
+
+    :class:`CallDispatcher` is generic to handle AST nodes from both Midas and Python
+    """
+
+    def __init__(self, types: TypesRegistry, reporter: FileReporter) -> None:
+        self.types: TypesRegistry = types
+        self.reporter: FileReporter = reporter
+        self.logger: logging.Logger = logging.getLogger("CallDispatcher")
+
+    def set_reporter(self, reporter: FileReporter):
+        self.reporter = reporter
+
+    def get_result(
+        self,
+        location: Location,
+        callee: Type,
+        positional: list[TypedExpr[E]],
+        keywords: dict[str, TypedExpr[E]],
+        report_errors: bool = True,
+    ) -> CallResult:
+        """Get the result type of a function call
+
+        If the callee has overloads, this function will try to resolve the
+        appropriate signature.
+        Argument types are matched with the defined parameters.
+        This function doesn't take the raw expression as a parameter to
+        accommodate for desugared calls such as for operators.
+
+        Args:
+            location (Location): the call location
+            callee (Type): the called function
+            positional (list[TypedExpr]): the list of positional arguments
+            keywords (dict[str, TypedExpr]): the map of keyword arguments
+            report_errors (bool, optional): whether type errors should be reported as diagnostics. Defaults to True.
+
+        Returns:
+            CallResult: the call result, either a type or an error
+        """
+        match callee:
+            case Function() as function:
+                valid: bool
+                mapped: list[MappedArgument[E]]
+                valid, mapped = self.map_call_arguments(
+                    function, location, positional, keywords
+                )
+                valid = valid and self._are_arguments_valid(mapped, report_errors)
+                if not valid:
+                    return CallResult(error=CallError.INVALID_ARGS)
+                return CallResult(result=function.returns)
+
+            case OverloadedFunction(overloads=overloads):
+                res = self._match_overload(
+                    overloads, location, positional, keywords, report_errors
+                )
+                if res[0] is None:
+                    return CallResult(
+                        error=CallError.NO_MATCHING_OVERLOAD,
+                        message=res[1],
+                    )
+                return CallResult(result=res[0].returns)
+
+            case AppliedType(body=body):
+                return self.get_result(
+                    location, body, positional, keywords, report_errors
+                )
+
+            case UnknownType():
+                return CallResult(result=UnknownType())
+
+            case DerivedType(type=base):
+                return self.get_result(
+                    location, base, positional, keywords, report_errors
+                )
+
+            case GenericType():
+                unifier: Unifier = Unifier(self.types)
+                pos: list[Type] = [a[1] for a in positional]
+                kw: dict[str, Type] = {k: v[1] for k, v in keywords.items()}
+                unified: Optional[Type] = unifier.unify_call(callee, pos, kw)
+                if unified is None:
+                    pos_str: str = ", ".join(str(t) for t in pos)
+                    kw_str: str = ", ".join(f"{k}: {v}" for k, v in kw.items())
+                    message: str = (
+                        f"Could not unify {callee}={callee.body} with pos=[{pos_str}] and kw={{{kw_str}}}"
+                    )
+                    if report_errors:
+                        self.reporter.error(location, message)
+                    return CallResult(
+                        error=CallError.IMPOSSIBLE_UNIFICATION,
+                        message=message,
+                    )
+                return self.get_result(
+                    location,
+                    unified,
+                    positional,
+                    keywords,
+                    report_errors,
+                )
+
+            case _:
+                message: str = f"{callee} ({callee.__class__.__name__}) is not callable"
+                if report_errors:
+                    self.reporter.error(location, message)
+                return CallResult(
+                    error=CallError.NOT_CALLABLE,
+                    message=message,
+                )
+
+    def _unwrap_function(
+        self,
+        callee: Type,
+        positional: list[TypedExpr[E]],
+        keywords: dict[str, TypedExpr[E]],
+    ) -> Union[tuple[Function, None], tuple[None, CallError]]:
+        """Unwrap a type to get a callable `Function`
+
+        Args:
+            callee (Type): the called type
+            positional (list[TypedExpr[E]]): the list of positional arguments
+            keywords (dict[str, TypedExpr[E]]): the map of keyword arguments
+
+        Returns:
+            Union[tuple[Function, None], tuple[None, CallError]]: a tuple
+                containing the callable `Function` type, or `None` if it could
+                not be unwrapped, and an error, or `None` if there was none.
+        """
+        match callee:
+            case DerivedType(type=base):
+                return self._unwrap_function(base, positional, keywords)
+
+            case GenericType():
+                unifier: Unifier = Unifier(self.types)
+                unified: Optional[Type] = unifier.unify_call(
+                    callee,
+                    [a[1] for a in positional],
+                    {k: v[1] for k, v in keywords.items()},
+                )
+                if unified is None:
+                    return None, CallError.IMPOSSIBLE_UNIFICATION
+                return self._unwrap_function(unified, positional, keywords)
+
+            case Function():
+                return callee, None
+
+            case AppliedType(body=body):
+                return self._unwrap_function(body, positional, keywords)
+
+            case _:
+                return None, CallError.NOT_CALLABLE
+
+    def _are_arguments_valid(
+        self,
+        arguments: list[MappedArgument[E]],
+        report_errors: bool = True,
+    ) -> bool:
+        """Check whether the passed argument types correspond to their matched parameter definitions
+
+        Args:
+            arguments (list[MappedArgument]): the list of argument/parameter pairs
+            report_errors (bool, optional): whether type errors should be reported as diagnostics. Defaults to True.
+
+        Returns:
+            bool: True if all arguments fit the matching parameter definitions, False otherwise
+        """
+        valid: bool = True
+        for arg in arguments:
+            if arg.parameter.unsupported:
+                # Always report error
+                self.reporter.error(
+                    arg.arg_expr.location, f"Unsupported argument {arg.parameter.name}"
+                )
+
+            if not self.types.is_subtype(arg.arg_type, arg.parameter.type):
+                if report_errors:
+                    self.reporter.error(
+                        arg.arg_expr.location,
+                        f"Wrong type for argument '{arg.parameter.name}', expected {arg.parameter.type}, got {arg.arg_type}",
+                    )
+                valid = False
+        return valid
+
+    def _match_overload(
+        self,
+        overloads: list[Type],
+        location: Location,
+        positional: list[TypedExpr[E]],
+        keywords: dict[str, TypedExpr[E]],
+        report_errors: bool = True,
+    ) -> Union[tuple[Function, None], tuple[None, str]]:
+        """Try and resolve the appropriate overload for the given arguments
+
+        Args:
+            overloads (list[Type]): the list of possible overloads
+            location (Location): the call location
+            positional (list[TypedExpr]): the list of positional arguments
+            keywords (dict[str, TypedExpr]): the map of keywords arguments
+            report_errors (bool, optional): whether type errors should be reported as diagnostics. Defaults to True.
+
+        Returns:
+            Union[tuple[Function, None], tuple[None, str]]: a tuple containing
+                the resolved function signature if it can be determined
+                unambiguously, or `None`, and an error message, or `None`
+        """
+        candidates: list[OverloadCandidate] = []
+        errors: list[CallError] = []
+        for overload in overloads:
+            function, unwrap_error = self._unwrap_function(
+                overload, positional, keywords
+            )
+            if function is None:
+                errors.append(unwrap_error)  # type: ignore
+                continue
+
+            valid, mapped = self.map_call_arguments(
+                function=function,
+                location=location,
+                positional=positional,
+                keywords=keywords,
+                report_errors=False,
+            )
+            if valid and self._are_arguments_valid(mapped, report_errors=False):
+                candidates.append(
+                    OverloadCandidate(
+                        function=function,
+                        mapped=mapped,
+                    )
+                )
+
+        pos_types: str = ", ".join(str(type) for _, type in positional)
+        kw_types: str = ", ".join(
+            f"{name}: {type}" for name, (_, type) in keywords.items()
+        )
+        for_args: str = f"for arguments pos=[{pos_types}] and kw={{{kw_types}}}"
+
+        n_candidates: int = len(candidates)
+
+        # Exactly 1 match -> return it
+        if n_candidates == 1:
+            return candidates[0].function, None
+
+        # No match -> invalid call
+        if n_candidates == 0:
+            overloads_str: str = ", ".join(map(str, overloads))
+            errors_str: str = ", ".join(errors)
+            message: str = (
+                f"No matching overload in [{overloads_str}] {for_args} (errors: {errors_str})"
+            )
+            if report_errors:
+                self.reporter.error(location, message)
+            return None, message
+
+        # Multiple matches -> see if one <: all others (more specific)
+        for i1, c1 in enumerate(candidates):
+            mapped1: list[MappedArgument[E]] = c1.mapped
+            best_match: bool = True
+            for i2, c2 in enumerate(candidates):
+                if i1 == i2:
+                    continue
+                mapped2: list[MappedArgument[E]] = c2.mapped
+                if not self._are_mapped_subtypes(mapped1, mapped2):
+                    best_match = False
+                    break
+                self.logger.debug(f"{c1.function} is a full overload of {c2.function}")
+            if best_match:
+                return c1.function, None
+
+        candidates_str: str = ", ".join(
+            str(candidate.function) for candidate in candidates
+        )
+        message: str = f"Multiple matching overloads {for_args}: {candidates_str}"
+        if report_errors:
+            self.reporter.error(location, message)
+        return None, message
+
+    def map_call_arguments(
+        self,
+        function: Function,
+        location: Location,
+        positional: list[TypedExpr[E]],
+        keywords: dict[str, TypedExpr[E]],
+        report_errors: bool = True,
+    ) -> tuple[bool, list[MappedArgument]]:
+        """Map call arguments to a function's parameters as defined in its signature
+
+        This method maps positional-only, keyword-only and mixed parameter definitions
+        with the arguments passed at the call site
+
+        Any mismatched, missing or unexpected argument is reported as a diagnostic,
+        unless `report_errors` is set to `False`
+
+        Args:
+            function (Function): the function definition
+            location (Location): the call location
+            positional (list[TypedExpr]): the list of positional arguments
+            keywords (dict[str, TypedExpr]): the map of keyword arguments
+            report_errors (bool, optional): whether type errors should be reported as diagnostics. Defaults to True.
+
+        Returns:
+            tuple[bool, list[MappedArgument]]: a boolean reporting whether
+                the call is valid and the list of mapped arguments
+        """
+        set_params: set[str] = set()
+
+        required_positional: list[str] = [
+            param.name
+            for param in function.params.pos + function.params.mixed
+            if param.required
+        ]
+        required_keyword: list[str] = [
+            param.name for param in function.params.kw if param.required
+        ]
+
+        mapped: list[MappedArgument[E]] = []
+
+        pos_params: list[Function.Parameter] = list(function.params.pos)
+        mixed_params: list[Function.Parameter] = list(function.params.mixed)
+        kw_params: dict[str, Function.Parameter] = {
+            param.name: param for param in function.params.kw
+        }
+
+        valid_call: bool = True
+
+        # TODO: handle *args and **kwargs sinks
+        for arg in positional:
+            param: Function.Parameter
+            if len(pos_params) != 0:
+                param = pos_params.pop(0)
+            elif len(mixed_params) != 0:
+                param = mixed_params.pop(0)
+            else:
+                if report_errors:
+                    self.reporter.error(
+                        arg[0].location, "Too many positional arguments"
+                    )
+                valid_call = False
+                break
+            name: str = param.name
+            if name in required_positional:
+                required_positional.remove(name)
+            if name in required_keyword:
+                required_keyword.remove(name)
+            set_params.add(name)
+            mapped.append(
+                MappedArgument(
+                    arg_expr=arg[0],
+                    arg_type=arg[1],
+                    parameter=param,
+                )
+            )
+
+        kw_params.update({param.name: param for param in mixed_params})
+        for name, arg in keywords.items():
+            param: Function.Parameter
+            if name not in kw_params:
+                if report_errors:
+                    if name in set_params:
+                        self.reporter.error(
+                            arg[0].location, f"Multiple values for parameter '{name}'"
+                        )
+                    else:
+                        self.reporter.error(
+                            arg[0].location, f"Unknown keyword parameter '{name}'"
+                        )
+                valid_call = False
+                continue
+            param = kw_params.pop(name)
+            if name in required_positional:
+                required_positional.remove(name)
+            if name in required_keyword:
+                required_keyword.remove(name)
+            set_params.add(name)
+            mapped.append(
+                MappedArgument(
+                    arg_expr=arg[0],
+                    arg_type=arg[1],
+                    parameter=param,
+                )
+            )
+
+        def join_params(params: list[str]) -> str:
+            params = list(map(lambda p: f"'{p}'", params))
+            if len(params) == 0:
+                return ""
+            if len(params) == 1:
+                return params[0]
+            return ", ".join(params[:-1]) + " and " + params[-1]
+
+        if len(required_positional) != 0:
+            plural: str = "" if len(required_positional) == 1 else "s"
+            params: str = join_params(required_positional)
+            if report_errors:
+                self.reporter.error(
+                    location,
+                    f"Missing required positional argument{plural}: {params}",
+                )
+            valid_call = False
+
+        if len(required_keyword) != 0:
+            plural: str = "" if len(required_keyword) == 1 else "s"
+            params: str = join_params(required_keyword)
+            if report_errors:
+                self.reporter.error(
+                    location,
+                    f"Missing required keyword argument{plural}: {params}",
+                )
+            valid_call = False
+
+        return valid_call, mapped
+
+    def _are_mapped_subtypes(
+        self, mapped1: list[MappedArgument[E]], mapped2: list[MappedArgument[E]]
+    ) -> bool:
+        """Check whether the given argument mappings are subtype/supertype of one another
+
+        This function checks whether the argument mappings `mapped1` are subtypes
+        of `mapped2`. If any of the parameter type in `mapped1` is not a subtype
+        of the corresponding parameter in `mapped2`, `False` is returned.
+
+        This is used to check whether a given overload is a more specific
+        function / a subtype of another.
+
+        Args:
+            mapped1 (list[MappedArgument]): the first argument mappings (subtype)
+            mapped2 (list[MappedArgument]): the second argument mappings (supertype)
+
+        Returns:
+            bool: `True` if `mapped1` is a subtype of `mapped2`, `False` otherwise
+        """
+        by_expr: dict[E, Type] = {}
+        for arg in mapped1:
+            by_expr[arg.arg_expr] = arg.parameter.type
+
+        for arg in mapped2:
+            type2: Type = arg.parameter.type
+            type1: Type = by_expr[arg.arg_expr]
+            if not self.types.is_subtype(type1, type2):
+                return False
+        return True

midas/checker/evaluator.py

@@ -2,6 +2,7 @@ from dataclasses import dataclass
 from typing import Any, Callable, Optional
 
 import midas.ast.midas as m
+from midas.ast.location import Location
 from midas.checker.preamble import Preamble
 from midas.checker.registry import TypesRegistry
 from midas.checker.reporter import FileReporter
@@ -11,10 +12,18 @@ from midas.lexer.token import TokenType
 
 @dataclass(frozen=True, kw_only=True)
 class PartialPredicate(Predicate):
+    """A partially applied predicate"""
+
     scope: dict[str, Any]
+    """A dictionary of already applied parameters"""
 
 
 class Evaluator(m.Expr.Visitor[Any]):
+    """Helper class to evaluate an expression
+
+    This class is used to evaluate constraint types on literals at compile-time.
+    """
+
     def __init__(self, types: TypesRegistry, reporter: Optional[FileReporter] = None):
         self.types: TypesRegistry = types
         self.reporter: Optional[FileReporter] = reporter
@@ -22,16 +31,51 @@ class Evaluator(m.Expr.Visitor[Any]):
         self.scopes: list[dict[str, Any]] = [{}]
 
     def evaluate(self, expr: m.Expr) -> Any:
+        """Evaluate the given expression
+
+        Args:
+            expr (m.Expr): the expression to evaluate
+
+        Returns:
+            Any: the value of the expression
+        """
         value: Any = expr.accept(self)
         if self.reporter is not None:
             self.reporter.debug(expr.location, f"Value: {value}")
         return value
 
     def get_value(self, name: str) -> Any:
+        """Get the value of a variable in the current scope
+
+        Args:
+            name (str): the name of the variable
+
+        Raises:
+            KeyError: if the variable is not defined
+
+        Returns:
+            Any: the value of the variable
+        """
         scope: dict[str, Any] = self.scopes[-1]
         return scope[name]
 
     def set_value(self, name: str, value: Any, force_declare: bool = False):
+        """Set the value of a variable
+
+        If `force_declare` is `False`, this function first tries to find the
+        closest scope in which the variable is defined and assign the value in
+        that scope, if it can find one.
+
+        If `force_declare` is `True` or if the variable is not defined in any
+        scope, it is declare and assigned in the current scope
+
+        Args:
+            name (str): the name of the variable
+            value (Any): the value of the variable
+            force_declare (bool, optional): if `False` and the variable is
+                defined in a scope, the value is assigned in that scope (the
+                closest if there are multiple declarations). Defaults to False.
+        """
         if not force_declare:
             for scope in reversed(self.scopes):
                 if name in scope:
@@ -56,6 +100,8 @@ class Evaluator(m.Expr.Visitor[Any]):
         left: Any = self.evaluate(expr.left)
         right: Any = self.evaluate(expr.right)
         match expr.operator.type:
+            case TokenType.PLUS:
+                return left + right
             case TokenType.MINUS:
                 return left - right
             case TokenType.STAR:
@@ -80,8 +126,12 @@ class Evaluator(m.Expr.Visitor[Any]):
     def visit_unary_expr(self, expr: m.UnaryExpr) -> Any:
         right: Any = self.evaluate(expr.right)
         match expr.operator.type:
+            case TokenType.PLUS:
+                return +right
             case TokenType.MINUS:
                 return -right
+            case TokenType.BANG:
+                return not right
             case _:
                 raise NotImplementedError
 
@@ -94,7 +144,7 @@ class Evaluator(m.Expr.Visitor[Any]):
 
         match callee:
             case Predicate():
-                return self._evaluate_predicate(callee, args, kwargs)
+                return self._evaluate_predicate(expr.location, callee, args, kwargs)
             case _ if callable(callee):
                 return callee(*args, **kwargs)
             case _:
@@ -131,8 +181,22 @@ class Evaluator(m.Expr.Visitor[Any]):
         return self.get_value("_")
 
     def _evaluate_predicate(
-        self, predicate: Predicate, args: list[Any], kwargs: dict[str, Any]
+        self,
+        location: Location,
+        predicate: Predicate,
+        args: list[Any],
+        kwargs: dict[str, Any],
     ) -> Any:
+        """Evaluate a predicate function call
+
+        Args:
+            predicate (Predicate): the predicate to evaluate
+            args (list[Any]): a list of positional arguments
+            kwargs (dict[str, Any]): a map of keyword arguments
+
+        Returns:
+            Any: the value returned by the predicate call
+        """
         res: Any = None
         if isinstance(predicate, PartialPredicate):
             self.scopes.append(predicate.scope)
@@ -140,7 +204,7 @@ class Evaluator(m.Expr.Visitor[Any]):
             self.scopes.append({})
         match predicate.type:
             case Function(returns=Function() as inner):
-                self._map_args(predicate.type, args, kwargs)
+                self._map_args(location, predicate.type, args, kwargs)
                 res = PartialPredicate(
                     type=inner,
                     body=predicate.body,
@@ -149,7 +213,7 @@ class Evaluator(m.Expr.Visitor[Any]):
                 )
 
             case Function():
-                self._map_args(predicate.type, args, kwargs)
+                self._map_args(location, predicate.type, args, kwargs)
                 res = self.evaluate(predicate.body)
 
             case _:
@@ -157,16 +221,45 @@ class Evaluator(m.Expr.Visitor[Any]):
         self.scopes.pop()
         return res
 
-    def _map_args(self, function: Function, args: list[Any], kwargs: dict[str, Any]):
-        positional: list[Function.Argument] = function.pos_args + function.args
-        keywords: dict[str, Function.Argument] = {
-            arg.name: arg for arg in function.args + function.kw_args
+    def _map_args(
+        self,
+        location: Location,
+        function: Function,
+        args: list[Any],
+        kwargs: dict[str, Any],
+    ):
+        """Map call arguments to a function's parameters and set their values in context
+
+        Each argument is mapped to a parameter of the function, then its value
+        is set in the context using :func:`set_value` with the parameter's name
+
+        Args:
+            function (Function): the called function
+            args (list[Any]): a list of positional arguments
+            kwargs (dict[str, Any]): a map of keyword arguments
+        """
+        positional: list[Function.Parameter] = (
+            function.params.pos + function.params.mixed
+        )
+        keywords: dict[str, Function.Parameter] = {
+            param.name: param for param in function.params.mixed + function.params.kw
         }
 
         for i, arg in enumerate(args):
-            param: Function.Argument = positional[i]
+            if i >= len(positional):
+                if self.reporter is not None:
+                    self.reporter.error(
+                        location,
+                        f"Too many positional arguments, expected at most {len(positional)}, got {len(args)}",
+                    )
+                break
+            param: Function.Parameter = positional[i]
             self.set_value(param.name, arg)
 
         for name, arg in kwargs.items():
-            param: Function.Argument = keywords[name]
+            if name not in keywords:
+                if self.reporter is not None:
+                    self.reporter.error(location, f"Unknown keyword argument '{name}'")
+                break
+            param: Function.Parameter = keywords[name]
             self.set_value(param.name, arg)

midas/checker/frames/column_groupby_methods.py

@@ -0,0 +1,240 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import TYPE_CHECKING
+
+import midas.ast.python as p
+from midas.ast.location import Location
+from midas.checker.dispatcher import CallResult
+from midas.checker.frames.utils import MethodRegistry, method
+from midas.checker.types import (
+    ColumnGroupBy,
+    ColumnType,
+    Function,
+    ParamSpec,
+    Type,
+    UnknownType,
+)
+
+if TYPE_CHECKING:
+    from midas.checker.python import TypedExpr
+
+
+@dataclass(frozen=True, kw_only=True)
+class Call:
+    """A column group-by method call, implements :class:`utils.MethodCall`"""
+
+    location: Location
+    call_expr: p.Expr
+    groupby: ColumnGroupBy
+    groupby_expr: p.Expr
+    positional: list[TypedExpr]
+    keywords: dict[str, TypedExpr]
+
+    @property
+    def subject(self) -> TypedExpr:
+        return (self.groupby_expr, self.groupby)
+
+
+class ColumnGroupByMethodRegistry(MethodRegistry[Call]):
+    """The method registry for column group-by types"""
+
+    NAMED_ARGS: dict[str, str] = {
+        "numeric_only": "bool",
+        "skipna": "bool",
+        "engine": "str",
+        "engine_kwargs": "dict",
+    }
+
+    def _aggregate(
+        self,
+        call: Call,
+        method: str,
+        params: list[str | tuple[str, str, bool]] = [],
+    ) -> Type:
+        """Compute the result type of an aggregate method call
+
+        Args:
+            call (Call): the call object
+            method (str): the method name to delegate on :class:`Column`
+            params (list[str | tuple[str, str, bool], optional): a list of extra
+                mixed parameters. The list can contain strings to include
+                parameters predefined in `NAMED_ARGS`, or tuples containing the
+                parameter's name, type and required flag. Defaults to [].
+
+        Returns:
+            Type: the result type
+        """
+        real_params: list[Function.Parameter] = []
+        for i, param in enumerate(params):
+            match param:
+                case str() as name:
+                    param = Function.Parameter(
+                        pos=i,
+                        name=name,
+                        type=self.types.get_type(self.NAMED_ARGS[name]),
+                        required=False,
+                    )
+                case (name, type, required):
+                    param = Function.Parameter(
+                        pos=i,
+                        name=name,
+                        type=self.types.get_type(type),
+                        required=required,
+                    )
+            real_params.append(param)
+
+        # TODO: maybe better to filter arguments and pass some, in case the
+        # return type depends on them
+        returns: Type = self.typer.call_method(
+            location=call.location,
+            call_expr=call.call_expr,
+            obj=(call.groupby_expr, call.groupby.column),
+            method_name=method,
+            positional=[],
+            keywords={},
+        )
+        if not isinstance(returns, ColumnType):
+            returns = ColumnType(type=UnknownType())
+        signature = Function(
+            params=ParamSpec(mixed=real_params),
+            returns=returns,
+        )
+
+        result: CallResult = self.dispatcher.get_result(
+            location=call.location,
+            callee=signature,
+            positional=call.positional,
+            keywords=call.keywords,
+        )
+        return result.result
+
+    @method()
+    def kurt(self, call: Call) -> Type:
+        return self._aggregate(
+            call,
+            "kurt",
+            ["skipna", "numeric_only"],
+        )
+
+    @method()
+    def max(self, call: Call) -> Type:
+        return self._aggregate(
+            call,
+            "max",
+            [
+                "numeric_only",
+                (
+                    "min_count",
+                    "int",
+                    False,
+                ),
+                "skipna",
+                "engine",
+                "engine_kwargs",
+            ],
+        )
+
+    @method()
+    def mean(self, call: Call) -> Type:
+        return self._aggregate(
+            call,
+            "mean",
+            ["numeric_only", "skipna", "engine", "engine_kwargs"],
+        )
+
+    @method()
+    def median(self, call: Call) -> Type:
+        return self._aggregate(
+            call,
+            "median",
+            ["numeric_only", "skipna"],
+        )
+
+    @method()
+    def min(self, call: Call) -> Type:
+        return self._aggregate(
+            call,
+            "min",
+            [
+                "numeric_only",
+                (
+                    "min_count",
+                    "int",
+                    False,
+                ),
+                "skipna",
+                "engine",
+                "engine_kwargs",
+            ],
+        )
+
+    @method()
+    def prod(self, call: Call) -> Type:
+        return self._aggregate(
+            call,
+            "prod",
+            [
+                "numeric_only",
+                (
+                    "min_count",
+                    "int",
+                    False,
+                ),
+                "skipna",
+            ],
+        )
+
+    @method()
+    def std(self, call: Call) -> Type:
+        return self._aggregate(
+            call,
+            "std",
+            [
+                (
+                    "ddof",
+                    "int",
+                    False,
+                ),
+                "engine",
+                "engine_kwargs",
+                "numeric_only",
+                "skipna",
+            ],
+        )
+
+    @method()
+    def sum(self, call: Call) -> Type:
+        return self._aggregate(
+            call,
+            "sum",
+            [
+                "numeric_only",
+                (
+                    "min_count",
+                    "int",
+                    False,
+                ),
+                "skipna",
+                "engine",
+                "engine_kwargs",
+            ],
+        )
+
+    @method()
+    def var(self, call: Call) -> Type:
+        return self._aggregate(
+            call,
+            "var",
+            [
+                (
+                    "var",
+                    "int",
+                    False,
+                ),
+                "engine",
+                "engine_kwargs",
+                "numeric_only",
+                "skipna",
+            ],
+        )

midas/checker/frames/column_manager.py

@@ -0,0 +1,182 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, Optional
+
+import midas.ast.python as p
+from midas.ast.location import Location
+from midas.checker.dispatcher import CallResult
+from midas.checker.frames.column_groupby_methods import Call as GroupByCall
+from midas.checker.frames.column_groupby_methods import ColumnGroupByMethodRegistry
+from midas.checker.frames.column_methods import Call, ColumnMethodRegistry
+from midas.checker.registry import TypesRegistry
+from midas.checker.reporter import FileReporter
+from midas.checker.types import (
+    ColumnGroupBy,
+    ColumnType,
+    Function,
+    OverloadedFunction,
+    ParamSpec,
+    Type,
+)
+
+if TYPE_CHECKING:
+    from midas.checker.python import PythonTyper, TypedExpr
+
+
+class ColumnManager:
+    """Helper class to handle methods and subscripts on column types"""
+
+    def __init__(self, typer: PythonTyper) -> None:
+        self.typer: PythonTyper = typer
+        self.method_resolver: ColumnMethodRegistry = ColumnMethodRegistry(self.typer)
+        self.groupby_method_resolver: ColumnGroupByMethodRegistry = (
+            ColumnGroupByMethodRegistry(self.typer)
+        )
+
+    def get(
+        self,
+        reporter: FileReporter,
+        location: Location,
+        column: ColumnType,
+        index: TypedExpr,
+    ) -> Type:
+        """Compute the type of a subscript access
+
+        Args:
+            reporter (FileReporter): the file reporter to use for diagnostics
+            location (Location): the subscript's location
+            column (DataFrameType): the column type
+            index (TypedExpr): the index
+
+        Returns:
+            Type: the resulting type
+        """
+
+        single = Function(
+            params=ParamSpec(
+                pos=[
+                    Function.Parameter(
+                        pos=0,
+                        name="index",
+                        type=self.typer.types.get_type("int"),
+                        required=True,
+                    )
+                ]
+            ),
+            returns=column.type,
+        )
+        slice = Function(
+            params=ParamSpec(
+                pos=[
+                    Function.Parameter(
+                        pos=0,
+                        name="slice",
+                        type=self.typer.types.get_type("slice"),
+                        required=True,
+                    )
+                ]
+            ),
+            returns=column,
+        )
+
+        overload = OverloadedFunction(overloads=[single, slice])
+
+        result: CallResult = self.typer.dispatcher.get_result(
+            location=location,
+            callee=overload,
+            positional=[index],
+            keywords={},
+        )
+        return result.result
+
+    def call(
+        self,
+        method: str,
+        location: Location,
+        call_expr: p.Expr,
+        column: ColumnType,
+        column_expr: p.Expr,
+        positional: list[TypedExpr],
+        keywords: dict[str, TypedExpr],
+    ) -> Type:
+        """Compute the result type of a column's method call
+
+        Args:
+            method (str): the method name
+            location (Location): the call's location
+            call_expr (p.Expr): the call expression
+            column (ColumnType): the column type
+            column_expr (p.Expr): the column expression
+            positional (list[TypedExpr]): the list of positional arguments
+            keywords (dict[str, TypedExpr]): the map of keyword arguments
+
+        Returns:
+            Type: the result type
+        """
+        call: Call = Call(
+            location=location,
+            call_expr=call_expr,
+            column=column,
+            column_expr=column_expr,
+            positional=positional,
+            keywords=keywords,
+        )
+        return self.method_resolver.call(method, call)
+
+    def groupby_call(
+        self,
+        method: str,
+        location: Location,
+        call_expr: p.Expr,
+        groupby: ColumnGroupBy,
+        groupby_expr: p.Expr,
+        positional: list[TypedExpr],
+        keywords: dict[str, TypedExpr],
+    ) -> Type:
+        """Compute the result type of a column group-by's method call
+
+        Args:
+            method (str): the method name
+            location (Location): the call's location
+            call_expr (p.Expr): the call expression
+            groupby (ColumnGroupBy): the column group-by object
+            groupby_expr (p.Expr): the column group-by expression
+            positional (list[TypedExpr]): the list of positional arguments
+            keywords (dict[str, TypedExpr]): the map of keyword arguments
+
+        Returns:
+            Type: the result type
+        """
+        call: GroupByCall = GroupByCall(
+            location=location,
+            call_expr=call_expr,
+            groupby=groupby,
+            groupby_expr=groupby_expr,
+            positional=positional,
+            keywords=keywords,
+        )
+        return self.groupby_method_resolver.call(method, call)
+
+    def get_attribute(self, column: ColumnType, name: str) -> Optional[Type]:
+        """Get the type of a column's attribute
+
+        Args:
+            column (ColumnType): the column type
+            name (str): the attribute's name
+
+        Returns:
+            Optional[Type]: the attribute's type, or `None` if it doesn't exist
+        """
+        types: TypesRegistry = self.typer.types
+        match name:
+            case "ndim" | "size":
+                return types.get_type("int")
+
+            case "shape":
+                return types.tuple_of("int")
+
+            case "T":
+                return column
+
+            case _:
+                return None

midas/checker/frames/column_methods.py

@@ -0,0 +1,683 @@
+from __future__ import annotations
+
+import ast
+from dataclasses import dataclass
+from typing import TYPE_CHECKING, Callable, Optional, TypeAlias, Union
+
+import midas.ast.python as p
+from midas.ast.location import Location
+from midas.checker.dispatcher import CallResult
+from midas.checker.frames.utils import MethodRegistry, method
+from midas.checker.types import (
+    ColumnGroupBy,
+    ColumnType,
+    Function,
+    OverloadedFunction,
+    ParamSpec,
+    TopType,
+    Type,
+    UnitType,
+    UnknownType,
+    unfold_type,
+)
+
+if TYPE_CHECKING:
+    from midas.checker.python import TypedExpr
+
+FormulaOperand: TypeAlias = Union["Formula", str, Type]
+"""
+A operand type in a :data:`Formula`
+
+Must be one of the following:
+- a nested formula
+- a type name (a string)
+- a type instance
+"""
+
+Formula: TypeAlias = Union[Type, tuple[FormulaOperand, str, FormulaOperand]]
+"""
+A formula to compute the output type of a function
+
+Must be either a type, or a tuple containing:
+- a left operand
+- an operation / method name (e.g. `"__add__"`)
+- a right operand
+
+For example, to compute the result of a `mean` function, given the input type `T`:
+```python
+mean_formula = ((T, "__add__", T), "__truediv__", "int")
+```
+"""
+
+
+@dataclass(frozen=True, kw_only=True)
+class Call:
+    """A column method call, implements :class:`utils.MethodCall`"""
+
+    location: Location
+    call_expr: p.Expr
+    column: ColumnType
+    column_expr: p.Expr
+    positional: list[TypedExpr]
+    keywords: dict[str, TypedExpr]
+
+    @property
+    def subject(self) -> TypedExpr:
+        return (self.column_expr, self.column)
+
+
+class ColumnMethodRegistry(MethodRegistry[Call]):
+    """The method registry for column types"""
+
+    def _resolve_formula_operand(self, call: Call, operand: FormulaOperand) -> Type:
+        """Resolve the type of a formula operand
+
+        See :data:`FormulaOperand` for more information on the accepted format
+
+        Args:
+            call (Call): the call that triggered this resolution
+            operand (FormulaOperand): the formula operand
+
+        Returns:
+            Type: the type of the operand
+        """
+        match operand:
+            case str():
+                return self.types.get_type(operand)
+            case (_, _, _):
+                return self._resolve_formula_type(call, operand)
+            case _:
+                return operand
+
+    def _resolve_formula_type(self, call: Call, formula: Formula) -> Type:
+        """Resolve the return type of a formula
+
+        See :data:`Formula` for more information on the accepted format
+
+        Args:
+            call (Call): the call that triggered this resolution
+            formula (Formula): the formula to evaluate
+
+        Returns:
+            Type: the return type of the formula
+        """
+        if not isinstance(formula, tuple):
+            return formula
+
+        op1, operator, op2 = formula
+        op1_type: Type = self._resolve_formula_operand(call, op1)
+        op2_type: Type = self._resolve_formula_operand(call, op2)
+        return self.typer.result_of_binary_op(
+            location=call.location,
+            expr=call.call_expr,
+            left=(call.column_expr, op1_type),
+            right=(call.column_expr, op2_type),
+            method=operator,
+        )
+
+    def _simple_call(self, call: Call, function: Type) -> Type:
+        """Get the result of calling a simple method
+
+        This function is a simple wrapper around :func:`dispatcher.CallDispatcher.get_result`
+        Args:
+            call (Call): the call that triggered this resolution
+            function (Type): the function type
+
+        Returns:
+            Type: the return type
+        """
+        result: CallResult = self.dispatcher.get_result(
+            location=call.location,
+            callee=function,
+            positional=call.positional,
+            keywords=call.keywords,
+        )
+        return result.result
+
+    def _element_binary_op(self, call: Call, method: str) -> tuple[Type, bool]:
+        """Compute the result of an element-wise binary operation
+
+        This function delegates to the inner types for computing the resulting
+        type.
+
+        Args:
+            call (Call): the call that triggered this resolution
+            method (str): the method name
+
+        Returns:
+            tuple[Type, bool]: the resulting type and a boolean indicating
+                whether the operand is a column
+        """
+        if len(call.positional) == 0:
+            return UnknownType(), False
+
+        col_type1: Type = call.column.type
+        operand: TypedExpr = call.positional[0]
+        unfolded_operand: Type = unfold_type(operand[1])
+        col_type2: Type
+
+        column_operand: bool = isinstance(unfolded_operand, ColumnType)
+
+        # Operand is a column -> get the inner type
+        if column_operand:
+            col_type2 = unfolded_operand.type
+        # Otherwise use the operand type itself
+        else:
+            col_type2 = operand[1]
+
+        new_inner_type = self.typer.result_of_binary_op(
+            location=call.location,
+            expr=call.call_expr,
+            left=(call.column_expr, col_type1),
+            right=(operand[0], col_type2),
+            method=method,
+        )
+        return ColumnType(type=new_inner_type), column_operand
+
+    def _element_wise(self, call: Call, method: str) -> Type:
+        """Compute the result of an element-wise method call
+
+        If the call is valid, this method also generates an assertion to check
+        that both operands have the same length at runtime
+
+        Args:
+            call (Call): the call object
+            method (str): the method's name
+
+        Returns:
+            Type: the result type
+        """
+
+        # Build signature with new column type and generic operand
+        returns, column_operand = self._element_binary_op(call, method)
+        signature = Function(
+            params=ParamSpec(
+                mixed=[
+                    Function.Parameter(
+                        pos=0,
+                        name="other",
+                        type=TopType(),
+                        required=True,
+                    ),
+                ],
+            ),
+            returns=returns,
+        )
+
+        # Map arguments and compute result type
+        result: CallResult = self.dispatcher.get_result(
+            location=call.location,
+            callee=signature,
+            positional=call.positional,
+            keywords=call.keywords,
+        )
+        if result.is_valid and column_operand:
+            self._assert_same_length(
+                call.call_expr, call.column_expr, call.positional[0][0]
+            )
+
+        return result.result
+
+    @method()
+    def copy(self, call: Call) -> Type:
+        return self._simple_call(
+            call,
+            Function(
+                params=ParamSpec(
+                    mixed=[
+                        Function.Parameter(
+                            pos=0,
+                            name="deep",
+                            type=self.types.get_type("bool"),
+                            required=False,
+                        )
+                    ]
+                ),
+                returns=call.column,
+            ),
+        )
+
+    @method()
+    def info(self, call: Call) -> Type:
+        def make_overload(memory_usage: Type, required: bool = False) -> Type:
+            return Function(
+                params=ParamSpec(
+                    mixed=[
+                        Function.Parameter(
+                            pos=0,
+                            name="verbose",
+                            type=self.types.get_type("bool"),
+                            required=False,
+                        ),
+                        Function.Parameter(
+                            pos=1,
+                            name="buf",
+                            type=TopType(),
+                            required=False,
+                        ),
+                        Function.Parameter(
+                            pos=2,
+                            name="max_cols",
+                            type=self.types.get_type("int"),
+                            required=False,
+                        ),
+                        Function.Parameter(
+                            pos=3,
+                            name="memory_usage",
+                            type=memory_usage,
+                            required=required,
+                        ),
+                        Function.Parameter(
+                            pos=4,
+                            name="show_counts",
+                            type=self.types.get_type("bool"),
+                            required=False,
+                        ),
+                    ]
+                ),
+                returns=UnitType(),
+            )
+
+        return self._simple_call(
+            call,
+            OverloadedFunction(
+                overloads=[
+                    make_overload(self.types.get_type("bool"), False),
+                    make_overload(self.types.get_type("str"), True),
+                ],
+            ),
+        )
+
+    @method("add", "__add__")
+    def add(self, call: Call) -> Type:
+        return self._element_wise(call, "__add__")
+
+    @method("sub", "__sub__")
+    def sub(self, call: Call) -> Type:
+        return self._element_wise(call, "__sub__")
+
+    @method("mul", "__mul__")
+    def mul(self, call: Call) -> Type:
+        return self._element_wise(call, "__mul__")
+
+    @method("div", "truediv", "__truediv__")
+    def truediv(self, call: Call) -> Type:
+        return self._element_wise(call, "__truediv__")
+
+    @method("floordiv", "__floordiv__")
+    def floordiv(self, call: Call) -> Type:
+        return self._element_wise(call, "__floordiv__")
+
+    @method("mod", "__mod__")
+    def mod(self, call: Call) -> Type:
+        return self._element_wise(call, "__mod__")
+
+    @method("pow", "__pow__")
+    def pow(self, call: Call) -> Type:
+        return self._element_wise(call, "__pow__")
+
+    @method("lt", "__lt__")
+    def lt(self, call: Call) -> Type:
+        return self._element_wise(call, "__lt__")
+
+    @method("gt", "__gt__")
+    def gt(self, call: Call) -> Type:
+        return self._element_wise(call, "__gt__")
+
+    @method("le", "__le__")
+    def le(self, call: Call) -> Type:
+        return self._element_wise(call, "__le__")
+
+    @method("ge", "__ge__")
+    def ge(self, call: Call) -> Type:
+        return self._element_wise(call, "__ge__")
+
+    @method("ne", "__ne__")
+    def ne(self, call: Call) -> Type:
+        return self._element_wise(call, "__ne__")
+
+    @method("eq", "__eq__")
+    def eq(self, call: Call) -> Type:
+        return self._element_wise(call, "__eq__")
+
+    def _aggregate(
+        self,
+        call: Call,
+        kwargs: list[Function.Parameter] = [],
+        *,
+        formula: Optional[Callable[[Type], Formula]] = None,
+    ) -> Type:
+        """Compute the result type of an aggregate method call
+
+        Args:
+            call (Call): the call object
+            kwargs (list[Function.Parameter], optional): a list of extra
+                keyword-only parameters. Defaults to [].
+            formula (Callable[[Type], Formula], optional): optional formula
+                builder function to compute the return type. If set, the function
+                should accept the inner column type and return a formula.
+                If `None`, the result is typed as `Column[Any]`. Defaults to None.
+
+        Returns:
+            Type: the result type
+        """
+
+        returns: Type = ColumnType(type=TopType())
+        if formula:
+            returns = ColumnType(
+                type=self._resolve_formula_type(
+                    call,
+                    formula(call.column.type),
+                )
+            )
+        signature = Function(
+            params=ParamSpec(
+                kw=[
+                    Function.Parameter(
+                        pos=0,
+                        name="axis",
+                        type=TopType(),
+                        required=False,
+                    ),
+                    *kwargs,
+                ],
+            ),
+            returns=returns,
+        )
+
+        result: CallResult = self.dispatcher.get_result(
+            location=call.location,
+            callee=signature,
+            positional=call.positional,
+            keywords=call.keywords,
+        )
+        return result.result
+
+    @method("kurtosis", "kurt")
+    def kurtosis(self, call: Call) -> Type:
+        return self._aggregate(call)
+
+    @method()
+    def max(self, call: Call) -> Type:
+        return self._aggregate(call, formula=lambda t: t)
+
+    @method()
+    def mean(self, call: Call) -> Type:
+        return self._aggregate(
+            call, formula=lambda t: ((t, "__add__", t), "__truediv__", "int")
+        )
+
+    @method()
+    def median(self, call: Call) -> Type:
+        return self._aggregate(call, formula=lambda t: t)
+
+    @method()
+    def min(self, call: Call) -> Type:
+        return self._aggregate(call, formula=lambda t: t)
+
+    @method()
+    def mode(self, call: Call) -> Type:
+        return self._aggregate(call, formula=lambda t: t)
+
+    @method("product", "prod")
+    def product(self, call: Call) -> Type:
+        return self._aggregate(call, formula=lambda t: (t, "__mul__", t))
+
+    @method()
+    def std(self, call: Call) -> Type:
+        return self._aggregate(
+            call,
+            [
+                Function.Parameter(
+                    pos=1,
+                    name="ddof",
+                    type=self.types.get_type("int"),
+                    required=False,
+                )
+            ],
+        )
+
+    @method()
+    def sum(self, call: Call) -> Type:
+        return self._aggregate(call, formula=lambda t: (t, "__add__", t))
+
+    @method()
+    def var(self, call: Call) -> Type:
+        return self._aggregate(
+            call,
+            [
+                Function.Parameter(
+                    pos=1,
+                    name="var",
+                    type=self.types.get_type("int"),
+                    required=False,
+                )
+            ],
+        )
+
+    @method()
+    def head(self, call: Call) -> Type:
+        signature = Function(
+            params=ParamSpec(
+                mixed=[
+                    Function.Parameter(
+                        pos=0,
+                        name="n",
+                        type=self.types.get_type("int"),
+                        required=False,
+                    ),
+                ],
+            ),
+            returns=call.column,
+        )
+
+        result: CallResult = self.dispatcher.get_result(
+            location=call.location,
+            callee=signature,
+            positional=call.positional,
+            keywords=call.keywords,
+        )
+        return result.result
+
+    @method()
+    def tail(self, call: Call) -> Type:
+        signature = Function(
+            params=ParamSpec(
+                mixed=[
+                    Function.Parameter(
+                        pos=0,
+                        name="n",
+                        type=self.types.get_type("int"),
+                        required=False,
+                    ),
+                ],
+            ),
+            returns=call.column,
+        )
+
+        result: CallResult = self.dispatcher.get_result(
+            location=call.location,
+            callee=signature,
+            positional=call.positional,
+            keywords=call.keywords,
+        )
+        return result.result
+
+    @method()
+    def sort_values(self, call: Call) -> Type:
+        str_ = self.types.get_type("str")
+        bool_ = self.types.get_type("bool")
+
+        def make_overload(ascending: Type) -> Function:
+            return Function(
+                params=ParamSpec(
+                    kw=[
+                        Function.Parameter(
+                            pos=0,
+                            name="axis",
+                            type=TopType(),
+                            required=False,
+                        ),
+                        Function.Parameter(
+                            pos=1,
+                            name="ascending",
+                            type=ascending,
+                            required=False,
+                        ),
+                        Function.Parameter(
+                            pos=2,
+                            name="inplace",
+                            type=bool_,
+                            required=False,
+                            unsupported=True,
+                        ),
+                        Function.Parameter(
+                            pos=3,
+                            name="kind",
+                            type=str_,
+                            required=False,
+                        ),
+                        Function.Parameter(
+                            pos=4,
+                            name="na_position",
+                            type=str_,
+                            required=False,
+                        ),
+                        Function.Parameter(
+                            pos=5,
+                            name="ignore_index",
+                            type=bool_,
+                            required=False,
+                        ),
+                        Function.Parameter(
+                            pos=6,
+                            name="key",
+                            type=TopType(),
+                            required=False,
+                        ),
+                    ],
+                ),
+                returns=call.column,
+            )
+
+        list_of = self.types.list_of
+        overloads: list[Type] = [
+            make_overload(bool_),
+            make_overload(bool_),
+            make_overload(list_of(bool_)),
+            make_overload(list_of(bool_)),
+        ]
+
+        result: CallResult = self.dispatcher.get_result(
+            location=call.location,
+            callee=OverloadedFunction(overloads=overloads),
+            positional=call.positional,
+            keywords=call.keywords,
+        )
+        return result.result
+
+    @method()
+    def groupby(self, call: Call) -> Type:
+        bool_: Type = self.types.get_type("bool")
+        function: Function = Function(
+            params=ParamSpec(
+                mixed=[
+                    Function.Parameter(
+                        pos=0,
+                        name="by",
+                        type=TopType(),
+                        required=False,
+                    ),
+                    Function.Parameter(
+                        pos=1,
+                        name="level",
+                        type=TopType(),
+                        required=False,
+                    ),
+                ],
+                kw=[
+                    Function.Parameter(
+                        pos=i + 2,
+                        name=name,
+                        type=bool_,
+                        required=False,
+                    )
+                    for i, name in enumerate(
+                        ["as_index", "sort", "group_keys", "observed", "dropna"]
+                    )
+                ],
+            ),
+            returns=ColumnGroupBy(column=call.column),
+        )
+
+        result: CallResult = self.dispatcher.get_result(
+            location=call.location,
+            callee=function,
+            positional=call.positional,
+            keywords=call.keywords,
+        )
+        return result.result
+
+    def _assert_same_length(self, call_expr: p.Expr, column1: p.Expr, column2: p.Expr):
+        """Generate an assertion to check that two columns have the same length
+
+        Args:
+            call_expr (p.Expr): the call expression, to insert the assertion
+                at the right place
+            column1 (p.Expr): the first column expression
+            column2 (p.Expr): the second column expression
+        """
+        func_name: str = "__midas_column_same_length__"
+
+        # Efficiently compute length
+        # https://stackoverflow.com/a/15943975/11109181
+        def len_of_col(col: ast.expr) -> ast.expr:
+            return ast.Call(
+                func=ast.Name(id="len"),
+                args=[
+                    ast.Attribute(
+                        value=col,
+                        attr="index",
+                    )
+                ],
+                keywords=[],
+            )
+
+        self.assertions.define(
+            func_name,
+            ast.FunctionDef(
+                name=func_name,
+                args=ast.arguments(
+                    posonlyargs=[],
+                    args=[
+                        ast.arg(arg="column1"),
+                        ast.arg(arg="column2"),
+                    ],
+                    kwonlyargs=[],
+                    defaults=[],
+                    kw_defaults=[],
+                ),
+                body=[
+                    ast.Return(
+                        value=ast.Compare(
+                            left=len_of_col(ast.Name(id="column1")),
+                            ops=[ast.Eq()],
+                            comparators=[
+                                len_of_col(ast.Name(id="column2")),
+                            ],
+                        )
+                    )
+                ],
+                decorator_list=[],
+            ),
+        )
+        self.assertions.add(
+            bound_expr=call_expr,
+            inputs=[column1, column2],
+            builder=lambda c1, c2: ast.Call(
+                func=ast.Name(id=func_name),
+                args=[c1, c2],
+                keywords=[],
+            ),
+            message="Columns must have the same length",
+        )

midas/checker/frames/frame_groupby_methods.py

@@ -0,0 +1,109 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import TYPE_CHECKING
+
+import midas.ast.python as p
+from midas.ast.location import Location
+from midas.checker.frames.utils import MethodRegistry, method
+from midas.checker.types import (
+    ColumnGroupBy,
+    ColumnType,
+    DataFrameType,
+    FrameGroupBy,
+    Type,
+    UnknownType,
+)
+
+if TYPE_CHECKING:
+    from midas.checker.python import TypedExpr
+
+
+@dataclass(frozen=True, kw_only=True)
+class Call:
+    """A frame group-by method call, implements :class:`utils.MethodCall`"""
+
+    location: Location
+    call_expr: p.Expr
+    groupby: FrameGroupBy
+    groupby_expr: p.Expr
+    positional: list[TypedExpr]
+    keywords: dict[str, TypedExpr]
+
+    @property
+    def subject(self) -> TypedExpr:
+        return (self.groupby_expr, self.groupby)
+
+
+class FrameGroupByMethodRegistry(MethodRegistry[Call]):
+    """The method registry for frame group-by types"""
+
+    def _aggregate(self, call: Call, method: str) -> Type:
+        """Compute the result type of an aggregate method call
+
+        Args:
+            call (Call): the call object
+            method (str): the method's name
+
+        Returns:
+            Type: the result type
+        """
+        new_columns: list[DataFrameType.Column] = []
+
+        for column in call.groupby.frame.columns:
+            column_groupby: ColumnGroupBy = ColumnGroupBy(column=column.type)
+            result_type: Type = self.typer.call_method(
+                location=call.location,
+                call_expr=call.call_expr,
+                obj=(call.groupby_expr, column_groupby),
+                method_name=method,
+                positional=call.positional,
+                keywords=call.keywords,
+            )
+            if not isinstance(result_type, ColumnType):
+                result_type = ColumnType(type=UnknownType())
+            new_columns.append(
+                DataFrameType.Column(
+                    index=column.index,
+                    name=column.name,
+                    type=result_type,
+                )
+            )
+
+        return DataFrameType(columns=new_columns)
+
+    @method()
+    def kurt(self, call: Call) -> Type:
+        return self._aggregate(call, "kurt")
+
+    @method()
+    def max(self, call: Call) -> Type:
+        return self._aggregate(call, "max")
+
+    @method()
+    def mean(self, call: Call) -> Type:
+        return self._aggregate(call, "mean")
+
+    @method()
+    def median(self, call: Call) -> Type:
+        return self._aggregate(call, "median")
+
+    @method()
+    def min(self, call: Call) -> Type:
+        return self._aggregate(call, "min")
+
+    @method()
+    def prod(self, call: Call) -> Type:
+        return self._aggregate(call, "prod")
+
+    @method()
+    def std(self, call: Call) -> Type:
+        return self._aggregate(call, "std")
+
+    @method()
+    def sum(self, call: Call) -> Type:
+        return self._aggregate(call, "sum")
+
+    @method()
+    def var(self, call: Call) -> Type:
+        return self._aggregate(call, "var")

midas/checker/frames/frame_manager.py

@@ -0,0 +1,386 @@
+from __future__ import annotations
+
+from typing import TYPE_CHECKING, Optional, TypeGuard, cast
+
+import midas.ast.python as p
+from midas.ast.location import Location
+from midas.checker.frames.frame_groupby_methods import Call as GroupByCall
+from midas.checker.frames.frame_groupby_methods import FrameGroupByMethodRegistry
+from midas.checker.frames.frame_methods import Call, FrameMethodRegistry
+from midas.checker.registry import TypesRegistry
+from midas.checker.reporter import FileReporter
+from midas.checker.types import (
+    ColumnGroupBy,
+    ColumnType,
+    DataFrameType,
+    FrameGroupBy,
+    TupleType,
+    Type,
+    UnknownType,
+)
+
+if TYPE_CHECKING:
+    from midas.checker.python import PythonTyper, TypedExpr
+
+
+def is_list_of_literals(exprs: list[p.Expr]) -> TypeGuard[list[p.LiteralExpr]]:
+    """Check whether the given list only contains literal expressions
+
+    Args:
+        exprs (list[p.Expr]): the list to check
+
+    Returns:
+        TypeGuard[list[p.LiteralExpr]]: whether `exprs` only contains literal expressions
+    """
+    return all(isinstance(expr, p.LiteralExpr) for expr in exprs)
+
+
+class FrameManager:
+    """Helper class to handle methods and subscripts on frame types"""
+
+    def __init__(self, typer: PythonTyper) -> None:
+        self.typer: PythonTyper = typer
+        self.method_resolver: FrameMethodRegistry = FrameMethodRegistry(self.typer)
+        self.groupby_method_resolver: FrameGroupByMethodRegistry = (
+            FrameGroupByMethodRegistry(self.typer)
+        )
+
+    def assign(
+        self,
+        reporter: FileReporter,
+        location: Location,
+        frame: DataFrameType,
+        index: p.Expr,
+        value_type: Type,
+    ) -> Type:
+        """Compute the new frame type after assigning a value to an index
+
+        Args:
+            reporter (FileReporter): the file reporter to use for diagnostics
+            location (Location): the assignment's location
+            frame (DataFrameType): the frame type
+            index (p.Expr): the index expression
+            value_type (Type): the assigned value
+
+        Returns:
+            Type: the resulting frame type
+        """
+        match index:
+            case p.LiteralExpr(value=str() as name):
+                return self.assign_column(reporter, location, frame, name, value_type)
+
+            case p.ListExpr(items=indices) if is_list_of_literals(indices) and all(
+                isinstance(index.value, str) for index in indices
+            ):
+                names: list[str] = [cast(str, index.value) for index in indices]
+
+                if not isinstance(value_type, TupleType):
+                    reporter.error(
+                        location,
+                        f"Cannot assign {type} to dataframe columns. Must be a tuple of columns",
+                    )
+                    return UnknownType()
+
+                if len(names) != len(value_type.items):
+                    reporter.error(
+                        location,
+                        f"Wrong number of columns. Cannot assign {len(value_type.items)} to {len(names)} targets",
+                    )
+                    return UnknownType()
+
+                new_frame: Type = frame
+                for name, value in zip(names, value_type.items):
+                    new_frame = self.assign_column(
+                        reporter,
+                        location,
+                        new_frame,
+                        name,
+                        value,
+                    )
+                    if not isinstance(new_frame, DataFrameType):
+                        return new_frame
+                return new_frame
+
+            case _:
+                reporter.error(
+                    location, f"Invalid index type {index} on {frame} (assignment)"
+                )
+                return UnknownType()
+
+    def assign_column(
+        self,
+        reporter: FileReporter,
+        location: Location,
+        frame: DataFrameType,
+        name: str,
+        type: Type,
+    ) -> Type:
+        """Compute the new frame type after assigning a single value to a column
+
+        Args:
+            reporter (FileReporter): the file reporter to use for diagnostics
+            location (Location): the assignment's location
+            frame (DataFrameType): the frame type
+            name (str): the column name
+            type (Type): the assigned value type
+
+        Returns:
+            Type: the resulting frame type
+        """
+        if not isinstance(type, ColumnType):
+            reporter.error(
+                location,
+                f"Cannot assign {type} to dataframe column. Must be a ColumnType",
+            )
+            return self._set_column(frame, name, ColumnType(type=UnknownType()))
+        return self._set_column(frame, name, type)
+
+    def get(
+        self,
+        reporter: FileReporter,
+        location: Location,
+        frame: DataFrameType,
+        index: p.Expr,
+    ) -> Type:
+        """Compute the type of a subscript access
+
+        Args:
+            reporter (FileReporter): the file reporter to use for diagnostics
+            location (Location): the subscript's location
+            frame (DataFrameType): the frame type
+            index (p.Expr): the index expression
+
+        Returns:
+            Type: the resulting type
+        """
+        match index:
+            case p.LiteralExpr(value=str() as name):
+                column: Optional[ColumnType] = FrameManager._get_column(frame, name)
+                if column is None:
+                    reporter.error(location, f"Unknown column '{name}' on {frame}")
+                    return UnknownType()
+                return column
+
+            case p.ListExpr(items=indices) if is_list_of_literals(indices) and all(
+                isinstance(index.value, str) for index in indices
+            ):
+                names: list[str] = [cast(str, index.value) for index in indices]
+                columns: list[ColumnType] = []
+                for name in names:
+                    column: Optional[ColumnType] = FrameManager._get_column(frame, name)
+                    if column is None:
+                        reporter.error(location, f"Unknown column '{name}' on {frame}")
+                        return UnknownType()
+                    columns.append(column)
+                return TupleType(items=tuple(columns))
+
+            case _:
+                reporter.error(
+                    location, f"Invalid index type {index} on {frame} (access)"
+                )
+                return UnknownType()
+
+    def groupby_get(
+        self,
+        reporter: FileReporter,
+        location: Location,
+        groupby: FrameGroupBy,
+        index: p.Expr,
+    ) -> Type:
+        """Compute the type of a subscript access on a frame group-by object
+
+        Args:
+            reporter (FileReporter): the file reporter to use for diagnostics
+            location (Location): the subscript's location
+            groupby (FrameGroupBy): the group-by object
+            index (p.Expr): the index expression
+
+        Returns:
+            Type: the resulting type
+        """
+        result: Type = self.get(reporter, location, groupby.frame, index)
+        match result:
+            case ColumnType():
+                result = ColumnGroupBy(column=result)
+            case TupleType(items=columns):
+                result = TupleType(
+                    items=tuple(
+                        ColumnGroupBy(column=cast(ColumnType, column))
+                        for column in columns
+                    )
+                )
+        return result
+
+    @classmethod
+    def _set_column(
+        cls, frame: DataFrameType, name: str, column: ColumnType
+    ) -> DataFrameType:
+        """Set a frame's column to the given type
+
+        Args:
+            frame (DataFrameType): the frame type
+            name (str): the column's name
+            column (ColumnType): the new column's type
+
+        Returns:
+            DataFrameType: the new frame type
+        """
+        new_columns: list[DataFrameType.Column] = []
+        index: int = len(frame.columns)
+        replace: bool = False
+        for i, col in enumerate(frame.columns):
+            if col.name == name:
+                index = i
+                replace = True
+                # TODO: check column type here to prevent changing it
+            new_columns.append(col)
+
+        new_col: DataFrameType.Column = DataFrameType.Column(
+            index=index,
+            name=name,
+            type=column,
+        )
+        if replace:
+            new_columns[index] = new_col
+        else:
+            new_columns.append(new_col)
+
+        return DataFrameType(columns=new_columns)
+
+    @classmethod
+    def _set_columns(
+        cls, frame: DataFrameType, names: list[str], columns: list[ColumnType]
+    ) -> DataFrameType:
+        """Set multiple columns of a frame to the given types
+
+        Args:
+            frame (DataFrameType): the frame type
+            names (list[str]): the column names
+            columns (list[ColumnType]): the new column types
+
+        Returns:
+            DataFrameType: the new frame type
+        """
+        for name, col in zip(names, columns):
+            frame = cls._set_column(frame, name, col)
+        return frame
+
+    @classmethod
+    def _get_column(cls, frame: DataFrameType, name: str) -> Optional[ColumnType]:
+        """Get a column's type by name
+
+        Args:
+            frame (DataFrameType): the frame type
+            name (str): the column's name
+
+        Returns:
+            Optional[ColumnType]: the column's type, or `None` if it doesn't exist
+        """
+        for col in frame.columns:
+            if col.name == name:
+                return col.type
+        return None
+
+    @classmethod
+    def _get_columns(
+        cls, frame: DataFrameType, names: list[str]
+    ) -> list[Optional[ColumnType]]:
+        """Get multiple column types by name
+
+        Args:
+            frame (DataFrameType): the frame type
+            names (list[str]): the column names
+
+        Returns:
+            list[Optional[ColumnType]]: the column types (see :func:`_get_column`)
+        """
+        return [cls._get_column(frame, name) for name in names]
+
+    def call(
+        self,
+        method: str,
+        location: Location,
+        call_expr: p.Expr,
+        frame: DataFrameType,
+        frame_expr: p.Expr,
+        positional: list[TypedExpr],
+        keywords: dict[str, TypedExpr],
+    ) -> Type:
+        """Compute the result type of a frame's method call
+
+        Args:
+            method (str): the method name
+            location (Location): the call's location
+            call_expr (p.Expr): the call expression
+            frame (DataFrameType): the frame type
+            frame_expr (p.Expr): the frame expression
+            positional (list[TypedExpr]): the list of positional arguments
+            keywords (dict[str, TypedExpr]): the map of keyword arguments
+
+        Returns:
+            Type: the result type
+        """
+        call: Call = Call(
+            location=location,
+            call_expr=call_expr,
+            frame=frame,
+            frame_expr=frame_expr,
+            positional=positional,
+            keywords=keywords,
+        )
+        return self.method_resolver.call(method, call)
+
+    def groupby_call(
+        self,
+        method: str,
+        location: Location,
+        call_expr: p.Expr,
+        groupby: FrameGroupBy,
+        groupby_expr: p.Expr,
+        positional: list[TypedExpr],
+        keywords: dict[str, TypedExpr],
+    ) -> Type:
+        """Compute the result type of a frame group-by's method call
+
+        Args:
+            method (str): the method name
+            location (Location): the call's location
+            call_expr (p.Expr): the call expression
+            groupby (FrameGroupBy): the frame group-by object
+            groupby_expr (p.Expr): the frame group-by expression
+            positional (list[TypedExpr]): the list of positional arguments
+            keywords (dict[str, TypedExpr]): the map of keyword arguments
+
+        Returns:
+            Type: the result type
+        """
+        call: GroupByCall = GroupByCall(
+            location=location,
+            call_expr=call_expr,
+            groupby=groupby,
+            groupby_expr=groupby_expr,
+            positional=positional,
+            keywords=keywords,
+        )
+        return self.groupby_method_resolver.call(method, call)
+
+    def get_attribute(self, frame: DataFrameType, name: str) -> Optional[Type]:
+        """Get the type of a frame's attribute
+
+        Args:
+            frame (DataFrameType): the frame type
+            name (str): the attribute's name
+
+        Returns:
+            Optional[Type]: the attribute's type, or `None` if it doesn't exist
+        """
+        types: TypesRegistry = self.typer.types
+        match name:
+            case "ndim" | "size":
+                return types.get_type("int")
+
+            case "shape":
+                return types.tuple_of("int", "int")
+
+            case _:
+                return None

midas/checker/frames/frame_methods.py

@@ -0,0 +1,700 @@
+from __future__ import annotations
+
+import ast
+from dataclasses import dataclass
+from typing import TYPE_CHECKING, Optional
+
+import midas.ast.python as p
+from midas.ast.location import Location
+from midas.checker.dispatcher import CallResult
+from midas.checker.frames.utils import MethodRegistry, method
+from midas.checker.types import (
+    ColumnType,
+    DataFrameType,
+    FrameGroupBy,
+    Function,
+    OverloadedFunction,
+    ParamSpec,
+    TopType,
+    Type,
+    UnitType,
+    UnknownType,
+    unfold_type,
+)
+
+if TYPE_CHECKING:
+    from midas.checker.python import TypedExpr
+
+
+@dataclass(frozen=True, kw_only=True)
+class Call:
+    """A frame method call, implements :class:`utils.MethodCall`"""
+
+    location: Location
+    call_expr: p.Expr
+    frame: DataFrameType
+    frame_expr: p.Expr
+    positional: list[TypedExpr]
+    keywords: dict[str, TypedExpr]
+
+    @property
+    def subject(self) -> TypedExpr:
+        return (self.frame_expr, self.frame)
+
+
+class FrameMethodRegistry(MethodRegistry[Call]):
+    """The method registry for frame types"""
+
+    def _simple_call(self, call: Call, function: Type) -> Type:
+        """Get the result of calling a simple method
+
+        This function is a simple wrapper around :func:`dispatcher.CallDispatcher.get_result`
+        Args:
+            call (Call): the call that triggered this resolution
+            function (Type): the function type
+
+        Returns:
+            Type: the return type
+        """
+        result: CallResult = self.dispatcher.get_result(
+            location=call.location,
+            callee=function,
+            positional=call.positional,
+            keywords=call.keywords,
+        )
+        return result.result
+
+    def _get_method_result(
+        self,
+        call: Call,
+        column1: ColumnType,
+        column2: ColumnType,
+        method: str,
+    ) -> ColumnType:
+        """Get the result of calling a method on a column, passing a second
+
+        This function delegates to the main typer the resolution of the method
+        member, as well as computing the result type. Because we don't have any
+        AST expression for the individual columns, the frame expressions are
+        used instead.
+
+        Args:
+            call (Call): the call that triggered this resolution
+            column1 (ColumnType): the first column, i.e. left operand
+            column2 (ColumnType): the second column, i.e. right operand
+            method (str): the method name
+
+        Returns:
+            ColumnType: the resulting column.
+                If the operation is invalid / doesn't exist,
+                `ColumnType(type=UnknownType())` is returned
+        """
+
+        result: Type = self.typer.result_of_binary_op(
+            location=call.location,
+            expr=call.call_expr,
+            left=(call.frame_expr, column1),
+            right=(call.positional[0][0], column2),
+            method=method,
+        )
+
+        if not isinstance(result, ColumnType):
+            return ColumnType(type=UnknownType())
+        return result
+
+    def _element_binary_op(self, call: Call, method: str) -> tuple[Type, bool]:
+        """Compute the result of an element-wise binary operation
+
+        This function delegates to the matching columns for computing resulting
+        types. Any column only present in one of the frames is forwarded as a
+        generic `ColumnType(type=UnknownType())`. Columns only in the second
+        frame are append at the end of the schema.
+
+        Args:
+            call (Call): the call that triggered this resolution
+            method (str): the method name
+
+        Returns:
+            tuple[Type, bool]: the resulting type and a boolean indicating
+                whether the operand is a frame
+        """
+
+        if len(call.positional) == 0:
+            return UnknownType(), False
+
+        operand: TypedExpr = call.positional[0]
+        new_columns: list[DataFrameType.Column] = []
+
+        by_name: dict[str, DataFrameType.Column] = {}
+        frame2: Optional[DataFrameType] = None
+        # Get map of operand's columns by name, if the operand is a dataframe
+        unfolded_other: Type = unfold_type(operand[1])
+        frame_operand: bool = isinstance(unfolded_other, DataFrameType)
+        if frame_operand:
+            frame2 = unfolded_other
+            by_name = {col.name: col for col in frame2.columns if col.name is not None}
+
+        # Compute new schema:
+        # Step 1: for all columns in frame1:
+        #  - if present in frame2 -> delegate operation to columns
+        #  - if not -> add to schema as unknown
+        in_frame1: set[str] = set()
+        for column in call.frame.columns:
+            if column.name is not None:
+                in_frame1.add(column.name)
+
+            col_type1: ColumnType = column.type
+            col_type: ColumnType = ColumnType(type=UnknownType())
+
+            col_type2: Optional[ColumnType] = None
+
+            # Operand is a frame -> lookup column with the same name
+            if frame2 is not None:
+                if column.name in by_name:
+                    column2 = by_name[column.name]
+                    col_type2 = column2.type
+
+            # Operand is not a frame -> scalar operation -> ad-hoc column
+            else:
+                col_type2 = ColumnType(type=operand[1])
+
+            if col_type2 is not None:
+                col_type = self._get_method_result(call, col_type1, col_type2, method)
+
+            new_column = DataFrameType.Column(
+                index=column.index,
+                name=column.name,
+                type=col_type,
+            )
+            new_columns.append(new_column)
+
+        # Step 2: for all columns in frame2
+        #  - if not in frame1 -> add to schema as unknown
+        if frame2 is not None:
+            for column in frame2.columns:
+                if column.name in in_frame1:
+                    continue
+                new_columns.append(
+                    DataFrameType.Column(
+                        index=len(new_columns),
+                        name=column.name,
+                        type=ColumnType(type=UnknownType()),
+                    )
+                )
+
+        return DataFrameType(columns=new_columns), frame_operand
+
+    def _element_wise(self, call: Call, method: str) -> Type:
+        """Compute the result of an element-wise method call
+
+        If the call is valid, this method also generates an assertion to check
+        that both operands have the same length at runtime
+
+        Args:
+            call (Call): the call object
+            method (str): the method's name
+
+        Returns:
+            Type: the result type
+        """
+        # TODO: support sequence, Series, dict operand
+        returns, frame_operand = self._element_binary_op(call, method)
+
+        # Build signature with new schema and generic operand
+        signature = Function(
+            params=ParamSpec(
+                mixed=[
+                    Function.Parameter(
+                        pos=0,
+                        name="other",
+                        type=TopType(),
+                        required=True,
+                    ),
+                ],
+            ),
+            returns=returns,
+        )
+
+        # Map arguments and compute result type
+        result: CallResult = self.dispatcher.get_result(
+            location=call.location,
+            callee=signature,
+            positional=call.positional,
+            keywords=call.keywords,
+        )
+        if result.is_valid and frame_operand:
+            self._assert_same_length(
+                call.call_expr, call.frame_expr, call.positional[0][0]
+            )
+
+        return result.result
+
+    @method()
+    def copy(self, call: Call) -> Type:
+        return self._simple_call(
+            call,
+            Function(
+                params=ParamSpec(
+                    mixed=[
+                        Function.Parameter(
+                            pos=0,
+                            name="deep",
+                            type=self.types.get_type("bool"),
+                            required=False,
+                        )
+                    ]
+                ),
+                returns=call.frame,
+            ),
+        )
+
+    @method()
+    def info(self, call: Call) -> Type:
+        def make_overload(memory_usage: Type, required: bool = False) -> Type:
+            return Function(
+                params=ParamSpec(
+                    mixed=[
+                        Function.Parameter(
+                            pos=0,
+                            name="verbose",
+                            type=self.types.get_type("bool"),
+                            required=False,
+                        ),
+                        Function.Parameter(
+                            pos=1,
+                            name="buf",
+                            type=TopType(),
+                            required=False,
+                        ),
+                        Function.Parameter(
+                            pos=2,
+                            name="max_cols",
+                            type=self.types.get_type("int"),
+                            required=False,
+                        ),
+                        Function.Parameter(
+                            pos=3,
+                            name="memory_usage",
+                            type=memory_usage,
+                            required=required,
+                        ),
+                        Function.Parameter(
+                            pos=4,
+                            name="show_counts",
+                            type=self.types.get_type("bool"),
+                            required=False,
+                        ),
+                    ]
+                ),
+                returns=UnitType(),
+            )
+
+        return self._simple_call(
+            call,
+            OverloadedFunction(
+                overloads=[
+                    make_overload(self.types.get_type("bool"), False),
+                    make_overload(self.types.get_type("str"), True),
+                ],
+            ),
+        )
+
+    @method("add", "__add__")
+    def add(self, call: Call) -> Type:
+        return self._element_wise(call, "__add__")
+
+    @method("sub", "__sub__")
+    def sub(self, call: Call) -> Type:
+        return self._element_wise(call, "__sub__")
+
+    @method("mul", "__mul__")
+    def mul(self, call: Call) -> Type:
+        return self._element_wise(call, "__mul__")
+
+    @method("div", "truediv", "__truediv__")
+    def truediv(self, call: Call) -> Type:
+        return self._element_wise(call, "__truediv__")
+
+    @method("floordiv", "__floordiv__")
+    def floordiv(self, call: Call) -> Type:
+        return self._element_wise(call, "__floordiv__")
+
+    @method("mod", "__mod__")
+    def mod(self, call: Call) -> Type:
+        return self._element_wise(call, "__mod__")
+
+    @method("pow", "__pow__")
+    def pow(self, call: Call) -> Type:
+        return self._element_wise(call, "__pow__")
+
+    @method("lt", "__lt__")
+    def lt(self, call: Call) -> Type:
+        return self._element_wise(call, "__lt__")
+
+    @method("gt", "__gt__")
+    def gt(self, call: Call) -> Type:
+        return self._element_wise(call, "__gt__")
+
+    @method("le", "__le__")
+    def le(self, call: Call) -> Type:
+        return self._element_wise(call, "__le__")
+
+    @method("ge", "__ge__")
+    def ge(self, call: Call) -> Type:
+        return self._element_wise(call, "__ge__")
+
+    @method("ne", "__ne__")
+    def ne(self, call: Call) -> Type:
+        return self._element_wise(call, "__ne__")
+
+    @method("eq", "__eq__")
+    def eq(self, call: Call) -> Type:
+        return self._element_wise(call, "__eq__")
+
+    def _aggregate(self, call: Call, kwargs: list[Function.Parameter] = []) -> Type:
+        """Compute the result type of an aggregate method call
+
+        Args:
+            call (Call): the call object
+            kwargs (list[Function.Parameter], optional): a list of extra
+                keyword-only parameters. Defaults to [].
+
+        Returns:
+            Type: the result type
+        """
+        with_axis = Function(
+            params=ParamSpec(
+                kw=[
+                    Function.Parameter(
+                        pos=0,
+                        name="axis",
+                        type=self.types.get_type("int"),
+                        required=False,
+                    ),
+                    *kwargs,
+                ],
+            ),
+            returns=ColumnType(type=TopType()),
+        )
+        without_axis = Function(
+            params=ParamSpec(
+                kw=[
+                    Function.Parameter(
+                        pos=0,
+                        name="axis",
+                        type=self.types.get_type("None"),
+                        required=True,
+                    ),
+                    *kwargs,
+                ],
+            ),
+            returns=TopType(),
+        )
+        overload = OverloadedFunction(
+            overloads=[
+                with_axis,
+                without_axis,
+            ]
+        )
+
+        result: CallResult = self.dispatcher.get_result(
+            location=call.location,
+            callee=overload,
+            positional=call.positional,
+            keywords=call.keywords,
+        )
+        return result.result
+
+    @method("kurtosis", "kurt")
+    def kurtosis(self, call: Call) -> Type:
+        return self._aggregate(call)
+
+    @method()
+    def max(self, call: Call) -> Type:
+        return self._aggregate(call)
+
+    @method()
+    def mean(self, call: Call) -> Type:
+        return self._aggregate(call)
+
+    @method()
+    def median(self, call: Call) -> Type:
+        return self._aggregate(call)
+
+    @method()
+    def min(self, call: Call) -> Type:
+        return self._aggregate(call)
+
+    @method()
+    def mode(self, call: Call) -> Type:
+        return self._aggregate(call)
+
+    @method("product", "prod")
+    def product(self, call: Call) -> Type:
+        return self._aggregate(call)
+
+    @method()
+    def std(self, call: Call) -> Type:
+        return self._aggregate(
+            call,
+            [
+                Function.Parameter(
+                    pos=1,
+                    name="ddof",
+                    type=self.types.get_type("int"),
+                    required=False,
+                )
+            ],
+        )
+
+    @method()
+    def sum(self, call: Call) -> Type:
+        return self._aggregate(call)
+
+    @method()
+    def var(self, call: Call) -> Type:
+        return self._aggregate(
+            call,
+            [
+                Function.Parameter(
+                    pos=1,
+                    name="var",
+                    type=self.types.get_type("int"),
+                    required=False,
+                )
+            ],
+        )
+
+    @method()
+    def head(self, call: Call) -> Type:
+        signature = Function(
+            params=ParamSpec(
+                mixed=[
+                    Function.Parameter(
+                        pos=0,
+                        name="n",
+                        type=self.types.get_type("int"),
+                        required=False,
+                    ),
+                ],
+            ),
+            returns=call.frame,
+        )
+
+        result: CallResult = self.dispatcher.get_result(
+            location=call.location,
+            callee=signature,
+            positional=call.positional,
+            keywords=call.keywords,
+        )
+        return result.result
+
+    @method()
+    def tail(self, call: Call) -> Type:
+        signature = Function(
+            params=ParamSpec(
+                mixed=[
+                    Function.Parameter(
+                        pos=0,
+                        name="n",
+                        type=self.types.get_type("int"),
+                        required=False,
+                    ),
+                ],
+            ),
+            returns=call.frame,
+        )
+
+        result: CallResult = self.dispatcher.get_result(
+            location=call.location,
+            callee=signature,
+            positional=call.positional,
+            keywords=call.keywords,
+        )
+        return result.result
+
+    @method()
+    def sort_values(self, call: Call) -> Type:
+        str_ = self.types.get_type("str")
+        bool_ = self.types.get_type("bool")
+
+        def make_overload(by: Type, ascending: Type) -> Function:
+            return Function(
+                params=ParamSpec(
+                    mixed=[
+                        Function.Parameter(
+                            pos=0,
+                            name="by",
+                            type=by,
+                            required=True,
+                        ),
+                    ],
+                    kw=[
+                        Function.Parameter(
+                            pos=1,
+                            name="axis",
+                            type=TopType(),
+                            required=False,
+                        ),
+                        Function.Parameter(
+                            pos=2,
+                            name="ascending",
+                            type=ascending,
+                            required=False,
+                        ),
+                        Function.Parameter(
+                            pos=3,
+                            name="inplace",
+                            type=bool_,
+                            required=False,
+                            unsupported=True,
+                        ),
+                        Function.Parameter(
+                            pos=4,
+                            name="kind",
+                            type=str_,
+                            required=False,
+                        ),
+                        Function.Parameter(
+                            pos=5,
+                            name="na_position",
+                            type=str_,
+                            required=False,
+                        ),
+                        Function.Parameter(
+                            pos=6,
+                            name="ignore_index",
+                            type=bool_,
+                            required=False,
+                        ),
+                        Function.Parameter(
+                            pos=7,
+                            name="key",
+                            type=TopType(),
+                            required=False,
+                        ),
+                    ],
+                ),
+                returns=call.frame,
+            )
+
+        list_of = self.types.list_of
+        overloads: list[Type] = [
+            make_overload(by=str_, ascending=bool_),
+            make_overload(by=list_of(str_), ascending=bool_),
+            make_overload(by=str_, ascending=list_of(bool_)),
+            make_overload(by=list_of(str_), ascending=list_of(bool_)),
+        ]
+
+        # TODO: check that literal strings in `by` are valid columns
+        result: CallResult = self.dispatcher.get_result(
+            location=call.location,
+            callee=OverloadedFunction(overloads=overloads),
+            positional=call.positional,
+            keywords=call.keywords,
+        )
+        return result.result
+
+    @method()
+    def groupby(self, call: Call) -> Type:
+        bool_: Type = self.types.get_type("bool")
+        function: Function = Function(
+            params=ParamSpec(
+                mixed=[
+                    Function.Parameter(
+                        pos=0,
+                        name="by",
+                        type=TopType(),
+                        required=False,
+                    ),
+                    Function.Parameter(
+                        pos=1,
+                        name="level",
+                        type=TopType(),
+                        required=False,
+                    ),
+                ],
+                kw=[
+                    Function.Parameter(
+                        pos=i + 2,
+                        name=name,
+                        type=bool_,
+                        required=False,
+                    )
+                    for i, name in enumerate(
+                        ["as_index", "sort", "group_keys", "observed", "dropna"]
+                    )
+                ],
+            ),
+            returns=FrameGroupBy(frame=call.frame),
+        )
+
+        result: CallResult = self.dispatcher.get_result(
+            location=call.location,
+            callee=function,
+            positional=call.positional,
+            keywords=call.keywords,
+        )
+        return result.result
+
+    def _assert_same_length(self, call_expr: p.Expr, frame1: p.Expr, frame2: p.Expr):
+        """Generate an assertion to check that two frames have the same length
+
+        Args:
+            call_expr (p.Expr): the call expression, to insert the assertion
+                at the right place
+            frame1 (p.Expr): the first frame expression
+            frame2 (p.Expr): the second frame expression
+        """
+        func_name: str = "__midas_frame_same_length__"
+
+        # Efficiently compute length
+        # https://stackoverflow.com/a/15943975/11109181
+        def len_of_df(df: ast.expr) -> ast.expr:
+            return ast.Call(
+                func=ast.Name(id="len"),
+                args=[
+                    ast.Attribute(
+                        value=df,
+                        attr="index",
+                    )
+                ],
+                keywords=[],
+            )
+
+        self.assertions.define(
+            func_name,
+            ast.FunctionDef(
+                name=func_name,
+                args=ast.arguments(
+                    posonlyargs=[],
+                    args=[
+                        ast.arg(arg="frame1"),
+                        ast.arg(arg="frame2"),
+                    ],
+                    kwonlyargs=[],
+                    defaults=[],
+                    kw_defaults=[],
+                ),
+                body=[
+                    ast.Return(
+                        value=ast.Compare(
+                            left=len_of_df(ast.Name(id="frame1")),
+                            ops=[ast.Eq()],
+                            comparators=[len_of_df(ast.Name(id="frame2"))],
+                        )
+                    )
+                ],
+                decorator_list=[],
+            ),
+        )
+        self.assertions.add(
+            bound_expr=call_expr,
+            inputs=[frame1, frame2],
+            builder=lambda f1, f2: ast.Call(
+                func=ast.Name(id=func_name),
+                args=[f1, f2],
+                keywords=[],
+            ),
+            message="DataFrames must have the same length",
+        )

midas/checker/frames/utils.py

@@ -0,0 +1,129 @@
+from __future__ import annotations
+
+from typing import (
+    TYPE_CHECKING,
+    Any,
+    Callable,
+    Generic,
+    Optional,
+    Protocol,
+    Self,
+    TypeVar,
+)
+
+import midas.ast.python as p
+from midas.ast.location import Location
+from midas.checker.dispatcher import CallDispatcher
+from midas.checker.registry import TypesRegistry
+from midas.checker.reporter import FileReporter
+from midas.checker.types import Type, UnknownType
+from midas.generator.collector import AssertionCollector
+
+if TYPE_CHECKING:
+    from midas.checker.python import PythonTyper, TypedExpr
+
+
+class _MethodRegistryMeta(type):
+    """Meta-class for :class:`MethodRegistry`
+
+    Collects methods marked with the :func:`method` decorator into a dictionary
+    named `_methods` on the class itself
+    """
+
+    _methods: dict[str, Callable[..., Type]] = {}
+
+    def __new__(
+        cls,
+        name: str,
+        bases: tuple[type, ...],
+        namespace: dict[str, Any],
+    ):
+        new_class = super().__new__(cls, name, bases, namespace)
+        new_class._methods = {}
+        for attr in namespace.values():
+            if callable(attr) and hasattr(attr, "__method_names__"):
+                for name in attr.__method_names__:  # type: ignore
+                    new_class._methods[name] = attr  # type: ignore
+        return new_class
+
+
+class MethodCall(Protocol):
+    """A method call object
+
+    Must have at least `location`, `call_expr` and `subject` properties
+    """
+
+    @property
+    def location(self) -> Location: ...
+
+    @property
+    def call_expr(self) -> p.Expr: ...
+
+    @property
+    def subject(self) -> TypedExpr: ...
+
+
+T = TypeVar("T", bound=MethodCall)
+
+
+class MethodRegistry(Generic[T], metaclass=_MethodRegistryMeta):
+    """A registry of methods"""
+
+    def __init__(self, typer: PythonTyper) -> None:
+        self.typer: PythonTyper = typer
+
+    @property
+    def reporter(self) -> FileReporter:
+        return self.typer.reporter
+
+    @property
+    def types(self) -> TypesRegistry:
+        return self.typer.types
+
+    @property
+    def dispatcher(self) -> CallDispatcher[p.Expr]:
+        return self.typer.dispatcher
+
+    @property
+    def assertions(self) -> AssertionCollector:
+        return self.typer.assertions
+
+    def call(self, method: str, call: T) -> Type:
+        """Compute the result type of a call to the given method
+
+        Args:
+            method (str): the method's name
+            call (T): the call
+
+        Returns:
+            Type: the result type
+        """
+        func: Optional[Callable[[Self, T], Type]] = self._methods.get(method)
+        if func is None:
+            self.reporter.warning(
+                call.location, f"Unknown method {method} on {call.subject[1]}"
+            )
+            return UnknownType()
+        return func(self, call)
+
+
+_Self = TypeVar("_Self", bound=MethodRegistry[Any])
+Method = Callable[[_Self, T], Type]
+
+
+def method(*names: str) -> Callable[[Method[_Self, T]], Method[_Self, T]]:
+    """Simple decorator to mark a method as part of the registry
+
+    Args:
+        names (str): names by which the method can be called. If left empty, the
+            Python method's name will be used
+    """
+
+    def wrapper(func: Method[_Self, T]) -> Method[_Self, T]:
+        names_: tuple[str, ...] = names
+        if len(names_) == 0:
+            names_ = (func.__name__,)
+        setattr(func, "__method_names__", names_)
+        return func
+
+    return wrapper

midas/checker/midas.py

@@ -1,72 +1,48 @@
 import logging
-from dataclasses import dataclass
 from pathlib import Path
 from typing import Optional
 
 import midas.ast.midas as m
 from midas.ast.location import Location
 from midas.checker.builtins import define_builtins
+from midas.checker.dispatcher import CallDispatcher, CallResult
 from midas.checker.environment import Environment
 from midas.checker.operators import MIDAS_BINARY_METHODS, MIDAS_UNARY_METHODS
 from midas.checker.preamble import Preamble
 from midas.checker.registry import TypesRegistry
 from midas.checker.reporter import FileReporter, Reporter
 from midas.checker.types import (
-    AliasType,
-    AppliedType,
+    ColumnType,
     ComplexType,
     ConstraintType,
+    DataFrameType,
+    DerivedType,
     ExtensionType,
     Function,
     GenericType,
-    OverloadedFunction,
+    ParamSpec,
     Predicate,
     Type,
     TypeVar,
     UnknownType,
-    unfold_type,
 )
 from midas.checker.variance import VarianceInferrer
 from midas.lexer.midas import MidasLexer
-from midas.lexer.token import Token
+from midas.lexer.token import Token, TokenType
 from midas.parser.midas import MidasParser
 
 
-@dataclass(frozen=True, kw_only=True)
-class TypedParamSpec:
-    pos: list[Function.Argument]
-    mixed: list[Function.Argument]
-    kw: list[Function.Argument]
-
-
-TypedExpr = tuple[m.Expr, Type]
-
-
-class ReturnException(Exception):
-    pass
-
-
-@dataclass(frozen=True, kw_only=True)
-class MappedArgument:
-    expr: m.Expr
-    type: Type
-    argument: Function.Argument
-
-
-@dataclass(frozen=True, kw_only=True)
-class OverloadCandidate:
-    function: Function
-    mapped: list[MappedArgument]
-
-
 class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[Type], m.Type.Visitor[Type]):
     """A resolver which evaluates Midas type definitions and build a registry"""
 
     def __init__(self, types: TypesRegistry, reporter: Reporter) -> None:
         self.logger: logging.Logger = logging.getLogger("MidasTyper")
         self.reporter: FileReporter = reporter.for_file(None)
-
         self.types: TypesRegistry = types
+        self.dispatcher: CallDispatcher[m.Expr] = CallDispatcher[m.Expr](
+            self.types, self.reporter
+        )
+
         self._local_variables: dict[str, TypeVar] = {}
 
         self._predicate_params: dict[str, Type] = {}
@@ -81,8 +57,25 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[Type], m.Type.Visitor[Type
 
         self._preamble: Environment = Preamble(self.types)
 
+    def set_reporter(self, reporter: FileReporter):
+        """Set the file reporter to use for diagnostics
+
+        Args:
+            reporter (FileReporter): the file reporter
+        """
+        self.reporter = reporter
+        self.dispatcher.set_reporter(reporter)
+
     def process(self, source: str, path: Optional[str]):
-        self.reporter = self.reporter.for_file(path)
+        """Process some Midas source code
+
+        Args:
+            source (str): the Midas source code
+            path (Optional[str]): the path of the source file, if known
+        """
+        reporter: FileReporter = self.reporter.for_file(path)
+        self.set_reporter(reporter)
+
         lexer: MidasLexer = MidasLexer(source)
         tokens: list[Token] = lexer.process()
         parser: MidasParser = MidasParser(tokens)
@@ -92,6 +85,14 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[Type], m.Type.Visitor[Type
         self.resolve(stmts)
 
     def type_of(self, expr: m.Expr) -> Type:
+        """Compute the type of the given expression
+
+        Args:
+            expr (m.Expr): the expression to type
+
+        Returns:
+            Type: the type of the expression
+        """
         type: Type = expr.accept(self)
         return type
 
@@ -112,6 +113,21 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[Type], m.Type.Visitor[Type
         return self.types.get_type(name)
 
     def get_variable(self, name: str) -> Type:
+        """Get the type of a variable
+
+        This function will first look into the current predicate's parameters if
+        we are in a predicate definition.
+        The the variable is looked up in the preamble (i.e. global environment)
+
+        Args:
+            name (str): the name of the variable
+
+        Raises:
+            NameError: if the variable cannot be found
+
+        Returns:
+            Type: the type of the variable
+        """
         if name in self._predicate_params:
             return self._predicate_params[name]
         predicate: Optional[Predicate] = self.types.lookup_predicate(name)
@@ -139,6 +155,11 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[Type], m.Type.Visitor[Type
                 self.types._types[name] = inferrer.infer(type)
 
     def assert_bool(self, expr: m.Expr):
+        """Check that the given expression is a subtype of `bool` or report an error
+
+        Args:
+            expr (m.Expr): the expression to check
+        """
         type: Type = self.type_of(expr)
         if not self.types.is_subtype(type, self._bool):
             self.reporter.error(expr.location, f"Must be a boolean but is {type}")
@@ -152,11 +173,18 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[Type], m.Type.Visitor[Type
         if len(params) != 0:
             type = GenericType(name=name, params=params, body=type)
         else:
-            type = AliasType(name=name, type=type)
+            type = DerivedType(name=name, type=type)
         self.types.define_type(name, type)
         self._local_variables.clear()
         self._current_name = None
 
+    def visit_alias_stmt(self, stmt: m.AliasStmt) -> None:
+        name: str = stmt.name.lexeme
+        self._current_name = name
+        type: Type = stmt.type.accept(self)
+        self.types.define_type(name, type)
+        self._current_name = None
+
     def visit_member_stmt(self, stmt: m.MemberStmt) -> None: ...
 
     def visit_extend_stmt(self, stmt: m.ExtendStmt) -> None:
@@ -183,9 +211,7 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[Type], m.Type.Visitor[Type
                 self._predicate_params[param.name.lexeme] = param.type.accept(self)
 
         type: Type = self.type_of(stmt.body)
-        params: list[TypedParamSpec] = [
-            self._visit_param_spec(spec) for spec in stmt.params
-        ]
+        params: list[ParamSpec] = [self._visit_param_spec(spec) for spec in stmt.params]
 
         if not self._is_valid_predicate(type):
             self.reporter.error(
@@ -196,9 +222,7 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[Type], m.Type.Visitor[Type
             type = self._bool
             for spec in reversed(params):
                 type = Function(
-                    pos_args=spec.pos,
-                    args=spec.mixed,
-                    kw_args=spec.kw,
+                    params=spec,
                     returns=type,
                 )
         self._predicate_params = {}
@@ -212,6 +236,16 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[Type], m.Type.Visitor[Type
         )
 
     def _is_valid_predicate(self, body: Type) -> bool:
+        """Check whether the given type is valid as a predicate's body
+
+        Accepted types are either subtypes of `bool` or valid predicates
+
+        Args:
+            body (Type): the potential predicate body
+
+        Returns:
+            bool: `True` if `body` can be a predicate body, `False` otherwise
+        """
         match body:
             case Function(returns=returns):
                 return self._is_valid_predicate(returns)
@@ -237,7 +271,11 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[Type], m.Type.Visitor[Type
         return self._visit_binary_expr(expr.location, expr.left, expr.right, method)
 
     def _visit_binary_expr(
-        self, location: Location, left_expr: m.Expr, right_expr: m.Expr, method: str
+        self,
+        location: Location,
+        left_expr: m.Expr,
+        right_expr: m.Expr,
+        method: str,
     ) -> Type:
         left: Type = self.type_of(left_expr)
         right: Type = self.type_of(right_expr)
@@ -250,15 +288,20 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[Type], m.Type.Visitor[Type
             )
             return UnknownType()
 
-        result: Optional[Type] = self._get_call_result(
-            location,
-            operation,
-            [(right_expr, right)],
-            {},
+        result: CallResult = self.dispatcher.get_result(
+            location=location,
+            callee=operation,
+            positional=[(right_expr, right)],
+            keywords={},
         )
-        return result or UnknownType()
+        return result.result
 
     def visit_unary_expr(self, expr: m.UnaryExpr) -> Type:
+        # Special case because there is no __not__ dunder method
+        match expr.operator:
+            case Token(type=TokenType.BANG):
+                return self.types.get_type("bool")
+
         method: Optional[str] = MIDAS_UNARY_METHODS.get(expr.operator.type)
         if method is None:
             self.logger.warning(f"Unsupported operator {expr.operator.lexeme}")
@@ -276,31 +319,29 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[Type], m.Type.Visitor[Type
             )
             return UnknownType()
 
-        result: Optional[Type] = self._get_call_result(
-            expr.location,
-            operation,
-            [],
-            {},
+        result: CallResult = self.dispatcher.get_result(
+            location=expr.location,
+            callee=operation,
+            positional=[],
+            keywords={},
         )
-        return result or UnknownType()
+        return result.result
 
     def visit_call_expr(self, expr: m.CallExpr) -> Type:
         callee: Type = expr.callee.accept(self)
-        positional: list[TypedExpr] = [
+        positional: list[tuple[m.Expr, Type]] = [
             (arg, self.type_of(arg)) for arg in expr.arguments
         ]
-        keywords: dict[str, TypedExpr] = {
+        keywords: dict[str, tuple[m.Expr, Type]] = {
             name: (arg, self.type_of(arg)) for name, arg in expr.keywords.items()
         }
-        return (
-            self._get_call_result(
-                expr.location,
-                callee,
-                positional,
-                keywords,
-            )
-            or UnknownType()
+        result: CallResult = self.dispatcher.get_result(
+            location=expr.location,
+            callee=callee,
+            positional=positional,
+            keywords=keywords,
         )
+        return result.result
 
     def visit_get_expr(self, expr: m.GetExpr) -> Type:
         object: Type = expr.expr.accept(self)
@@ -347,6 +388,16 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[Type], m.Type.Visitor[Type
             return UnknownType()
 
     def visit_generic_type(self, type: m.GenericType) -> Type:
+        match type.type:
+            case m.NamedType(name=Token(lexeme="Column")):
+                if len(type.args) != 1:
+                    self.reporter.error(
+                        type.location,
+                        f"Column requires 1 type argument, {len(type.args)} provided",
+                    )
+                    return ColumnType(type=UnknownType())
+                return ColumnType(type=type.args[0].accept(self))
+
         type_: Type = type.type.accept(self)
         args: list[Type] = [arg.accept(self) for arg in type.args]
         try:
@@ -375,30 +426,46 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[Type], m.Type.Visitor[Type
         )
 
     def visit_function_type(self, type: m.FunctionType) -> Type:
-        params: TypedParamSpec = self._visit_param_spec(type.params)
         return Function(
-            pos_args=params.pos,
-            args=params.mixed,
-            kw_args=params.kw,
+            params=self._visit_param_spec(type.params),
             returns=type.returns.accept(self),
         )
 
-    def _visit_param_spec(self, spec: m.ParamSpec) -> TypedParamSpec:
+    def _visit_param_spec(self, spec: m.ParamSpec) -> ParamSpec:
         n_pos: int = len(spec.pos)
         n_mixed: int = len(spec.mixed)
 
-        def process_arg(arg: m.FunctionType.Argument, i: int) -> Function.Argument:
-            return Function.Argument(
+        def process_param(
+            param: m.FunctionType.Parameter, i: int
+        ) -> Function.Parameter:
+            return Function.Parameter(
                 pos=i,
-                name=arg.name.lexeme if arg.name is not None else str(i),
-                type=arg.type.accept(self),
-                required=arg.required,
+                name=param.name.lexeme if param.name is not None else str(i),
+                type=param.type.accept(self),
+                required=param.required,
             )
 
-        return TypedParamSpec(
-            pos=[process_arg(arg, i) for i, arg in enumerate(spec.pos)],
-            mixed=[process_arg(arg, i + n_pos) for i, arg in enumerate(spec.mixed)],
-            kw=[process_arg(arg, i + n_pos + n_mixed) for i, arg in enumerate(spec.kw)],
+        return ParamSpec(
+            pos=[process_param(param, i) for i, param in enumerate(spec.pos)],
+            mixed=[
+                process_param(param, i + n_pos) for i, param in enumerate(spec.mixed)
+            ],
+            kw=[
+                process_param(param, i + n_pos + n_mixed)
+                for i, param in enumerate(spec.kw)
+            ],
+        )
+
+    def visit_frame_type(self, type: m.FrameType) -> Type:
+        def process_column(i: int, col: m.FrameType.Column) -> DataFrameType.Column:
+            return DataFrameType.Column(
+                index=i,
+                name=col.name.lexeme,
+                type=ColumnType(type=col.type.accept(self)),
+            )
+
+        return DataFrameType(
+            columns=[process_column(i, col) for i, col in enumerate(type.columns)]
         )
 
     def _resolve_type_params(self, params: list[m.TypeParam]):
@@ -412,343 +479,3 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[Type], m.Type.Visitor[Type
             self._local_variables[name] = var
             vars.append(var)
         return vars
-
-    def _get_call_result(
-        self,
-        location: Location,
-        callee: Type,
-        positional: list[TypedExpr],
-        keywords: dict[str, TypedExpr],
-        report_errors: bool = True,
-    ) -> Optional[Type]:
-        """Get the result type of a function call
-
-        If the function has overloads, the function will try to resolve the
-        appropriate signature.
-        Argument types are matched to the defined parameters.
-        The function doesn't take the raw expression as a parameter to accommodate
-        for desugared calls such as for operators.
-
-        Args:
-            location (Location): the call location
-            callee (Type): the called function
-            positional (list[TypedExpr]): the list positional arguments
-            keywords (dict[str, TypedExpr]): the map of keyword arguments
-            report_errors (bool, optional): whether type errors should be reported as diagnostics. Defaults to True.
-
-        Returns:
-            Type: the return type of the call, or `None` if either
-            the call is invalid or no overload matched the arguments uniquely
-        """
-        match callee:
-            case Function() as function:
-                valid: bool
-                mapped: list[MappedArgument]
-                valid, mapped = self.map_call_arguments(
-                    function, location, positional, keywords
-                )
-                valid = valid and self._are_arguments_valid(mapped, report_errors)
-                if not valid:
-                    return None
-                return function.returns
-
-            case OverloadedFunction(overloads=overloads):
-                function = self._match_overload(
-                    overloads, location, positional, keywords, report_errors
-                )
-                if function is None:
-                    return None
-                return function.returns
-
-            case AppliedType(body=body):
-                return self._get_call_result(
-                    location, body, positional, keywords, report_errors
-                )
-
-            case UnknownType():
-                return UnknownType()
-
-            case _:
-                if report_errors:
-                    self.reporter.error(location, f"{callee} is not callable")
-                return None
-
-    def _are_arguments_valid(
-        self,
-        arguments: list[MappedArgument],
-        report_errors: bool = True,
-    ) -> bool:
-        """Check whether the passed argument types correspond to their matched parameter definitions
-
-        Args:
-            arguments (list[MappedArgument]): the list of argument/parameter pairs
-            report_errors (bool, optional): whether type errors should be reported as diagnostics. Defaults to True.
-
-        Returns:
-            bool: True if all arguments fit the matching parameter definitions, False otherwise
-        """
-        valid: bool = True
-        for arg in arguments:
-            if not self.types.is_subtype(arg.type, arg.argument.type):
-                if report_errors:
-                    self.reporter.error(
-                        arg.expr.location,
-                        f"Wrong type for argument '{arg.argument.name}', expected {arg.argument.type}, got {arg.type}",
-                    )
-                valid = False
-        return valid
-
-    def _match_overload(
-        self,
-        overloads: list[Type],
-        location: Location,
-        positional: list[TypedExpr],
-        keywords: dict[str, TypedExpr],
-        report_errors: bool = True,
-    ) -> Optional[Function]:
-        """Try and resolve the appropriate overload for the given arguments
-
-        Args:
-            overloads (list[Type]): the list of possible overloads
-            location (Location): the call location
-            positional (list[TypedExpr]): the list of positional arguments
-            keywords (dict[str, TypedExpr]): the map of keywords arguments
-            report_errors (bool, optional): whether type errors should be reported as diagnostics. Defaults to True.
-
-        Returns:
-            Optional[Function]: the resolved function signature if it can be
-            determined unambiguously, or `None`.
-        """
-        candidates: list[OverloadCandidate] = []
-        for overload in overloads:
-            function: Type = unfold_type(overload)
-            if not isinstance(function, Function):
-                if report_errors:
-                    self.logger.error(
-                        f"Overload is not a function: {overload} is {function}"
-                    )
-                continue
-            valid, mapped = self.map_call_arguments(
-                function=function,
-                location=location,
-                positional=positional,
-                keywords=keywords,
-                report_errors=False,
-            )
-            if valid and self._are_arguments_valid(mapped, report_errors=False):
-                candidates.append(
-                    OverloadCandidate(
-                        function=function,
-                        mapped=mapped,
-                    )
-                )
-
-        pos_types: str = ", ".join(str(type) for _, type in positional)
-        kw_types: str = ", ".join(
-            f"{name}: {type}" for name, (_, type) in keywords.items()
-        )
-        for_args: str = f"for arguments pos=[{pos_types}] and kw={{{kw_types}}}"
-
-        n_candidates: int = len(candidates)
-
-        # Exactly 1 match -> return it
-        if n_candidates == 1:
-            return candidates[0].function
-
-        # No match -> invalid call
-        if n_candidates == 0:
-            overloads_str: str = ", ".join(map(str, overloads))
-            if report_errors:
-                self.reporter.error(
-                    location,
-                    f"No matching overload in [{overloads_str}] {for_args}",
-                )
-            return None
-
-        # Multiple matches -> see if one <: all others (more specific)
-        for i1, c1 in enumerate(candidates):
-            mapped1: list[MappedArgument] = c1.mapped
-            best_match: bool = True
-            for i2, c2 in enumerate(candidates):
-                if i1 == i2:
-                    continue
-                mapped2: list[MappedArgument] = c2.mapped
-                if not self._are_mapped_subtypes(mapped1, mapped2):
-                    best_match = False
-                    break
-                self.logger.debug(f"{c1.function} is a full overload of {c2.function}")
-            if best_match:
-                return c1.function
-
-        candidates_str: str = ", ".join(
-            str(candidate.function) for candidate in candidates
-        )
-        if report_errors:
-            self.reporter.error(
-                location,
-                f"Multiple matching overloads {for_args}: {candidates_str}",
-            )
-        return None
-
-    def map_call_arguments(
-        self,
-        function: Function,
-        location: Location,
-        positional: list[TypedExpr],
-        keywords: dict[str, TypedExpr],
-        report_errors: bool = True,
-    ) -> tuple[bool, list[MappedArgument]]:
-        """Map call arguments to a function's parameters as defined in its signature
-
-        This method maps positional-only, keyword-only and mixed parameter definitions
-        with the arguments passed at the call site
-
-        Any mismatched, missing or unexpected argument is reported as a diagnostic,
-        unless `report_errors` is set to `False`
-
-        Args:
-            function (Function): the function definition
-            location (Location): the call location
-            positional (list[TypedExpr]): the list of positional arguments
-            keywords (dict[str, TypedExpr]): the map of keyword arguments
-            report_errors (bool, optional): whether type errors should be reported as diagnostics. Defaults to True.
-
-        Returns:
-            tuple[bool, list[MappedArgument]]: a boolean reporting whether
-            the call is valid and the list of mapped arguments
-        """
-        set_args: set[str] = set()
-
-        required_positional: list[str] = [
-            arg.name for arg in function.pos_args + function.args if arg.required
-        ]
-        required_keyword: list[str] = [
-            arg.name for arg in function.kw_args if arg.required
-        ]
-
-        mapped: list[MappedArgument] = []
-
-        pos_params: list[Function.Argument] = list(function.pos_args)
-        mixed_params: list[Function.Argument] = list(function.args)
-        kw_params: dict[str, Function.Argument] = {
-            arg.name: arg for arg in function.kw_args
-        }
-
-        valid_call: bool = True
-
-        # TODO: handle *args and **kwargs sinks
-        for arg in positional:
-            param: Function.Argument
-            if len(pos_params) != 0:
-                param = pos_params.pop(0)
-            elif len(mixed_params) != 0:
-                param = mixed_params.pop(0)
-            else:
-                if report_errors:
-                    self.reporter.error(
-                        arg[0].location, "Too many positional arguments"
-                    )
-                valid_call = False
-                break
-            name: str = param.name
-            if name in required_positional:
-                required_positional.remove(name)
-            if name in required_keyword:
-                required_keyword.remove(name)
-            set_args.add(name)
-            mapped.append(
-                MappedArgument(
-                    expr=arg[0],
-                    type=arg[1],
-                    argument=param,
-                )
-            )
-
-        kw_params.update({arg.name: arg for arg in mixed_params})
-        for name, arg in keywords.items():
-            param: Function.Argument
-            if name not in kw_params:
-                if report_errors:
-                    if name in set_args:
-                        self.reporter.error(
-                            arg[0].location, f"Multiple values for argument '{name}'"
-                        )
-                    else:
-                        self.reporter.error(
-                            arg[0].location, f"Unknown keyword argument '{name}'"
-                        )
-                valid_call = False
-                continue
-            param = kw_params.pop(name)
-            if name in required_positional:
-                required_positional.remove(name)
-            if name in required_keyword:
-                required_keyword.remove(name)
-            set_args.add(name)
-            mapped.append(
-                MappedArgument(
-                    expr=arg[0],
-                    type=arg[1],
-                    argument=param,
-                )
-            )
-
-        def join_args(args: list[str]) -> str:
-            args = list(map(lambda a: f"'{a}'", args))
-            if len(args) == 0:
-                return ""
-            if len(args) == 1:
-                return args[0]
-            return ", ".join(args[:-1]) + " and " + args[-1]
-
-        if len(required_positional) != 0:
-            plural: str = "" if len(required_positional) == 1 else "s"
-            args: str = join_args(required_positional)
-            if report_errors:
-                self.reporter.error(
-                    location,
-                    f"Missing required positional argument{plural}: {args}",
-                )
-            valid_call = False
-
-        if len(required_keyword) != 0:
-            plural: str = "" if len(required_keyword) == 1 else "s"
-            args: str = join_args(required_keyword)
-            if report_errors:
-                self.reporter.error(
-                    location,
-                    f"Missing required keyword argument{plural}: {args}",
-                )
-            valid_call = False
-
-        return valid_call, mapped
-
-    def _are_mapped_subtypes(
-        self, mapped1: list[MappedArgument], mapped2: list[MappedArgument]
-    ) -> bool:
-        """Check whether the given argument mappings are subtype/supertype of one another
-
-        This function checks whether the argument mappings `mapped1` are subtypes
-        of `mapped2`. If any of the parameter type in `mapped1` is not a subtype
-        of the corresponding parameter in `mapped2`, `False` is returned.
-
-        This is used to check whether a given overload is
-        a more specific function/ a subtype of another.
-
-        Args:
-            mapped1 (list[MappedArgument]): the first argument mappings (subtype)
-            mapped2 (list[MappedArgument]): the second argument mappings (supertype)
-
-        Returns:
-            bool: `True` if `mapped1` is a subtype of `mapped2`, `False` otherwise
-        """
-        by_expr: dict[m.Expr, Type] = {}
-        for arg in mapped1:
-            by_expr[arg.expr] = arg.argument.type
-
-        for arg in mapped2:
-            type2: Type = arg.argument.type
-            type1: Type = by_expr[arg.expr]
-            if not self.types.is_subtype(type1, type2):
-                return False
-        return True

midas/checker/operators.py

@@ -41,7 +41,7 @@ PY_UNARY_METHODS: dict[Type[ast.unaryop], str] = {
 
 
 MIDAS_BINARY_METHODS: dict[TokenType, str] = {
-    # TokenType.PLUS: "__add__",
+    TokenType.PLUS: "__add__",
     TokenType.MINUS: "__sub__",
     TokenType.STAR: "__mul__",
     TokenType.SLASH: "__truediv__",

midas/checker/preamble.py

@@ -1,9 +1,18 @@
 from dataclasses import dataclass
-from typing import Callable, Optional
+from typing import Any, Callable, Optional
 
 from midas.checker.environment import Environment
 from midas.checker.registry import TypesRegistry
-from midas.checker.types import Function, GenericType, TopType, Type, TypeVar, UnitType
+from midas.checker.types import (
+    Function,
+    GenericType,
+    OverloadedFunction,
+    ParamSpec,
+    TopType,
+    Type,
+    TypeVar,
+    UnitType,
+)
 
 
 @dataclass(frozen=True)
@@ -14,11 +23,14 @@ class Param:
 
 
 class Preamble(Environment):
+    """The initial environment containing some of Python's builtin functions"""
+
     def __init__(self, types: TypesRegistry) -> None:
         super().__init__()
         self._types: TypesRegistry = types
-        self._python_funcs: dict[str, Callable] = {}
+        self._python_funcs: dict[str, Callable[..., Any]] = {}
 
+        self.define("__name__", self._types.get_type("str"))
         self._def_type_constructor("object", object)
         self._def_type_constructor("float", float)
         self._def_type_constructor("int", int)
@@ -34,7 +46,7 @@ class Preamble(Environment):
         # TODO: use sink
         self._def_function(
             name="print",
-            pos=[Param("object", TopType())],
+            pos=[Param("object", TopType(), required=False)],
             returns=UnitType(),
             py_function=print,
         )
@@ -64,11 +76,48 @@ class Preamble(Environment):
             pos=[Param("prompt", TopType(), required=False)],
             returns=self._types.get_type("str"),
         )
+        self._def_function(
+            name="len",
+            pos=[Param("object", TopType())],
+            returns=self._types.get_type("int"),
+        )
 
-    def _list_of(self, item_type: Type) -> Type:
-        return self._types.apply_generic(self._types.get_type("list"), [item_type])
+        T = TypeVar(name="T", bound=None)
+        self._def_overloads(
+            name="max",
+            py_function=max,
+            signatures=[
+                (
+                    [Param("arg1", T), Param("arg2", T)],
+                    [],
+                    [],
+                    T,
+                    [T],
+                ),
+                ([Param("iterable", self._list_of(T))], [], [], T, [T]),
+            ],
+        )
+        self._def_overloads(
+            name="min",
+            py_function=min,
+            signatures=[
+                (
+                    [Param("arg1", T), Param("arg2", T)],
+                    [],
+                    [],
+                    T,
+                    [T],
+                ),
+                ([Param("iterable", self._list_of(T))], [], [], T, [T]),
+            ],
+        )
 
-    def _def_type_constructor(self, name: str, py_function: Optional[Callable] = None):
+    def _list_of(self, item_type: str | Type) -> Type:
+        return self._types.list_of(item_type)
+
+    def _def_type_constructor(
+        self, name: str, py_function: Optional[Callable[..., Any]] = None
+    ):
         # TODO: more specific arg types
         self._def_function(
             name=name,
@@ -87,9 +136,9 @@ class Preamble(Environment):
         returns: Type = UnitType(),
         type_vars: list[TypeVar] = [],
     ) -> Type:
-        def map_args(params: list[Param], offset: int) -> list[Function.Argument]:
+        def map_params(params: list[Param], offset: int) -> list[Function.Parameter]:
             return [
-                Function.Argument(
+                Function.Parameter(
                     pos=i + offset,
                     name=param.name,
                     type=param.type,
@@ -99,9 +148,11 @@ class Preamble(Environment):
             ]
 
         function = Function(
-            pos_args=map_args(pos, 0),
-            args=map_args(mixed, len(pos)),
-            kw_args=map_args(kw, len(pos) + len(mixed)),
+            params=ParamSpec(
+                pos=map_params(pos, 0),
+                mixed=map_params(mixed, len(pos)),
+                kw=map_params(kw, len(pos) + len(mixed)),
+            ),
             returns=returns,
         )
         if len(type_vars) != 0:
@@ -121,7 +172,7 @@ class Preamble(Environment):
         kw: list[Param] = [],
         returns: Type = UnitType(),
         type_vars: list[TypeVar] = [],
-        py_function: Optional[Callable] = None,
+        py_function: Optional[Callable[..., Any]] = None,
     ):
         function: Type = self._make_function(
             name=name,
@@ -135,5 +186,31 @@ class Preamble(Environment):
         if py_function is not None:
             self._python_funcs[name] = py_function
 
-    def get_py_func(self, name: str) -> Optional[Callable]:
+    def _def_overloads(
+        self,
+        *,
+        name: str,
+        signatures: list[
+            tuple[list[Param], list[Param], list[Param], Type, list[TypeVar]]
+        ],
+        py_function: Optional[Callable[..., Any]] = None,
+    ):
+        overloads: list[Type] = []
+        for pos, mixed, kw, returns, type_vars in signatures:
+            overloads.append(
+                self._make_function(
+                    name=name,
+                    pos=pos,
+                    mixed=mixed,
+                    kw=kw,
+                    returns=returns,
+                    type_vars=type_vars,
+                )
+            )
+        function: Type = OverloadedFunction(overloads=overloads)
+        self.define(name, function)
+        if py_function is not None:
+            self._python_funcs[name] = py_function
+
+    def get_py_func(self, name: str) -> Optional[Callable[..., Any]]:
         return self._python_funcs.get(name)

midas/checker/registry.py

@@ -5,17 +5,20 @@ from typing import Optional
 from midas.ast.midas import MemberKind
 from midas.checker.builtins import BUILTIN_SUBTYPES
 from midas.checker.types import (
-    AliasType,
     AppliedType,
     BaseType,
+    ColumnType,
     ComplexType,
     ConstraintType,
+    DataFrameType,
+    DerivedType,
     ExtensionType,
     Function,
     GenericType,
     OverloadedFunction,
     Predicate,
     TopType,
+    TupleType,
     Type,
     TypeVar,
     UnknownType,
@@ -26,11 +29,15 @@ from midas.checker.types import (
 
 @dataclass
 class Member:
+    """A member of a type (property or method)"""
+
     kind: MemberKind
     type: Type
 
 
 class TypesRegistry:
+    """A registry of types, type members and predicates"""
+
     def __init__(self) -> None:
         self.logger: logging.Logger = logging.getLogger("TypesRegistry")
         self._types: dict[str, Type] = {}
@@ -78,6 +85,25 @@ class TypesRegistry:
         member_type: Type,
         kind: MemberKind,
     ):
+        """Define a member on a type
+
+        If the member is a method and a member with the same name is already
+        defined on the given type, the two are combined into an :class:`OverloadedFunction`.
+
+        If the member is a property and a member with the same name is already
+        defined on the given type, the new definition is dropped and an error
+        is reported.
+
+        In any case, if a member with the same name but a different kind is
+        already defined on the given type, the new definition is dropped and
+        an error is reported.
+
+        Args:
+            type_name (str): the name of the type on which the member is defined
+            member_name (str): the name of the new member
+            member_type (Type): the type of the new member
+            kind (MemberKind): the kind of member to define (property or method)
+        """
         members: dict[str, Member] = self._members.setdefault(type_name, {})
         if member_name in members:
             current: Member = members[member_name]
@@ -106,10 +132,37 @@ class TypesRegistry:
             members[member_name] = Member(kind=kind, type=member_type)
 
     def define_predicate(self, name: str, predicate: Predicate):
+        """Define a predicate
+
+        Args:
+            name (str): the name of the new predicate
+            predicate (Predicate): the predicate to define
+
+        Raises:
+            ValueError: if a predicate with the same name is already defined
+        """
         if name in self._predicates:
             raise ValueError(f"Predicate {name} already defined")
         self._predicates[name] = predicate
 
+    def is_builtin_subtype(self, name1: str, name2: str) -> bool:
+        """Check whether a type is a subtype of another base on builtin subtype rules
+
+        Args:
+            name1 (str): the name of the potential subtype
+            name2 (str): the name of the potential supertype
+
+        Returns:
+            bool: _description_
+        """
+        subtypes: set[str] = BUILTIN_SUBTYPES.get(name2, set())
+        if name1 in subtypes:
+            return True
+        for subtype in subtypes:
+            if self.is_builtin_subtype(name1, subtype):
+                return True
+        return False
+
     def is_subtype(self, type1: Type, type2: Type) -> bool:
         """Check whether `type1` is a subtype of `type2`
 
@@ -143,11 +196,11 @@ class TypesRegistry:
                     return True
                 return self.is_subtype(type1, bound)
 
-            case (AliasType(type=base1), _):
+            case (DerivedType(type=base1), _):
                 return self.is_subtype(base1, type2)
 
             case (BaseType(name=name1), BaseType(name=name2)):
-                return name1 in BUILTIN_SUBTYPES.get(name2, set())
+                return self.is_builtin_subtype(name1, name2)
 
             case (ComplexType(properties=props1), ComplexType(properties=props2)):
                 for k, t in props2.items():
@@ -157,6 +210,24 @@ class TypesRegistry:
                         return False
                 return True
 
+            case (DataFrameType(columns=columns1), DataFrameType(columns=columns2)):
+                # TODO: check order?
+                by_name1: dict[str, DataFrameType.Column] = {
+                    col.name: col for col in columns1 if col.name is not None
+                }
+                for col2 in columns2:
+                    if col2.name not in by_name1:
+                        return False
+                    if not self.is_subtype(by_name1[col2.name].type, col2.type):
+                        return False
+                return True
+
+            case (ColumnType(type=inner1), ColumnType(type=inner2)):
+                # TODO: invariant, replace ColumnType with simple GenericType
+                if not self.are_equivalent(inner1, inner2):
+                    return False
+                return True
+
             case (Function(), Function()):
                 return self.is_func_subtype(type1, type2)
 
@@ -187,6 +258,18 @@ class TypesRegistry:
 
         return False
 
+    def are_equivalent(self, type1: Type, type2: Type) -> bool:
+        """Check whether two types are equivalent (T <: S and S <: T)
+
+        Args:
+            type1 (Type): the first type
+            type2 (Type): the second type
+
+        Returns:
+            bool: whether `type1` is a subtype and a supertype of `type2`
+        """
+        return self.is_subtype(type1, type2) and self.is_subtype(type2, type1)
+
     # TODO: verify the logic in here
     def is_func_subtype(self, func1: Function, func2: Function) -> bool:
         """Check whether a function is a subtype of another
@@ -201,101 +284,121 @@ class TypesRegistry:
         if not self.is_subtype(func1.returns, func2.returns):
             return False
 
-        pos1: list[Function.Argument] = func1.pos_args
-        mixed1: list[Function.Argument] = func1.args
-        kw1: dict[str, Function.Argument] = {a.name: a for a in func1.kw_args}
-        pos2: list[Function.Argument] = func2.pos_args
-        mixed2: list[Function.Argument] = func2.args
-        kw2: dict[str, Function.Argument] = {a.name: a for a in func2.kw_args}
+        pos1: list[Function.Parameter] = func1.params.pos
+        mixed1: list[Function.Parameter] = func1.params.mixed
+        kw1: dict[str, Function.Parameter] = {
+            param.name: param for param in func1.params.kw
+        }
+        pos2: list[Function.Parameter] = func2.params.pos
+        mixed2: list[Function.Parameter] = func2.params.mixed
+        kw2: dict[str, Function.Parameter] = {
+            param.name: param for param in func2.params.kw
+        }
 
-        mixed_by_pos: dict[int, Function.Argument] = {arg.pos: arg for arg in mixed2}
-        mixed_by_name: dict[str, Function.Argument] = {arg.name: arg for arg in mixed2}
+        mixed_by_pos: dict[int, Function.Parameter] = {
+            param.pos: param for param in mixed2
+        }
+        mixed_by_name: dict[str, Function.Parameter] = {
+            param.name: param for param in mixed2
+        }
 
-        def is_arg_subtype(sub: Function.Argument, sup: Function.Argument) -> bool:
+        def is_arg_subtype(sub: Function.Parameter, sup: Function.Parameter) -> bool:
             if not self.is_subtype(sub.type, sup.type):
                 return False
             if not sup.required and sub.required:
                 return False
             return True
 
-        for arg1 in pos1:
-            arg2: Function.Argument
-            if arg1.pos < len(pos2):
-                arg2 = pos2[arg1.pos]
-            elif arg1.pos in mixed_by_pos:
-                arg2 = mixed_by_pos[arg1.pos]
-            elif not arg1.required:
+        for param1 in pos1:
+            param2: Function.Parameter
+            if param1.pos < len(pos2):
+                param2 = pos2[param1.pos]
+            elif param1.pos in mixed_by_pos:
+                param2 = mixed_by_pos[param1.pos]
+            elif not param1.required:
                 continue
             else:
                 return False
-            if not is_arg_subtype(arg2, arg1):
+            if not is_arg_subtype(param2, param1):
                 return False
 
-        for name, arg1 in kw1.items():
-            arg2: Function.Argument
+        for name, param1 in kw1.items():
+            param2: Function.Parameter
             if name in kw2:
-                arg2 = kw2[name]
+                param2 = kw2[name]
             elif name in mixed_by_name:
-                arg2 = mixed_by_name[name]
-            elif not arg1.required:
+                param2 = mixed_by_name[name]
+            elif not param1.required:
                 continue
             else:
                 return False
-            if not is_arg_subtype(arg2, arg1):
+            if not is_arg_subtype(param2, param1):
                 return False
 
-        for arg1 in mixed1:
-            pos_arg2: Optional[Function.Argument] = None
-            kw_arg2: Optional[Function.Argument] = None
-            if arg1.name in kw2:
-                kw_arg2 = kw2[arg1.name]
-            elif arg1.name in mixed_by_name:
-                kw_arg2 = mixed_by_name[arg1.name]
-            if arg1.pos < len(pos2):
-                pos_arg2 = pos2[arg1.pos]
-            elif arg1.pos in mixed_by_pos:
-                pos_arg2 = mixed_by_pos[arg1.pos]
+        for param1 in mixed1:
+            pos_param2: Optional[Function.Parameter] = None
+            kw_param2: Optional[Function.Parameter] = None
+            if param1.name in kw2:
+                kw_param2 = kw2[param1.name]
+            elif param1.name in mixed_by_name:
+                kw_param2 = mixed_by_name[param1.name]
+            if param1.pos < len(pos2):
+                pos_param2 = pos2[param1.pos]
+            elif param1.pos in mixed_by_pos:
+                pos_param2 = mixed_by_pos[param1.pos]
 
             # No match in func2 and arg is required
-            if pos_arg2 is None and kw_arg2 is None and arg1.required:
+            if pos_param2 is None and kw_param2 is None and param1.required:
                 return False
 
             # Matching keyword argument
-            if kw_arg2 is not None and not is_arg_subtype(kw_arg2, arg1):
+            if kw_param2 is not None and not is_arg_subtype(kw_param2, param1):
                 return False
 
             # Matching positional argument
-            if pos_arg2 is not None and not is_arg_subtype(pos_arg2, arg1):
+            if pos_param2 is not None and not is_arg_subtype(pos_param2, param1):
                 return False
 
-        mixed_positions: set[int] = {a.pos for a in mixed1}
-        mixed_names: set[str] = {a.name for a in mixed1}
-        for arg2 in pos2:
-            if not arg2.required:
+        mixed_positions: set[int] = {param.pos for param in mixed1}
+        mixed_names: set[str] = {param.name for param in mixed1}
+        for param2 in pos2:
+            if not param2.required:
                 continue
-            if arg2.pos >= len(pos1) and arg2.pos not in mixed_positions:
+            if param2.pos >= len(pos1) and param2.pos not in mixed_positions:
                 return False
 
-        for name, arg2 in kw2.items():
-            if not arg2.required:
+        for name, param2 in kw2.items():
+            if not param2.required:
                 continue
             if name not in kw1 and name not in mixed_names:
                 return False
 
-        for arg2 in mixed2:
-            if arg2.required:
+        for param2 in mixed2:
+            if param2.required:
                 continue
-            pos_match: bool = arg2.pos < len(pos1) or arg2.pos in mixed_positions
-            kw_match: bool = arg2.name in kw1 or arg2.name in mixed_names
+            pos_match: bool = param2.pos < len(pos1) or param2.pos in mixed_positions
+            kw_match: bool = param2.name in kw1 or param2.name in mixed_names
             if not pos_match or not kw_match:
                 return False
 
         return True
 
     def apply_generic(self, type: Type, args: list[Type]) -> Type:
+        """Instantiate a generic type with the given type arguments
+
+        Args:
+            type (Type): the generic
+            args (list[Type]): the type arguments
+
+        Raises:
+            ValueError: if the arguments are invalid (wrong number, bound violation)
+
+        Returns:
+            Type: the applied generic type
+        """
         match type:
-            case AliasType(name=name, type=base):
-                return AliasType(name=name, type=self.apply_generic(base, args))
+            case DerivedType(name=name, type=base):
+                return DerivedType(name=name, type=self.apply_generic(base, args))
 
             case GenericType(name=name, params=type_vars, body=body):
                 n_args: int = len(args)
@@ -323,6 +426,9 @@ class TypesRegistry:
                     body=substitute_typevars(body, substitutions),
                 )
 
+            case BaseType(name="tuple"):
+                return TupleType(items=tuple(args))
+
             case _:
                 raise ValueError(f"{type} is not a generic type")
 
@@ -355,6 +461,19 @@ class TypesRegistry:
         return [types[i] for i in keep]
 
     def lookup_member(self, type: Type, member_name: str) -> Optional[Type]:
+        """Lookup a member by name on a given type
+
+        This function first looks up directly on the specified type, then
+        recurse through supertypes until it finds the member or reaches
+        the root type
+
+        Args:
+            type (Type): the type on which to lookup the member
+            member_name (str): the member's name
+
+        Returns:
+            Optional[Type]: the member's type, or `None` if it is not defined
+        """
         match type:
             case BaseType(name=name):
                 if name in self._members:
@@ -362,7 +481,7 @@ class TypesRegistry:
                         return self._members[name][member_name].type
                 return None
 
-            case AliasType(name=name, type=base):
+            case DerivedType(name=name, type=base):
                 if name in self._members:
                     if member_name in self._members[name]:
                         return self._members[name][member_name].type
@@ -415,4 +534,75 @@ class TypesRegistry:
                 return None
 
     def lookup_predicate(self, name: str) -> Optional[Predicate]:
+        """Lookup a predicate by name
+
+        Args:
+            name (str): the name of the predicate
+
+        Returns:
+            Optional[Predicate]: the predicate, or `None` if is not defined
+        """
         return self._predicates.get(name)
+
+    def _by_name_or_type(self, name_or_type: str | Type) -> Type:
+        """Get a type by name or return it as is
+
+        If `name_or_type` is a string, the associated type is looked up and returned.
+        Otherwise, the type is returned as is.
+
+        Args:
+            name_or_type (str | Type): the type or type's name
+
+        Returns:
+            Type: the type
+        """
+        if isinstance(name_or_type, str):
+            return self.get_type(name_or_type)
+        return name_or_type
+
+    def list_of(self, item_type: str | Type) -> Type:
+        """Helper method to type a list of a given item type
+
+        Args:
+            item_type (str | Type): the item type
+
+        Returns:
+            Type: the list type
+        """
+        list_ = self.get_type("list")
+        return self.apply_generic(list_, [self._by_name_or_type(item_type)])
+
+    def tuple_of(self, *item_types: str | Type) -> Type:
+        """Helper method to type a tuple of given item types
+
+        Args:
+            item_type (str | Type): the item types
+
+        Returns:
+            Type: the tuple type
+        """
+
+        tuple_ = self.get_type("tuple")
+        return self.apply_generic(
+            tuple_,
+            [self._by_name_or_type(item_type) for item_type in item_types],
+        )
+
+    def dict_of(self, key_type: str | Type, value_type: str | Type) -> Type:
+        """Helper method to type a dict of given key and value types
+
+        Args:
+            key_type (str | Type): the key type
+            value_type (str | Type): the value type
+
+        Returns:
+            Type: the dict type
+        """
+        dict_ = self.get_type("dict")
+        return self.apply_generic(
+            dict_,
+            [
+                self._by_name_or_type(key_type),
+                self._by_name_or_type(value_type),
+            ],
+        )

midas/checker/reporter.py

@@ -7,6 +7,8 @@ from midas.checker.diagnostic import Diagnostic, DiagnosticType
 
 
 class Reporter:
+    """Helper class to store diagnostics"""
+
     def __init__(self):
         self.diagnostics: list[Diagnostic] = []
 
@@ -17,6 +19,14 @@ class Reporter:
         location: Location,
         message: str,
     ):
+        """Create and record a diagnostic
+
+        Args:
+            path (Optional[str]): the path linked to this diagnostic
+            type (DiagnosticType): the type of diagnostic
+            location (Location): the location if the diagnostic in the file
+            message (str): the diagnostic's message
+        """
         self.diagnostics.append(
             Diagnostic(
                 file_path=path,
@@ -27,21 +37,52 @@ class Reporter:
         )
 
     def for_file(self, path: Optional[str]) -> FileReporter:
+        """Create a new file reporter for the given path using this reporter
+
+        Args:
+            path (Optional[str]): the path for the new file reporter
+
+        Returns:
+            FileReporter: the new file reporter, linked to this reporter
+        """
         return FileReporter(self, path)
 
 
 class FileReporter:
+    """Helper class to manage diagnostics for a file"""
+
     def __init__(self, base_reporter: Reporter, path: Optional[str]) -> None:
         self.base_reporter: Reporter = base_reporter
         self.path: Optional[str] = path
 
     def for_file(self, path: Optional[str]) -> FileReporter:
+        """Create a new file reporter for the given path with the same base reporter
+
+        Args:
+            path (Optional[str]): the path for the new file reporter
+
+        Returns:
+            FileReporter: the file reporter
+        """
         return FileReporter(self.base_reporter, path)
 
     def report(self, type: DiagnosticType, location: Location, message: str):
+        """Report a diagnostic to the base reporter
+
+        Args:
+            type (DiagnosticType): the type of diagnostic
+            location (Location): the location of the diagnostic in the file
+            message (str): the diagnostic's message
+        """
         self.base_reporter.report(self.path, type, location, message)
 
     def error(self, location: Location, message: str):
+        """Report an error diagnostic
+
+        Args:
+            location (Location): the location of the diagnostic in the file
+            message (str): the diagnostic's message
+        """
         self.report(
             type=DiagnosticType.ERROR,
             location=location,
@@ -49,6 +90,12 @@ class FileReporter:
         )
 
     def warning(self, location: Location, message: str):
+        """Report a warning diagnostic
+
+        Args:
+            location (Location): the location of the diagnostic in the file
+            message (str): the diagnostic's message
+        """
         self.report(
             type=DiagnosticType.WARNING,
             location=location,
@@ -56,6 +103,12 @@ class FileReporter:
         )
 
     def info(self, location: Location, message: str):
+        """Report an info diagnostic
+
+        Args:
+            location (Location): the location of the diagnostic in the file
+            message (str): the diagnostic's message
+        """
         self.report(
             type=DiagnosticType.INFO,
             location=location,
@@ -63,6 +116,12 @@ class FileReporter:
         )
 
     def debug(self, location: Location, message: str):
+        """Report a debug diagnostic
+
+        Args:
+            location (Location): the location of the diagnostic in the file
+            message (str): the diagnostic's message
+        """
         self.report(
             type=DiagnosticType.DEBUG,
             location=location,

midas/checker/resolver.py

@@ -78,6 +78,14 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
                 return
 
     def is_defined(self, name: str) -> bool:
+        """Check whether the given variable is defined in any scope
+
+        Args:
+            name (str): the name of the variable
+
+        Returns:
+            bool: `True` if the variable is defined in a scope, `False` otherwise
+        """
         for scope in self.scopes:
             if name in scope:
                 return True
@@ -93,7 +101,11 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
             function (p.Function): the function to resolve
         """
         self.begin_scope()
-        for param in function.all_args:
+        for param in function.params.all:
+            if param.default is not None:
+                self.resolve(param.default)
+
+        for param in function.params.all:
             self.declare(param.name)
             self.define(param.name)
         self.resolve(*function.body)
@@ -128,6 +140,10 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
 
             case p.GetExpr():
                 target.accept(self)
+
+            case p.SubscriptExpr():
+                target.accept(self)
+
             case _:
                 raise Exception(f"Unsupported assignment to {target}")
 
@@ -163,6 +179,18 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
         self.resolve(*stmt.body)
         self.end_scope()
 
+    def visit_import_stmt(self, stmt: p.ImportStmt) -> None:
+        self._resolve_imports(stmt.imports)
+
+    def visit_from_import_stmt(self, stmt: p.FromImportStmt) -> None:
+        self._resolve_imports(stmt.imports)
+
+    def _resolve_imports(self, imports: list[p.ImportAlias]) -> None:
+        for import_ in imports:
+            name: str = import_.imported_name
+            self.declare(name)
+            self.define(name)
+
     def visit_raw_stmt(self, stmt: p.RawStmt) -> None:
         pass
 
@@ -232,5 +260,9 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
         if expr.step is not None:
             self.resolve(expr.step)
 
+    def visit_tuple_expr(self, expr: p.TupleExpr) -> None:
+        for item in expr.items:
+            self.resolve(item)
+
     def visit_raw_expr(self, expr: p.RawExpr) -> None:
         pass

midas/checker/types.py

@@ -2,7 +2,7 @@ from __future__ import annotations
 
 from dataclasses import dataclass, field
 from enum import StrEnum
-from typing import Optional, assert_never
+from typing import Optional, assert_never, cast
 
 import midas.ast.midas as m
 from midas.ast.printer import MidasPrinter
@@ -10,12 +10,16 @@ from midas.ast.printer import MidasPrinter
 
 @dataclass(frozen=True, kw_only=True)
 class TopType:
+    """The top type (`Any`)"""
+
     def __str__(self) -> str:
         return "Any"
 
 
 @dataclass(frozen=True, kw_only=True)
 class BaseType:
+    """A base / builtin type"""
+
     name: str
 
     def __str__(self) -> str:
@@ -23,7 +27,9 @@ class BaseType:
 
 
 @dataclass(frozen=True, kw_only=True)
-class AliasType:
+class DerivedType:
+    """A derived type, i.e. a named subtype of another type"""
+
     name: str
     type: Type
 
@@ -33,52 +39,74 @@ class AliasType:
 
 @dataclass(frozen=True, kw_only=True)
 class UnknownType:
+    """An unknown type"""
+
     def __str__(self) -> str:
         return "<Unknown>"
 
 
 @dataclass(frozen=True, kw_only=True)
 class UnitType:
+    """The unit type (`None`)"""
+
     def __str__(self) -> str:
         return "None"
 
 
 @dataclass(frozen=True, kw_only=True)
 class Function:
-    pos_args: list[Argument] = field(default_factory=list)
-    args: list[Argument] = field(default_factory=list)
-    kw_args: list[Argument] = field(default_factory=list)
+    """A function type"""
+
+    params: ParamSpec
     returns: Type
 
     def __str__(self) -> str:
-        args: list[str] = []
-        if len(self.pos_args) != 0:
-            args += list(map(str, self.pos_args))
-            args.append("/")
-
-        if len(self.args) != 0:
-            args += list(map(str, self.args))
-
-        if len(self.kw_args) != 0:
-            args.append("*")
-            args += list(map(str, self.kw_args))
-
-        return f"({', '.join(args)}) -> {self.returns}"
+        return f"{self.params} -> {self.returns}"
 
     @dataclass(frozen=True, kw_only=True)
-    class Argument:
+    class Parameter:
         pos: int
         name: str
         type: Type
         required: bool
+        unsupported: bool = False
 
         def __str__(self) -> str:
             opt: str = "" if self.required else "?"
-            return f"{self.name}: {self.type}{opt}"
+            param: str = f"{self.name}: {self.type}{opt}"
+            if self.unsupported:
+                param = f"({param})"
+            return param
+
+
+@dataclass(frozen=True, kw_only=True)
+class ParamSpec:
+    """A function's parameter spec"""
+
+    pos: list[Function.Parameter] = field(default_factory=list)
+    mixed: list[Function.Parameter] = field(default_factory=list)
+    kw: list[Function.Parameter] = field(default_factory=list)
+
+    def __str__(self) -> str:
+        params: list[str] = []
+        if len(self.pos) != 0:
+            params += list(map(str, self.pos))
+            params.append("/")
+
+        if len(self.mixed) != 0:
+            params += list(map(str, self.mixed))
+
+        if len(self.kw) != 0:
+            params.append("*")
+            params += list(map(str, self.kw))
+
+        return f"({', '.join(params)})"
 
 
 @dataclass(frozen=True, kw_only=True)
 class OverloadedFunction:
+    """A list of method overloads"""
+
     overloads: list[Type]
 
     def __str__(self) -> str:
@@ -87,6 +115,8 @@ class OverloadedFunction:
 
 @dataclass(frozen=True, kw_only=True)
 class ComplexType:
+    """A type with inline members"""
+
     members: dict[str, Type]
 
     def __str__(self) -> str:
@@ -96,6 +126,8 @@ class ComplexType:
 
 @dataclass(frozen=True, kw_only=True)
 class ExtensionType:
+    """An extension of a type, adding members through a `ComplexType`"""
+
     base: Type
     extension: ComplexType
 
@@ -104,6 +136,8 @@ class ExtensionType:
 
 
 class Variance(StrEnum):
+    """The variance of a :class:`TypeVar`"""
+
     INVARIANT = "INVARIANT"
     COVARIANT = "COVARIANT"
     CONTRAVARIANT = "CONTRAVARIANT"
@@ -111,6 +145,8 @@ class Variance(StrEnum):
 
 @dataclass(frozen=True, kw_only=True)
 class TypeVar:
+    """A type variable, often used as type parameters for a generic type"""
+
     name: str
     bound: Optional[Type]
     variance: Variance = Variance.INVARIANT
@@ -128,6 +164,8 @@ class TypeVar:
 
 @dataclass(frozen=True, kw_only=True)
 class GenericType:
+    """A generic type, with type parameters and a generic body type"""
+
     name: str
     params: list[TypeVar]
     body: Type
@@ -138,6 +176,8 @@ class GenericType:
 
 @dataclass(frozen=True, kw_only=True)
 class AppliedType:
+    """An instance of a :class:`GenericType`, with concrete type arguments substituted in its body"""
+
     name: str
     args: list[Type]
     body: Type
@@ -148,6 +188,8 @@ class AppliedType:
 
 @dataclass(frozen=True, kw_only=True)
 class ConstraintType:
+    """A type with a constraint expression"""
+
     type: Type
     constraint: m.Expr
 
@@ -156,13 +198,97 @@ class ConstraintType:
         return f"{self.type} where {printer.print(self.constraint)}"
 
 
+@dataclass(frozen=True, kw_only=True)
+class TupleType:
+    """A tuple type, containing any number of ordered item types"""
+
+    items: tuple[Type, ...]
+
+    def __str__(self) -> str:
+        return f"({', '.join(map(str, self.items))})"
+
+
+@dataclass(frozen=True, kw_only=True)
+class ColumnType:
+    """A column type containing items of a given unique type"""
+
+    type: Type
+
+    def __str__(self) -> str:
+        return f"Column[{self.type}]"
+
+
+@dataclass(frozen=True, kw_only=True)
+class DataFrameType:
+    """A data-frame type, containing named columns of specific :class:`ColumnType`"""
+
+    columns: list[Column]
+
+    def __str__(self) -> str:
+        schema: list[str] = [f"{col.name}: {col.type}" for col in self.columns]
+        return f"Frame[{', '.join(schema)}]"
+
+    @dataclass(frozen=True, kw_only=True)
+    class Column:
+        index: int
+        name: Optional[str]
+        type: ColumnType
+
+
+@dataclass(frozen=True, kw_only=True)
+class FrameGroupBy:
+    """A frame group-by object"""
+
+    frame: DataFrameType
+
+    def __str__(self) -> str:
+        return f"FrameGroupBy[{self.frame}]"
+
+
+@dataclass(frozen=True, kw_only=True)
+class ColumnGroupBy:
+    """A column group-by object"""
+
+    column: ColumnType
+
+    def __str__(self) -> str:
+        return f"ColumnGroupBy[{self.column}]"
+
+
 def substitute_typevars(type: Type, substitutions: dict[str, Type]) -> Type:
-    def sub_argument(arg: Function.Argument):
-        return Function.Argument(
-            pos=arg.pos,
-            name=arg.name,
-            type=substitute_typevars(arg.type, substitutions),
-            required=arg.required,
+    """Substitute type variables in the given type
+
+    This function is called recursively on inner type structures
+
+    Args:
+        type (Type): the type in which to substitute type variables
+        substitutions (dict[str, Type]): a mapping of type variable names to
+            concrete types
+
+    Returns:
+        Type: the resulting type with substitutions applied
+    """
+
+    def sub_parameter(param: Function.Parameter):
+        return Function.Parameter(
+            pos=param.pos,
+            name=param.name,
+            type=substitute_typevars(param.type, substitutions),
+            required=param.required,
+        )
+
+    def sub_param_spec(spec: ParamSpec):
+        return ParamSpec(
+            pos=list(map(sub_parameter, spec.pos)),
+            mixed=list(map(sub_parameter, spec.mixed)),
+            kw=list(map(sub_parameter, spec.kw)),
+        )
+
+    def sub_column(col: DataFrameType.Column):
+        return DataFrameType.Column(
+            index=col.index,
+            name=col.name,
+            type=cast(ColumnType, substitute_typevars(col.type, substitutions)),
         )
 
     match type:
@@ -175,19 +301,17 @@ def substitute_typevars(type: Type, substitutions: dict[str, Type]) -> Type:
         case BaseType():
             return type
 
-        case AliasType(name=name, type=type2):
-            return AliasType(name=name, type=substitute_typevars(type2, substitutions))
+        case DerivedType(name=name, type=type2):
+            return DerivedType(
+                name=name, type=substitute_typevars(type2, substitutions)
+            )
 
         case Function(
-            pos_args=pos_args,
-            args=args,
-            kw_args=kw_args,
+            params=params,
             returns=returns,
         ):
             return Function(
-                pos_args=list(map(sub_argument, pos_args)),
-                args=list(map(sub_argument, args)),
-                kw_args=list(map(sub_argument, kw_args)),
+                params=sub_param_spec(params),
                 returns=substitute_typevars(returns, substitutions),
             )
 
@@ -250,6 +374,31 @@ def substitute_typevars(type: Type, substitutions: dict[str, Type]) -> Type:
                 body=substitute_typevars(body, substitutions),
             )
 
+        case TupleType(items=items):
+            return TupleType(
+                items=tuple(substitute_typevars(item, substitutions) for item in items),
+            )
+
+        case ColumnType(type=items_type):
+            return ColumnType(
+                type=substitute_typevars(items_type, substitutions),
+            )
+
+        case DataFrameType(columns=columns):
+            return DataFrameType(
+                columns=list(map(sub_column, columns)),
+            )
+
+        case FrameGroupBy(frame=frame):
+            return FrameGroupBy(
+                frame=cast(DataFrameType, substitute_typevars(frame, substitutions))
+            )
+
+        case ColumnGroupBy(column=column):
+            return ColumnGroupBy(
+                column=cast(ColumnType, substitute_typevars(column, substitutions))
+            )
+
         case UnknownType() | UnitType():
             return type
 
@@ -262,22 +411,39 @@ def substitute_typevars(type: Type, substitutions: dict[str, Type]) -> Type:
 
 
 def unfold_type(type: Type) -> Type:
+    """Unfold a chain of :class:`DerivedType` to get the root supertype
+
+    Args:
+        type (Type): the type to unfold
+
+    Returns:
+        Type: the root supertype
+    """
     match type:
-        case AliasType(type=ref_type):
+        case DerivedType(type=ref_type):
             return unfold_type(ref_type)
         case _:
             return type
 
 
 def to_annotation(type: Type) -> str:
-    def _args_annotation(func: Function) -> str:
-        if len(func.kw_args) != 0:
+    """Convert the given type to a Python annotation string
+
+    Args:
+        type (Type): the type to convert
+
+    Returns:
+        str: the annotation string
+    """
+
+    def _params_annotation(spec: ParamSpec) -> str:
+        if len(spec.kw) != 0:
             return "..."
 
-        args: str = ", ".join(
-            to_annotation(arg.type) for arg in func.pos_args + func.args
+        params: str = ", ".join(
+            to_annotation(param.type) for param in spec.pos + spec.mixed
         )
-        return f"[{args}]"
+        return f"[{params}]"
 
     match type:
         case TopType():
@@ -286,7 +452,7 @@ def to_annotation(type: Type) -> str:
         case BaseType(name=name):
             return name
 
-        case AliasType(name=name):
+        case DerivedType(name=name):
             return name
 
         case UnknownType():
@@ -295,8 +461,8 @@ def to_annotation(type: Type) -> str:
         case UnitType():
             return "None"
 
-        case Function(returns=returns):
-            params_annot: str = _args_annotation(type)
+        case Function(params=params, returns=returns):
+            params_annot: str = _params_annotation(params)
             return f"Callable[{params_annot}, {to_annotation(returns)}]"
 
         case OverloadedFunction():
@@ -317,12 +483,29 @@ def to_annotation(type: Type) -> str:
         case ConstraintType():
             return str(type)
 
+        case TupleType(items=items):
+            return f"Tuple[{', '.join(map(to_annotation, items))}]"
+
+        case ColumnType():
+            return "pd.Series"
+
+        case DataFrameType():
+            return "pd.DataFrame"
+
+        case FrameGroupBy():
+            return "pd.api.typing.DataFrameGroupBy"
+
+        case ColumnGroupBy():
+            return "pd.api.typing.SeriesGroupBy"
+
         case _:
             assert_never(type)
 
 
 @dataclass(frozen=True, kw_only=True)
 class Predicate:
+    """A predicate"""
+
     type: Type
     body: m.Expr
     alias: bool
@@ -331,7 +514,7 @@ class Predicate:
 Type = (
     TopType
     | BaseType
-    | AliasType
+    | DerivedType
     | UnknownType
     | UnitType
     | Function
@@ -342,4 +525,9 @@ Type = (
     | GenericType
     | AppliedType
     | ConstraintType
+    | TupleType
+    | ColumnType
+    | DataFrameType
+    | FrameGroupBy
+    | ColumnGroupBy
 )

midas/checker/unifier.py

@@ -4,8 +4,11 @@ from typing import Optional
 from midas.checker.registry import TypesRegistry
 from midas.checker.types import (
     AppliedType,
+    ColumnType,
+    DataFrameType,
     Function,
     GenericType,
+    ParamSpec,
     TopType,
     Type,
     TypeVar,
@@ -16,6 +19,14 @@ class UnificationError(Exception): ...
 
 
 class Unifier:
+    """
+    Helper class to unify generic types in concrete usages
+
+    This can be used for example when a generic function is called with concrete
+    arguments, at which point the type parameters of the function signature
+    should be resolvable
+    """
+
     def __init__(self, types: TypesRegistry) -> None:
         self.types: TypesRegistry = types
         self.logger: logging.Logger = logging.getLogger("Unifier")
@@ -26,26 +37,37 @@ class Unifier:
         positional: list[Type],
         keywords: dict[str, Type],
     ) -> Optional[Type]:
+        """Try and unify a generic function call given concrete arguments
+
+        Args:
+            type (GenericType): the generic function type
+            positional (list[Type]): the list of positional arguments
+            keywords (dict[str, Type]): the map of keyword arguments
+
+        Returns:
+            Optional[Type]: the concrete function type if unifiable, or `None`
+        """
         concrete_func: Function = Function(
-            pos_args=[
-                Function.Argument(
-                    pos=i,
-                    name=str(i),
-                    type=arg,
-                    required=True,
-                )
-                for i, arg in enumerate(positional)
-            ],
-            args=[],
-            kw_args=[
-                Function.Argument(
-                    pos=len(positional) + i,
-                    name=name,
-                    type=arg,
-                    required=True,
-                )
-                for i, (name, arg) in enumerate(keywords.items())
-            ],
+            params=ParamSpec(
+                pos=[
+                    Function.Parameter(
+                        pos=i,
+                        name=str(i),
+                        type=arg,
+                        required=True,
+                    )
+                    for i, arg in enumerate(positional)
+                ],
+                kw=[
+                    Function.Parameter(
+                        pos=len(positional) + i,
+                        name=name,
+                        type=arg,
+                        required=True,
+                    )
+                    for i, (name, arg) in enumerate(keywords.items())
+                ],
+            ),
             returns=TopType(),  # TODO: use expected type
         )
         return self.unify_generic(type, concrete_func, match_return=False)
@@ -56,6 +78,18 @@ class Unifier:
         concrete: Type,
         match_return: bool = True,
     ) -> Optional[Type]:
+        """Unify a generic type's parameters given a concrete usage
+
+        Args:
+            template (GenericType): the generic type
+            concrete (Type): a concrete usage
+            match_return (bool, optional): if `template` is a function type,
+                whether its return type must be matched (see :func:`match`).
+                Defaults to True.
+
+        Returns:
+            Optional[Type]: the concrete type if unifiable, or `None`
+        """
         substitutions: dict[str, Type]
         try:
             substitutions = self.match(template.body, concrete, match_return)
@@ -77,6 +111,22 @@ class Unifier:
         concrete: Type,
         match_return: bool = True,
     ) -> dict[str, Type]:
+        """Match a generic type with a concrete usage, recording parameter substitutions
+
+        Args:
+            template (Type): the generic type
+            concrete (Type): a concrete usage
+            match_return (bool, optional): if `template` and `concrete` are both
+                :class:`Function`, whether their return types are also matched.
+                Defaults to True.
+
+        Raises:
+            UnificationError: if there is a conflict in parameter substitutions
+
+        Returns:
+            dict[str, Type]: the parameter substitutions which,
+                applied to `template`, yield `concrete`
+        """
         # TODO: if concrete is Generic, record bound TypeVar. Then when merging
         # substitutions, check that the constraint is respected
         match (template, concrete):
@@ -98,8 +148,32 @@ class Unifier:
 
                 return substitutions
 
+            case (
+                DataFrameType(columns=template_columns),
+                DataFrameType(columns=concrete_columns),
+            ) if len(template_columns) == len(concrete_columns):
+                substitutions: dict[str, Type] = {}
+                for template_column, concrete_column in zip(
+                    template_columns, concrete_columns
+                ):
+                    if template_column.index != concrete_column or (
+                        template_column.name != concrete_column.name
+                    ):
+                        self.logger.debug(
+                            f"Column mismatch: template={template_column}, concrete={concrete_column}"
+                        )
+                        raise UnificationError
+                    new_substistutions: dict[str, Type] = self.match(
+                        template_column.type, concrete_column.type
+                    )
+                    substitutions = self.merge(substitutions, new_substistutions)
+                return substitutions
+
+            case (ColumnType(type=template_column), ColumnType(type=concrete_column)):
+                return self.match(template_column, concrete_column)
+
             case (Function(), Function()):
-                mapped: list[tuple[Function.Argument, Function.Argument]] = (
+                mapped: list[tuple[Function.Parameter, Function.Parameter]] = (
                     self.map_params(template, concrete)
                 )
                 substitutions: dict[str, Type] = {}
@@ -122,6 +196,18 @@ class Unifier:
                 return {}
 
     def merge(self, subs1: dict[str, Type], subs2: dict[str, Type]) -> dict[str, Type]:
+        """Merge two maps of substitutions and raise an error if incompatible
+
+        Args:
+            subs1 (dict[str, Type]): the first substitutions
+            subs2 (dict[str, Type]): the second substitutions
+
+        Raises:
+            UnificationError: if there is a conflict between the two maps
+
+        Returns:
+            dict[str, Type]: the merged map of substitutions
+        """
         merged: dict[str, Type] = subs1.copy()
 
         for k, v in subs2.items():
@@ -135,19 +221,32 @@ class Unifier:
 
     def map_params(
         self, func1: Function, func2: Function
-    ) -> list[tuple[Function.Argument, Function.Argument]]:
-        pos1: list[Function.Argument] = func1.pos_args
-        mixed1: list[Function.Argument] = func1.args
-        kw1: list[Function.Argument] = func1.kw_args
+    ) -> list[tuple[Function.Parameter, Function.Parameter]]:
+        """Map parameters of two functions
 
-        pos2: list[Function.Argument] = func2.pos_args
-        mixed2: list[Function.Argument] = func2.args
-        kw2: list[Function.Argument] = func2.kw_args
+        Args:
+            func1 (Function): the first function
+            func2 (Function): the second function
 
-        mapped: list[tuple[Function.Argument, Function.Argument]] = []
+        Returns:
+            list[tuple[Function.Parameter, Function.Parameter]]: the list of parameter pairs
+        """
+        pos1: list[Function.Parameter] = func1.params.pos
+        mixed1: list[Function.Parameter] = func1.params.mixed
+        kw1: list[Function.Parameter] = func1.params.kw
 
-        by_pos2: dict[int, Function.Argument] = {arg.pos: arg for arg in pos2 + mixed2}
-        by_name2: dict[str, Function.Argument] = {arg.name: arg for arg in mixed2 + kw2}
+        pos2: list[Function.Parameter] = func2.params.pos
+        mixed2: list[Function.Parameter] = func2.params.mixed
+        kw2: list[Function.Parameter] = func2.params.kw
+
+        mapped: list[tuple[Function.Parameter, Function.Parameter]] = []
+
+        by_pos2: dict[int, Function.Parameter] = {
+            param.pos: param for param in pos2 + mixed2
+        }
+        by_name2: dict[str, Function.Parameter] = {
+            param.name: param for param in mixed2 + kw2
+        }
 
         for arg1 in pos1:
             if (arg2 := by_pos2.get(arg1.pos)) is not None:

midas/checker/variance.py

@@ -16,14 +16,27 @@ Polarity = Literal[-1, 0, 1]
 
 
 class Tracker:
+    """Helper class to track the polarity of type parameter references and computer their variance"""
+
     def __init__(self, vars: list[TypeVar]) -> None:
         self.vars: list[TypeVar] = vars
         self.refs: dict[str, set[Polarity]] = {var.name: set() for var in self.vars}
 
     def record(self, var: TypeVar, polarity: Polarity):
+        """Record a polarity of the given type parameter
+
+        Args:
+            var (TypeVar): the type parameter
+            polarity (Polarity): the polarity
+        """
         self.refs[var.name].add(polarity)
 
     def get_updated_vars(self) -> list[TypeVar]:
+        """Get a list of the tracked type variables with their recorded variance
+
+        Returns:
+            list[TypeVar]: the list of update type parameters
+        """
         return [
             TypeVar(
                 name=var.name, bound=var.bound, variance=self.get_variance(var.name)
@@ -32,6 +45,18 @@ class Tracker:
         ]
 
     def get_variance(self, name: str) -> Variance:
+        """Get the variance of a type parameter
+
+        If the type parameter is only referenced in positive positions, it is
+        covariant. If it is only referenced in negative positions, it is
+        contravariant. Otherwise, it is invariant
+
+        Args:
+            name (str): the name of the type parameter
+
+        Returns:
+            Variance: the variance of the type parameter
+        """
         refs: set[Polarity] = self.refs[name]
         if refs == {-1}:
             return Variance.CONTRAVARIANT
@@ -46,11 +71,22 @@ class Tracker:
 
 
 class VarianceInferrer:
+    """Helper class to compute type parameter variance"""
+
     def __init__(self, types: TypesRegistry) -> None:
         self.types: TypesRegistry = types
         self.tracker: Tracker = Tracker([])
 
     def infer(self, type: GenericType) -> GenericType:
+        """Infer the variance of a generic type's parameters
+
+        Args:
+            type (GenericType): the generic type
+
+        Returns:
+            GenericType: a new generic type with its parameters updated with
+                their inferred variance
+        """
         self.tracker = Tracker(type.params)
 
         self.walk(type.body, 1, type.name)
@@ -71,20 +107,36 @@ class VarianceInferrer:
         base_name: str,
         path: Optional[list[str]] = None,
     ):
+        """Walk the type nodes and record variance
+
+        This function recurses into type substructures (e.g. function parameters,
+        overloads, constraint type bases, etc.)
+
+        When recursing, the polarity is flipped for consumer positions (e.g. function
+        parameters) or kept the same for producer positions (e.g. return type)
+
+        Args:
+            type (Type): the type to visit
+            polarity (Polarity): the current polarity
+            base_name (str): the root generic type name (used to detect and
+                handle cyclic references)
+            path (Optional[list[str]], optional): the path to reach the current
+                type from the root generic type (used for debugging). Defaults to None.
+        """
         if path is None:
             path = []
 
         match type:
             # Arguments are negative positions -> flip polarity
             # Return is positive position -> keep polarity
-            case Function(pos_args=pos_args, args=mixed_args, kw_args=kw_args):
-                all_args: list[Function.Argument] = pos_args + mixed_args + kw_args
-                for arg in all_args:
+            case Function(params=spec):
+                all_params: list[Function.Parameter] = spec.pos + spec.mixed + spec.kw
+                for param in all_params:
                     self.walk(
-                        arg.type,
+                        param.type,
                         -polarity,
                         base_name,
-                        path + [f"arg:'{arg.name}'"],
+                        path + [f"param:'{param.name}'"],
                     )
 
                 self.walk(type.returns, polarity, base_name, path + ["return"])

midas/cli/commands/compile.py

@@ -5,7 +5,7 @@
 
 import sys
 from pathlib import Path
-from typing import TextIO
+from typing import Optional, TextIO
 
 import click
 
@@ -19,18 +19,23 @@ from midas.utils import TypedAST
 @click.command(help="Compile source")
 @click.argument("file", type=click.File("r"))
 @click.option("-t", "--types", type=click.File("r"), multiple=True)
+@click.option("-s", "--stubs", type=str, multiple=True)
 @click.option("--ignore-errors", is_flag=True)
 def compile(
     file: TextIO,
     types: tuple[TextIO],
+    stubs: tuple[str],
     ignore_errors: bool,
 ):
     source: str = file.read()
     source_path: Path = Path(file.name).resolve()
 
     checker = TypeChecker()
-    for types_file in types:
-        checker.import_midas(Path(types_file.name).resolve())
+    type_files: list[tuple[Path, Optional[str]]] = []
+    for i, types_file in enumerate(types):
+        in_path: Path = Path(types_file.name).resolve()
+        checker.import_midas(in_path)
+        type_files.append((in_path, stubs[i] if i < len(stubs) else None))
 
     typed_ast: TypedAST = checker.type_check_source(source, str(source_path))
     diagnostics: list[Diagnostic] = checker.diagnostics.copy()
@@ -43,4 +48,4 @@ def compile(
         sys.exit(1)
 
     generator = Generator(workdir=source_path.parent, types=checker.types)
-    generator.generate(typed_ast, source_path)
+    generator.generate(typed_ast, source_path, type_files=type_files)

midas/cli/commands/registry.py

@@ -11,14 +11,14 @@ import click
 from midas.ast.printer import MidasPrinter
 from midas.checker.checker import TypeChecker
 from midas.checker.registry import Member
-from midas.checker.types import AliasType, AppliedType, BaseType, GenericType, Type
+from midas.checker.types import AppliedType, BaseType, DerivedType, GenericType, Type
 
 
 def base_type(type: Type) -> Type:
     match type:
         case BaseType():
             return type
-        case AliasType(type=base):
+        case DerivedType(type=base):
             return base
         case AppliedType(body=body):
             return body

midas/cli/commands/stubs.py

@@ -1,7 +1,7 @@
 import ast
 import time
 from pathlib import Path
-from typing import TextIO
+from typing import Optional, TextIO
 
 import black
 import click
@@ -38,15 +38,17 @@ class Handler(FileSystemEventHandler):
 
 @click.command(help="Generate stubs from Midas definitions")
 @click.argument("file", type=click.File("r"))
-@click.option("-o", "--output", type=click.File("w"), default="-")
+@click.option("-o", "--output", type=click.File("w"))
 @click.option("-w", "--watch", is_flag=True)
 def stubs(
     file: TextIO,
-    output: TextIO,
+    output: Optional[TextIO],
     watch: bool,
 ):
     source_path: Path = Path(file.name).resolve()
-    out_path: Path = Path(output.name).resolve()
+    out_path: Path = source_path.with_suffix(".pyi")
+    if output is not None:
+        out_path = Path(output.name).resolve()
     generate_stubs(source_path, out_path)
 
     if watch:

midas/cli/highlighter.py

@@ -134,9 +134,9 @@ class PythonHighlighter(
 
     def visit_base_type(self, node: p.BaseType) -> None:
         self.wrap(node, "base-type")
-        if node.param is not None:
-            self.wrap(node.param, "param")
-            node.param.accept(self)
+        for arg in node.args:
+            self.wrap(arg, "arg")
+            arg.accept(self)
 
     def visit_constraint_type(self, node: p.ConstraintType) -> None:
         self.wrap(node, "constraint-type")
@@ -157,15 +157,18 @@ class PythonHighlighter(
 
     def visit_function(self, stmt: p.Function) -> None:
         self.wrap(stmt, "function")
-        for arg in stmt.posonlyargs + stmt.args + stmt.kwonlyargs:
-            self._highlight_function_argument(arg)
+        self._highlight_param_spec(stmt.params)
         for body_stmt in stmt.body:
             body_stmt.accept(self)
 
-    def _highlight_function_argument(self, arg: p.Function.Argument) -> None:
-        self.wrap(arg, "argument")
-        if arg.type is not None:
-            arg.type.accept(self)
+    def _highlight_param_spec(self, spec: p.ParamSpec) -> None:
+        for param in spec.all:
+            self._highlight_function_param(param)
+
+    def _highlight_function_param(self, param: p.Function.Parameter) -> None:
+        self.wrap(param, "parameter")
+        if param.type is not None:
+            param.type.accept(self)
 
     def visit_type_assign(self, stmt: p.TypeAssign) -> None:
         stmt.type.accept(self)
@@ -247,6 +250,10 @@ class PythonHighlighter(
         if expr.step is not None:
             expr.step.accept(self)
 
+    def visit_tuple_expr(self, expr: p.TupleExpr) -> None:
+        for item in expr.items:
+            item.accept(self)
+
     def visit_raw_expr(self, expr: p.RawExpr) -> None: ...
 
     def visit_raw_stmt(self, stmt: p.RawStmt) -> None: ...
@@ -350,6 +357,14 @@ class MidasHighlighter(
         for param in spec.pos + spec.mixed + spec.kw:
             param.type.accept(self)
 
+    def visit_frame_type(self, type: m.FrameType) -> None:
+        self.wrap(type, "frame")
+        for column in type.columns:
+            self._visit_frame_column(column)
+
+    def _visit_frame_column(self, column: m.FrameType.Column) -> None:
+        self.wrap(column, "column")
+
 
 class DiagnosticsHighlighter(Highlighter):
     EXTRA_CSS_PATH: Optional[Path] = Path(__file__).parent / "hl_diagnostic.css"

midas/cli/hl_diagnostic.css

@@ -4,9 +4,11 @@ span {
     &.error {
         --col: 255, 0, 0;
     }
+
     &.warning {
         --col: 250, 160, 0;
     }
+
     &.info {
         --col: 150, 190, 250;
     }
@@ -19,12 +21,12 @@ span {
         }
 
         &:hover:not(:has(.with-msg:hover)) {
-            .message {
+            &>.message {
                 display: inline-block;
             }
         }
 
-        .message {
+        &>.message {
             position: absolute;
             top: calc(100% + 0.2em);
             left: -.2em;
@@ -33,7 +35,8 @@ span {
             padding: 0.2em 0.4em;
             border-radius: .2em;
             z-index: 10;
-            width: 300%;
+            width: max-content;
+            max-width: 60vw;
         }
     }
 }

midas/cli/hl_python.css

@@ -3,7 +3,7 @@ span {
         --col: 108, 233, 108;
     }
 
-    &.param {
+    &.arg {
         --col: 103, 192, 224;
     }
 
@@ -23,7 +23,7 @@ span {
         --col: 215, 103, 224;
     }
 
-    &.argument {
+    &.parameter {
         --col: 103, 192, 224;
     }
 }

midas/cli/utils.py

@@ -68,7 +68,7 @@ class DiagnosticPrinter:
 
         loc: Location = diagnostic.location
         if loc.lineno != loc.end_lineno:
-            print(diagnostic)
+            self.print_multiline(lines, diagnostic, indent)
             return
 
         start_offset: int = loc.col_offset
@@ -95,3 +95,27 @@ class DiagnosticPrinter:
         print(indent_str + before + subject + after)
         print(indent_str + cursor)
         print()
+
+    def print_multiline(
+        self, all_lines: list[str], diagnostic: Diagnostic, indent: int = 4
+    ):
+        loc: Location = diagnostic.location
+        lines: list[str] = all_lines[loc.lineno - 1 : loc.end_lineno]
+
+        start_offset: int = loc.col_offset
+        end_offset: int = loc.end_col_offset or (start_offset + 1)
+
+        indent_str: str = " " * indent
+        color: int = self.COLORS.get(diagnostic.type, Ansi.WHITE)
+        res: str = indent_str + lines[0][:start_offset]
+        res += Ansi.FG(color) + lines[0][start_offset:]
+        for line in lines[1:-1]:
+            res += "\n" + indent_str + line
+        res += "\n" + indent_str + lines[-1][:end_offset]
+        res += Ansi.RESET + lines[-1][end_offset:]
+
+        print(diagnostic.location_str + ":")
+        print(res)
+        print()
+        print(Ansi.FG(color) + diagnostic.message + Ansi.RESET)
+        print()

midas/generator/collector.py

@@ -0,0 +1,124 @@
+import ast
+from dataclasses import dataclass
+from typing import Callable
+
+import midas.ast.python as p
+
+AssertionBuilder = Callable[..., ast.expr]
+"""A callback function which builds an assertion test given some input expressions"""
+
+
+@dataclass
+class Assertion:
+    """Runtime assertion to generate, bound to an expression"""
+
+    bound_expr: p.Expr
+    """The expression the assertion is bound to"""
+
+    inputs: list[p.Expr]
+    """
+    Expressions needed for the assertion
+    
+    Each expression will be converted by the generator and passed as individual
+    arguments to `builder`
+    """
+
+    builder: AssertionBuilder
+    """The callback to build the assertion test given converted expression from `inputs`"""
+
+    message: str
+    """The assertion message"""
+
+    def is_bound_to(self, expr: p.Expr) -> bool:
+        """Check whether this assertion is bound to the given expression
+
+        Args:
+            expr (p.Expr): the expression
+
+        Returns:
+            bool: whether this assertion is bound to `expr`
+        """
+        return expr == self.bound_expr
+
+
+class AssertionCollector:
+    """Helper class to collect assertions from outside the generator"""
+
+    def __init__(self):
+        self.assertions: list[Assertion] = []
+        self.definitions: dict[str, ast.stmt] = {}
+
+    def add(
+        self,
+        bound_expr: p.Expr,
+        inputs: list[p.Expr],
+        builder: AssertionBuilder,
+        message: str,
+    ):
+        """Add an assertion bound to the given expression
+
+        Args:
+            bound_expr (p.Expr): the expression before which the assertion
+                must be generated
+            inputs (list[p.Expr]): the list of input expressions (see :class:`Assertion`)
+            builder (AssertionBuilder): the builder callback (see :class:`Assertion`)
+            message (str): the assertion message
+        """
+        self.assertions.append(
+            Assertion(
+                bound_expr=bound_expr,
+                inputs=inputs,
+                builder=builder,
+                message=message,
+            )
+        )
+
+    def remove(self, assertion: Assertion):
+        """Remove the given assertion from the collection
+
+        Args:
+            assertion (Assertion): the assertion to remove
+        """
+        try:
+            self.assertions.remove(assertion)
+        except ValueError:
+            pass
+
+    def define(self, name: str, stmt: ast.stmt):
+        """Register a statement definition
+
+        This method will only register the first definition of any given name
+
+        Args:
+            name (str): the name of the definition
+            stmt (ast.stmt): the definition statement, like a function def
+        """
+        if name not in self.definitions:
+            self.definitions[name] = stmt
+
+    def get_definitions(self) -> list[ast.stmt]:
+        """Get the list of definitions
+
+        Returns:
+            list[ast.stmt]: the list of definitions
+        """
+        return list(self.definitions.values())
+
+    def get_assertions(self) -> list[Assertion]:
+        """Get the list of assertions
+
+        Returns:
+            list[Assertion]: the list of assertions
+        """
+        return self.assertions
+
+    def get_assertions_for(self, expr: p.Expr) -> list[Assertion]:
+        """Get the list of assertions bound to a given expression
+
+        Args:
+            expr (p.Expr): the expression
+
+        Returns:
+            list[Assertion]: the list of assertions bound to `expr`
+        """
+        return list(filter(lambda a: a.is_bound_to(expr), self.assertions))

midas/generator/constraints.py

@@ -5,6 +5,7 @@ import midas.ast.midas as m
 from midas.checker.registry import TypesRegistry
 from midas.checker.types import (
     Function,
+    ParamSpec,
     Predicate,
     Type,
     to_annotation,
@@ -17,14 +18,14 @@ LOGICAL_OPERATORS: dict[TokenType, type[ast.boolop]] = {
 }
 
 BINARY_OPERATORS: dict[TokenType, type[ast.operator]] = {
-    # TokenType.PLUS: ast.Add,
+    TokenType.PLUS: ast.Add,
     TokenType.MINUS: ast.Sub,
     TokenType.STAR: ast.Mult,
     TokenType.SLASH: ast.Div,
 }
 
 UNARY_OPERATORS: dict[TokenType, type[ast.unaryop]] = {
-    # TokenType.PLUS: ast.UAdd,
+    TokenType.PLUS: ast.UAdd,
     TokenType.MINUS: ast.USub,
 }
 
@@ -39,6 +40,8 @@ COMPARISON_OPERATORS: dict[TokenType, type[ast.cmpop]] = {
 
 
 class ConstraintGenerator(m.Expr.Visitor[ast.expr]):
+    """Class to generate Python code for constraint expressions"""
+
     def __init__(self, types: TypesRegistry):
         self.types: TypesRegistry = types
         self._id: int = 0
@@ -46,24 +49,37 @@ class ConstraintGenerator(m.Expr.Visitor[ast.expr]):
         self._aliases: dict[str, str] = {}
 
     def get_definitions(self) -> list[ast.stmt]:
+        """Get the list of definitions
+
+        Returns:
+            list[ast.stmt]: the list of definitions
+        """
         return self._definitions
 
     def generate(self, expr: m.Expr) -> ast.expr:
+        """Translate the given Midas expression to a Python expression
+
+        Args:
+            expr (m.Expr): the expression to translate
+
+        Returns:
+            ast.expr: the equivalent Python expression
+        """
         match expr:
             case m.VariableExpr():
                 return expr.accept(self)
             case _:
                 func = Function(
-                    pos_args=[],
-                    args=[
-                        Function.Argument(
-                            pos=0,
-                            name="_",
-                            type=self.types.get_type("Any"),
-                            required=True,
-                        )
-                    ],
-                    kw_args=[],
+                    params=ParamSpec(
+                        mixed=[
+                            Function.Parameter(
+                                pos=0,
+                                name="_",
+                                type=self.types.get_type("Any"),
+                                required=True,
+                            )
+                        ],
+                    ),
                     returns=self.types.get_type("bool"),
                 )
                 alias: str = self.make_alias(None)
@@ -74,6 +90,14 @@ class ConstraintGenerator(m.Expr.Visitor[ast.expr]):
                 return ast.Name(id=alias)
 
     def make_alias(self, name: Optional[str]) -> str:
+        """Get a unique alias for a predicate
+
+        Args:
+            name (Optional[str]): the name of the predicate as defined by the user
+
+        Returns:
+            str: a unique name
+        """
         suffix: str
         if name is None:
             suffix = f"p{self._id}"
@@ -84,6 +108,15 @@ class ConstraintGenerator(m.Expr.Visitor[ast.expr]):
         return alias
 
     def make_definition(self, name: str, predicate: Predicate) -> ast.stmt:
+        """Translate the given predicate to a Python definition (or assignment)
+
+        Args:
+            name (str): the name of the predicate
+            predicate (Predicate): the predicate
+
+        Returns:
+            ast.stmt: the equivalent Python statement
+        """
         body: ast.expr = predicate.body.accept(self)
         if predicate.alias:
             return ast.Assign(
@@ -94,28 +127,36 @@ class ConstraintGenerator(m.Expr.Visitor[ast.expr]):
             )
         return self.make_func(name, [ast.Return(value=body)], predicate.type)
 
-    def make_args(self, func: Function) -> ast.arguments:
+    def make_args(self, params: ParamSpec) -> ast.arguments:
+        """Translate the given parameter spec into an `ast.arguments` node
+
+        Args:
+            params (ParamSpec): the parameter spec to translate
+
+        Returns:
+            ast.arguments: the equivalent `ast.arguments`
+        """
         return ast.arguments(
             posonlyargs=[
                 ast.arg(
-                    arg=arg.name,
-                    annotation=ast.Constant(value=to_annotation(arg.type)),
+                    arg=param.name,
+                    annotation=ast.Constant(value=to_annotation(param.type)),
                 )
-                for arg in func.pos_args
+                for param in params.pos
             ],
             args=[
                 ast.arg(
-                    arg=arg.name,
-                    annotation=ast.Constant(value=to_annotation(arg.type)),
+                    arg=param.name,
+                    annotation=ast.Constant(value=to_annotation(param.type)),
                 )
-                for arg in func.args
+                for param in params.mixed
             ],
             kwonlyargs=[
                 ast.arg(
-                    arg=arg.name,
-                    annotation=ast.Constant(value=to_annotation(arg.type)),
+                    arg=param.name,
+                    annotation=ast.Constant(value=to_annotation(param.type)),
                 )
-                for arg in func.kw_args
+                for param in params.kw
             ],
             defaults=[],
             kw_defaults=[],
@@ -124,12 +165,39 @@ class ConstraintGenerator(m.Expr.Visitor[ast.expr]):
     def make_func(
         self, name: str, inner_body: list[ast.stmt], type: Type, level: int = 0
     ) -> ast.stmt:
+        """Generate a Python function def with the given name, body and signature
+
+        If `type` returns a function, the curried arguments are separated into
+        inner methods.
+        For example, if `type` is `(a: int) -> (b: int) -> (c: int) -> int`, the
+        following function would be generated:
+        ```python
+        def predicate(a: int):
+            def inner0(b: int):
+                def inner1(c: int):
+                    return ...
+                return inner1
+            return inner0
+        ```
+
+        Args:
+            name (str): the name of the outer function
+            inner_body (list[ast.stmt]): the body of the innermost function
+            type (Type): the function type / signature
+            level (int, optional): the current nesting level. Defaults to 0.
+
+        Raises:
+            ValueError: if `type` is not a function
+
+        Returns:
+            ast.stmt: the equivalent Python function definition
+        """
         match type:
-            case Function(returns=Function()):
+            case Function(params=params, returns=Function()):
                 inner_name: str = f"inner{level}"
                 return ast.FunctionDef(
                     name=name,
-                    args=self.make_args(type),
+                    args=self.make_args(params),
                     body=[
                         self.make_func(inner_name, inner_body, type.returns, level + 1),
                         ast.Return(value=ast.Name(id=inner_name)),
@@ -138,10 +206,10 @@ class ConstraintGenerator(m.Expr.Visitor[ast.expr]):
                     decorator_list=[],
                 )
 
-            case Function():
+            case Function(params=params):
                 return ast.FunctionDef(
                     name=name,
-                    args=self.make_args(type),
+                    args=self.make_args(params),
                     body=inner_body,
                     returns=ast.Constant(value=to_annotation(type.returns)),
                     decorator_list=[],
@@ -151,6 +219,18 @@ class ConstraintGenerator(m.Expr.Visitor[ast.expr]):
                 raise ValueError(f"Expected function, got {type!r}")
 
     def get_predicate(self, name: str) -> Optional[ast.expr]:
+        """Get a predicate's alias, and generate its definition if first reference
+
+        When calling this function for the first time for a given predicate,
+        a Python definition and an alias are generated. Subsequent calls only
+        return the alias, without re-generating the predicate's definition
+
+        Args:
+            name (str): the predicate's name
+
+        Returns:
+            Optional[ast.expr]: the predicate's alias, or `None` if it is not defined
+        """
         if name not in self._aliases:
             predicate: Optional[Predicate] = self.types.lookup_predicate(name)
             if predicate is None:

midas/generator/stubs.py

@@ -4,16 +4,22 @@ from typing import Optional, assert_never
 import midas.ast.midas as m
 from midas.checker.registry import Member, TypesRegistry
 from midas.checker.types import (
-    AliasType,
     AppliedType,
     BaseType,
+    ColumnGroupBy,
+    ColumnType,
     ComplexType,
     ConstraintType,
+    DataFrameType,
+    DerivedType,
     ExtensionType,
+    FrameGroupBy,
     Function,
     GenericType,
     OverloadedFunction,
+    ParamSpec,
     TopType,
+    TupleType,
     Type,
     TypeVar,
     UnitType,
@@ -26,18 +32,27 @@ Empty = ast.Constant(value=...)
 
 
 class StubsGenerator:
+    """A class to generate Python stubs for user-defined Midas types"""
+
     def __init__(self, types: TypesRegistry) -> None:
         self.types: TypesRegistry = types
         self.stubs: list[ast.stmt] = []
         self.typing_imports: set[str] = set()
+        self.import_pandas: bool = False
         self.protocol_idx: int = 0
         self.stub_idx: int = 0
         self.type_var_idx: int = 0
         self.substitutions: dict[str, dict[str, Type]] = {}
 
     def generate_stubs(self) -> ast.Module:
+        """Generate a Python module of stubs for all user-defined types
+
+        Returns:
+            ast.Module: the generated module
+        """
         self.stubs = []
         self.typing_imports = set()
+        self.import_pandas = False
         for name, type in self.types._types.items():
             # Skip builtin types, not just based on name so the user can override
             # TODO: check if added members on builtin type
@@ -53,7 +68,7 @@ class StubsGenerator:
                     continue
             self.generate_stub(name, type)
 
-        imports = [
+        imports: list[ast.stmt] = [
             ast.ImportFrom(
                 module="__future__",
                 names=[ast.alias(name="annotations")],
@@ -70,11 +85,43 @@ class StubsGenerator:
                     level=0,
                 )
             )
+        if self.import_pandas:
+            imports.append(
+                ast.Import(
+                    names=[
+                        ast.alias(
+                            name="pandas",
+                            asname="pd",
+                        )
+                    ],
+                )
+            )
         return ast.Module(body=imports + self.stubs, type_ignores=[])
 
     def generate_stub(self, name: str, type: Type):
+        """Generate a stub for the given type
+
+        Args:
+            name (str): the name of the type
+            type (Type): the type
+        """
         base_type: Type = type
 
+        # TODO: improve
+        match type:
+            case DerivedType(name=name_) | GenericType(name=name_) if name_ == name:
+                pass
+            case UnitType() if name == "None":
+                pass
+            case TopType() if name == "Any":
+                pass
+            case _:
+                alias = ast.Assign(
+                    targets=[ast.Name(id=name)], value=self.dump_type(type)
+                )
+                self.add_stub(alias)
+                return
+
         members: dict[str, Member] = self.types._members.get(name, {})
         if isinstance(base_type, (BaseType, TopType, UnitType)) and len(members) == 0:
             return
@@ -95,8 +142,19 @@ class StubsGenerator:
         self.add_stub(stub)
 
     def get_bases(self, type: Type) -> tuple[list[ast.expr], dict[str, Type]]:
+        """Get the list of class bases and type parameter substitutions for a type
+
+        Args:
+            type (Type): the type whose bases to get
+
+        Returns:
+            tuple[list[ast.expr], dict[str, Type]]: a tuple containing the list
+                of class bases (already translated to Python AST nodes), and a
+                mapping of type parameter substitutions (to replace them with
+                their generated aliases)
+        """
         match type:
-            case AliasType(type=base):
+            case DerivedType(type=base):
                 return [self.dump_type(base)], {}
 
             case GenericType(params=params, body=body):
@@ -139,6 +197,16 @@ class StubsGenerator:
     def generate_body(
         self, members: dict[str, Member], substitutions: dict[str, Type]
     ) -> list[ast.stmt]:
+        """Generate a class body given its members
+
+        Args:
+            members (dict[str, Member]): the class members
+            substitutions (dict[str, Type]): a mapping of type parameter
+                substitutions (to replace them with their generated aliases)
+
+        Returns:
+            list[ast.stmt]: the generated class body statements
+        """
         if len(members) == 0:
             return [ast.Expr(value=Empty)]
 
@@ -160,8 +228,16 @@ class StubsGenerator:
         return body
 
     def dump_type(self, type: Type) -> ast.expr:
+        """Translate a type to a Python expression
+
+        Args:
+            type (Type): the type to translate
+
+        Returns:
+            ast.expr: the generated Python expression
+        """
         match type:
-            case AliasType(name=name) | GenericType(name=name) if (
+            case DerivedType(name=name) | GenericType(name=name) if (
                 name in self.substitutions
             ):
                 type = substitute_typevars(type, self.substitutions[name])
@@ -174,7 +250,7 @@ class StubsGenerator:
             case BaseType(name=name):
                 return ast.Name(id=name)
 
-            case AliasType(name=name):
+            case DerivedType(name=name):
                 return ast.Name(id=name)
 
             case UnitType():
@@ -231,12 +307,71 @@ class StubsGenerator:
             case ConstraintType():
                 return self.dump_type(type.type)
 
+            case TupleType(items=items):
+                return ast.Subscript(
+                    value=ast.Name(id="tuple"),
+                    slice=ast.Tuple(
+                        elts=[self.dump_type(item) for item in items],
+                    ),
+                )
+
+            case ColumnType():
+                self.import_pandas = True
+                return ast.Attribute(
+                    value=ast.Name(id="pd"),
+                    attr="Series",
+                )
+
+            case DataFrameType():
+                self.import_pandas = True
+                return ast.Attribute(
+                    value=ast.Name(id="pd"),
+                    attr="DataFrame",
+                )
+
+            case FrameGroupBy():
+                self.import_pandas = True
+                return ast.Attribute(
+                    value=ast.Attribute(
+                        value=ast.Attribute(
+                            value=ast.Name(id="pd"),
+                            attr="api",
+                        ),
+                        attr="typing",
+                    ),
+                    attr="DataFrameGroupBy",
+                )
+
+            case ColumnGroupBy():
+                self.import_pandas = True
+                return ast.Attribute(
+                    value=ast.Attribute(
+                        value=ast.Attribute(
+                            value=ast.Name(id="pd"),
+                            attr="api",
+                        ),
+                        attr="typing",
+                    ),
+                    attr="SeriesGroupBy",
+                )
+
             case _:
                 assert_never(type)
 
     def dump_method(
         self, name: str, method: Type, overloaded: bool = False
     ) -> list[ast.stmt]:
+        """Generate definitions for a method
+
+        Args:
+            name (str): the method's name
+            method (Type): the method's type
+            overloaded (bool, optional): whether this method is part of an
+                overloaded method (used when called recursively). Defaults to False.
+
+        Returns:
+            list[ast.stmt]: the generated function definitions
+        """
         match method:
             case Function():
                 if overloaded:
@@ -244,7 +379,7 @@ class StubsGenerator:
                 return [
                     ast.FunctionDef(
                         name=name,
-                        args=self.dump_args(method, with_self=True),
+                        args=self.dump_params(method.params, with_self=True),
                         returns=self.dump_type(method.returns),
                         body=[ast.Expr(value=Empty)],
                         decorator_list=[ast.Name(id="overload")] if overloaded else [],
@@ -264,24 +399,43 @@ class StubsGenerator:
                     )
                 ]
 
-    def dump_args(self, func: Function, with_self: bool = False) -> ast.arguments:
+    def dump_params(self, params: ParamSpec, with_self: bool = False) -> ast.arguments:
+        """Generate an `ast.arguments` node for the given parameter spec
+
+        Args:
+            params (ParamSpec): the parameter spec to translate
+            with_self (bool, optional): whether to include a `self` parameter.
+                Defaults to False.
+
+        Returns:
+            ast.arguments: the generate Python AST node
+        """
         pos: list[ast.arg] = [
-            ast.arg(arg=f"_{arg.pos}", annotation=self.dump_type(arg.type))
-            for arg in func.pos_args
+            ast.arg(
+                arg=f"_{param.pos}",
+                annotation=self.dump_type(param.type),
+            )
+            for param in params.pos
         ]
         mixed: list[ast.arg] = [
-            ast.arg(arg=arg.name, annotation=self.dump_type(arg.type))
-            for arg in func.args
+            ast.arg(
+                arg=param.name,
+                annotation=self.dump_type(param.type),
+            )
+            for param in params.mixed
         ]
         kw: list[ast.arg] = [
-            ast.arg(arg=arg.name, annotation=self.dump_type(arg.type))
-            for arg in func.kw_args
+            ast.arg(
+                arg=param.name,
+                annotation=self.dump_type(param.type),
+            )
+            for param in params.kw
         ]
         defaults: list[ast.expr] = [
-            Empty for arg in func.pos_args + func.args if not arg.required
+            Empty for param in params.pos + params.mixed if not param.required
         ]
         kw_defaults: list[Optional[ast.expr]] = [
-            None if arg.required else Empty for arg in func.kw_args
+            None if param.required else Empty for param in params.kw
         ]
         if with_self:
             arg = ast.arg(arg="self", annotation=None)
@@ -298,6 +452,14 @@ class StubsGenerator:
         )
 
     def define_protocol(self, func: Function) -> str:
+        """Generate a :class:`Protocol` to use in a function stub
+
+        Args:
+            func (Function): the function signature to define
+
+        Returns:
+            str: the name of the generated protocol
+        """
         self.add_typing_import("Protocol")
         name: str = self.new_protocol_name()
         protocol = ast.ClassDef(
@@ -307,7 +469,7 @@ class StubsGenerator:
             body=[
                 ast.FunctionDef(
                     name="__call__",
-                    args=self.dump_args(func, with_self=True),
+                    args=self.dump_params(func.params, with_self=True),
                     returns=self.dump_type(func.returns),
                     body=[ast.Expr(value=Empty)],
                     decorator_list=[],
@@ -319,33 +481,74 @@ class StubsGenerator:
         return name
 
     def new_protocol_name(self) -> str:
+        """Get a unique protocol name
+
+        Returns:
+            str: the unique protocol name
+        """
         name: str = f"_Protocol{self.protocol_idx}"
         self.protocol_idx += 1
         return name
 
     def new_stub_name(self) -> str:
+        """Get a unique stub name
+
+        Returns:
+            str: the unique stub name
+        """
         name: str = f"_Stub_{self.stub_idx}"
         self.stub_idx += 1
         return name
 
     def new_type_var_name(self) -> str:
+        """Get a unique type variable name
+
+        Returns:
+            str: the unique type variable name
+        """
         name: str = f"_T{self.type_var_idx}"
         self.type_var_idx += 1
         return name
 
     def add_stub(self, stub: ast.stmt):
+        """Append the given statement to the output
+
+        Args:
+            stub (ast.stmt): the statement to append
+        """
         self.stubs.append(stub)
 
     def add_typing_import(self, name: str):
+        """Add the given name to the list of names to import from `typing`
+
+        Args:
+            name (str): the name to import
+        """
         self.typing_imports.add(name)
 
     def define_type_vars(self, vars: list[TypeVar]) -> list[TypeVar]:
+        """Define aliases for the given type variables
+
+        Args:
+            vars (list[TypeVar]): the variables to define
+
+        Returns:
+            list[TypeVar]: new type variables named with the generated aliases
+        """
         vars2: list[TypeVar] = []
         for var in vars:
             vars2.append(self.define_type_var(var))
         return vars2
 
     def define_type_var(self, var: TypeVar) -> TypeVar:
+        """Define a type variable alias
+
+        Args:
+            var (TypeVar): the type variable to define
+
+        Returns:
+            TypeVar: a new type variable named with a uniquely generated alias
+        """
         name: str = self.new_type_var_name()
         self.add_typing_import("TypeVar")
 

midas/lexer/base.py

@@ -16,9 +16,10 @@ class Lexer(ABC):
     """An abstract lexer which provides methods to easily extend it into a concrete one
 
     This implementation is based on the [_Crafting Interpreters_][1] book by Robert Nystrom,
-    more specifically on my [previous Python implementation](https://git.kb28.ch/HEL/pebble)
+    more specifically on my [previous Python implementation][2]
 
     [1]: https://craftinginterpreters.com/
+    [2]: https://git.kb28.ch/HEL/pebble
     """
 
     def __init__(self, source: str, file: Optional[str] = None) -> None:
@@ -168,6 +169,6 @@ class Lexer(ABC):
     def scan_token(self) -> None:
         """Scan a token
 
-        This function should (at least) consume the current character and produce the appropriate token(s), using `add_token`
+        This function should (at least) consume the current character and produce the appropriate token(s), using :func:`add_token`
         """
         pass

midas/lexer/midas.py

@@ -32,6 +32,8 @@ class MidasLexer(Lexer):
                 )
             case "!" if self.match("="):
                 self.add_token(TokenType.BANG_EQUAL)
+            case "!":
+                self.add_token(TokenType.BANG)
             case ":":
                 self.add_token(TokenType.COLON)
             case ".":
@@ -46,8 +48,8 @@ class MidasLexer(Lexer):
                 self.add_token(TokenType.UNDERSCORE)
             case "-" if self.match(">"):
                 self.add_token(TokenType.ARROW)
-            # case "+":
-            #     self.add_token(TokenType.PLUS)
+            case "+":
+                self.add_token(TokenType.PLUS)
             case "-":
                 self.add_token(TokenType.MINUS)
             case "*":
@@ -81,6 +83,12 @@ class MidasLexer(Lexer):
         return None
 
     def scan_string(self, opening: str):
+        """Scan the rest of a string and add it as a token
+
+        Args:
+            opening (str): the opening quote or double quote, to be matched
+                at the end of the string
+        """
         while self.peek() != opening and not self.is_at_end():
             self.advance()
 
@@ -100,12 +108,15 @@ class MidasLexer(Lexer):
         while self.peek().isdigit():
             self.advance()
 
+        is_float: bool = False
         if self.peek() == "." and self.peek_next().isdigit():
+            is_float = True
             self.advance()
             while self.peek().isdigit():
                 self.advance()
 
-        value: float = float(self.source[self.start : self.idx])
+        value_str: str = self.source[self.start : self.idx]
+        value: int | float = float(value_str) if is_float else int(value_str)
         self.add_token(TokenType.NUMBER, value)
 
     def scan_identifier(self):
@@ -147,6 +158,18 @@ class MidasLexer(Lexer):
         self.add_token(TokenType.COMMENT)
 
     def is_identifier_char(self, char: str, *, start: bool) -> bool:
+        """Check whether a character is a valid as part of an identifier
+
+        Identifiers can contain any alphanumerical character or underscore.
+        They cannot start with a digit.
+
+        Args:
+            char (str): the character to check
+            start (bool): whether this is the first character of the identifier
+
+        Returns:
+            bool: `True` if the character is valid, `False` otherwise
+        """
         if char == "_":
             return True
         if char.isalpha():

midas/lexer/token.py

@@ -25,7 +25,7 @@ class TokenType(Enum):
     DOT = auto()
 
     # Operators
-    # PLUS = auto()
+    PLUS = auto()
     MINUS = auto()
     STAR = auto()
     SLASH = auto()
@@ -36,6 +36,7 @@ class TokenType(Enum):
     EQUAL = auto()
     EQUAL_EQUAL = auto()
     BANG_EQUAL = auto()
+    BANG = auto()
 
     # Literals
     IDENTIFIER = auto()
@@ -47,6 +48,7 @@ class TokenType(Enum):
 
     # Keywords
     TYPE = auto()
+    ALIAS = auto()
     PREDICATE = auto()
     EXTEND = auto()
     WHERE = auto()
@@ -63,6 +65,7 @@ class TokenType(Enum):
 
 KEYWORDS: dict[str, TokenType] = {
     "type": TokenType.TYPE,
+    "alias": TokenType.ALIAS,
     "predicate": TokenType.PREDICATE,
     "extend": TokenType.EXTEND,
     "where": TokenType.WHERE,
@@ -102,6 +105,15 @@ class Token:
         )
 
     def location_to(self, to: Token) -> Location:
+        """Create a new :class:`Location` spanning from this token to another
+
+        Args:
+            to (Token): the end token
+
+        Returns:
+            Location: a new :class:`Location` starting at this token and ending
+                at `to`, both included
+        """
         return Location.span(self.get_location(), to.get_location())
 
     @property

midas/parser/base.py

@@ -16,6 +16,9 @@ class TokenError:
     def get_report(self) -> str:
         """Get a detailed error message
 
+        The error message is formatted as "(<position>) Error at <token>: <message>".
+        For example: "(L2:5) Error at '3': Expected ')' after arguments."
+
         Returns:
             str: the complete error message
         """
@@ -32,9 +35,10 @@ class Parser(ABC, Generic[T]):
     """An abstract parser which provides methods to easily extend it into a concrete one
 
     This implementation is based on the [_Crafting Interpreters_][1] book by Robert Nystrom,
-    more specifically on my [previous Python implementation](https://git.kb28.ch/HEL/pebble)
+    more specifically on my [previous Python implementation][2]
 
     [1]: https://craftinginterpreters.com/
+    [2]: https://git.kb28.ch/HEL/pebble
     """
 
     IGNORE: set[TokenType] = {
@@ -173,7 +177,7 @@ class Parser(ABC, Generic[T]):
             error_msg (str): the error message if the token doesn't match
 
         Raises:
-            SyntaxError: if the current token doesn't match the given type
+            ParsingError: if the current token doesn't match the given type
 
         Returns:
             Token: the current token which matched the given type

midas/parser/midas.py

@@ -2,6 +2,7 @@ from typing import Optional
 
 from midas.ast.location import Location
 from midas.ast.midas import (
+    AliasStmt,
     BinaryExpr,
     CallExpr,
     ComplexType,
@@ -9,6 +10,7 @@ from midas.ast.midas import (
     Expr,
     ExtendStmt,
     ExtensionType,
+    FrameType,
     FunctionType,
     GenericType,
     GetExpr,
@@ -33,10 +35,11 @@ from midas.parser.base import Parser
 from midas.parser.errors import ParsingError
 
 
-class MidasParser(Parser):
+class MidasParser(Parser[list[Stmt]]):
     """A simple parser for midas type definitions"""
 
     SYNC_BOUNDARY: set[TokenType] = {
+        TokenType.ALIAS,
         TokenType.TYPE,
         TokenType.EXTEND,
         TokenType.PREDICATE,
@@ -71,14 +74,16 @@ class MidasParser(Parser):
     def declaration(self) -> Optional[Stmt]:
         """Try and parse a declaration
 
-        Any parsing error is caught and None is returned
+        Any parsing error is caught and `None` is returned
 
         Returns:
-            Optional[Stmt]: the parsed Midas statement, or None if a ParsingError was raised
+            Optional[Stmt]: the parsed Midas statement, or `None` if a ParsingError was raised
         """
         try:
             if self.match(TokenType.TYPE):
                 return self.type_declaration()
+            if self.match(TokenType.ALIAS):
+                return self.alias_declaration()
             if self.match(TokenType.EXTEND):
                 return self.extend_declaration()
             if self.match(TokenType.PREDICATE):
@@ -91,23 +96,14 @@ class MidasParser(Parser):
     def type_declaration(self) -> TypeStmt:
         """Parse a type declaration
 
-        A type declaration can either be a simple type alias or a new complex type.
-        In either case, it can have an optional template expression after its name, wrapped in brackets.
-        A simple type alias is derived from a base type expression, and can have a optional constraint expression preceded by the `where` keyword.
-        A full simple type alias is thus written:
-        ```
-        type Name[Template](TypeExpr) where Condition
-        ```
+        A type declaration creates a named subtype of a type expression.
+        It can have an optional template expression after its name, wrapped in brackets, to handle type parameters.
 
-        A new complex type has a set of properties which are named, have a type and an optional constraint expression (also preceded by the `where` keyword).
-        A full complex type definition is thus written:
-        ```
-        type Name[Template] {
-            prop1: TypeExpr1 where Condition1
-            prop2: TypeExpr2 where Condition2
-            ...
-        }
-        ```
+        A type statement consists of:
+        - the `type` keyword
+        - a name (identifier)
+        - (optional) type parameters
+        - a body, a type expression (see :func:`type_expr`)
 
         Returns:
             TypeStmt: the parsed type declaration statement
@@ -158,11 +154,35 @@ class MidasParser(Parser):
         self.consume(TokenType.RIGHT_BRACKET, "Missing ']' after type parameters")
         return params
 
+    def alias_declaration(self) -> AliasStmt:
+        """Parse an alias declaration
+
+        An alias statement consists of:
+        - the `alias` keyword
+        - a name (identifier)
+        - a body, a type expression (see :func:`type_expr`)
+
+        Returns:
+            AliasStmt: the parsed alias declaration statement
+        """
+        keyword: Token = self.previous()
+        name: Token = self.consume_identifier("Expected alias name")
+
+        self.consume(TokenType.EQUAL, "Expected '=' before alias definition")
+
+        type: Type = self.type_expr()
+
+        return AliasStmt(
+            location=keyword.location_to(self.previous()),
+            name=name,
+            type=type,
+        )
+
     def type_expr(self) -> Type:
         """Parse a type expression
 
-        A type is an identifier, optionally followed by a template expression.
-        It can also optionally be followed by a '?' to indicate a nullable type
+        A type expression can either be a function type (see :func:`function`)
+        or a constraint type (see :func:`constraint_type`)
 
         Returns:
             TypeExpr: the parsed type expression
@@ -182,6 +202,15 @@ class MidasParser(Parser):
         return base
 
     def constraint_type(self) -> Type:
+        """Parse a constraint type expression
+
+        A constraint type consists of a base type (see :func:`base_type`),
+        optionally followed by the `where` keyword and a constraint
+        expression (see :func:`constraint`)
+
+        Returns:
+            Type: the parsed constraint type expression
+        """
         type: Type = self.base_type()
         if self.match(TokenType.WHERE):
             constraint: Expr = self.constraint()
@@ -193,6 +222,14 @@ class MidasParser(Parser):
         return type
 
     def base_type(self) -> Type:
+        """Parse a base type expression
+
+        A base type is either a parenthesized type expression (see :func:`type_expr`)
+        or a generic type (see :func:`generic_type`)
+
+        Returns:
+            Type: the parsed base type expression
+        """
         if self.match(TokenType.LEFT_PAREN):
             type: Type = self.type_expr()
             self.consume(TokenType.RIGHT_PAREN, "Unclosed parenthesis")
@@ -204,8 +241,21 @@ class MidasParser(Parser):
         return self.generic_type()
 
     def generic_type(self) -> Type:
-        type: Type = self.named_type()
+        """Parse a generic type expression
+
+        A generic type consists of a named type (see :func:`named_type`),
+        optionally followed by type arguments in brackets.
+
+        The special `Frame` type accepts a frame schema instead of type
+        arguments (see :func:`frame_type`).
+
+        Returns:
+            Type: the parsed generic type
+        """
+        type: NamedType = self.named_type()
         if self.check(TokenType.LEFT_BRACKET):
+            if type.name.lexeme == "Frame":
+                return self.frame_type()
             args: list[Type] = self.type_args()
             return GenericType(
                 location=Location.span(type.location, self.previous().get_location()),
@@ -215,6 +265,13 @@ class MidasParser(Parser):
         return type
 
     def type_args(self) -> list[Type]:
+        """Parse a list of type arguments
+
+        Type arguments are a comma-separated list of type expression wrapped in brackets.
+
+        Returns:
+            list[Type]: the list of type arguments, if any, or an empty list
+        """
         args: list[Type] = []
         self.consume(TokenType.LEFT_BRACKET, "Missing '[' before generic arguments")
         while not self.is_at_end() and not self.check(TokenType.RIGHT_BRACKET):
@@ -224,7 +281,14 @@ class MidasParser(Parser):
         self.consume(TokenType.RIGHT_BRACKET, "Missing ']' after generic arguments")
         return args
 
-    def named_type(self) -> Type:
+    def named_type(self) -> NamedType:
+        """Parse a named type expression
+
+        A named type is an identifier token
+
+        Returns:
+            NamedType: the parsed named type expression
+        """
         name: Token = self.consume_identifier("Expected type name")
         return NamedType(
             location=name.get_location(),
@@ -232,13 +296,13 @@ class MidasParser(Parser):
         )
 
     def complex_type(self) -> ComplexType:
-        """Parse a type definition body
+        """Parse a complex type expression
 
-        A type definition body is a set of whitespace-separated
-        property statements enclosed in curly braces
+        A complex type consists of zero or more member statements enclosed in
+        curly braces
 
         Returns:
-            ComplexType: the parsed complex type
+            ComplexType: the parsed complex type expression
         """
         left: Token = self.consume(
             TokenType.LEFT_BRACE, "Expected '{' to start type body"
@@ -259,10 +323,50 @@ class MidasParser(Parser):
             members=members,
         )
 
-    def constraint(self) -> Expr:
-        """Parse a constraint
+    def frame_type(self) -> FrameType:
+        """Parse a frame type expression
 
-        A constraint is basically a logical predicate
+        A frame type consists of:
+        - the `Frame` identifier
+        - an opening bracket `[`
+        - a list of comma-separated column expression consisting of:
+            - a name (token)
+            - a colon `:`
+            - a type expression (see :func:`type_expr`)
+        - a closing bracket `]`
+
+        Returns:
+            FrameType: the parsed frame type
+        """
+        keyword: Token = self.previous()
+        self.consume(TokenType.LEFT_BRACKET, "Expected '[' to start frame schema")
+
+        columns: list[FrameType.Column] = []
+        while not self.check(TokenType.RIGHT_BRACKET) and not self.is_at_end():
+            name: Token = self.advance()
+            self.consume(TokenType.COLON, "Expected ':' between column name and type")
+            type: Type = self.type_expr()
+            columns.append(
+                FrameType.Column(
+                    location=name.location_to(self.previous()),
+                    name=name,
+                    type=type,
+                )
+            )
+            if not self.match(TokenType.COMMA):
+                break
+
+        self.consume(TokenType.RIGHT_BRACKET, "Unclosed frame schema")
+
+        return FrameType(
+            location=keyword.location_to(self.previous()),
+            columns=columns,
+        )
+
+    def constraint(self) -> Expr:
+        """Parse a constraint expression
+
+        A constraint is an expression (see :func:`expression`)
 
         Returns:
             Expr: the parsed constraint expression
@@ -270,10 +374,20 @@ class MidasParser(Parser):
         return self.expression()
 
     def expression(self) -> Expr:
+        """Parse an expression
+
+        An expression consists of a logical AND expression (see :func:`and_`)
+
+        Returns:
+            Expr: the parsed expression
+        """
         return self.and_()
 
     def and_(self) -> Expr:
-        """Parse a logical AND expression or a simpler expression
+        """Parse a logical AND expression
+
+        An AND consists of one or more equality expressions (see :func:`equality`)
+        separated by logical AND operators (`&`)
 
         Returns:
             Expr: the parsed expression
@@ -289,7 +403,10 @@ class MidasParser(Parser):
         return expr
 
     def equality(self) -> Expr:
-        """Parse a logical equality expression or a simpler expression
+        """Parse an equality expression
+
+        An equality consists of one or more comparison expressions (see :func:`comparison`)
+        separated by equality operators (`==`, `!=`)
 
         Returns:
             Expr: the parsed expression
@@ -305,18 +422,59 @@ class MidasParser(Parser):
         return expr
 
     def comparison(self) -> Expr:
-        """Parse a logical comparison expression or a simpler expression
+        """Parse a comparison expression
+
+        A comparison consists of one or more term expressions (see :func:`term`)
+        separated by comparison operators (`<`, `<=`, `>`, `>=`)
 
         Returns:
             Expr: the parsed expression
         """
-        expr: Expr = self.unary()
+        expr: Expr = self.term()
         while self.match(
             TokenType.LESS,
             TokenType.LESS_EQUAL,
             TokenType.GREATER,
             TokenType.GREATER_EQUAL,
         ):
+            operator: Token = self.previous()
+            right: Expr = self.term()
+            location: Location = Location.span(expr.location, right.location)
+            expr = BinaryExpr(
+                location=location, left=expr, operator=operator, right=right
+            )
+        return expr
+
+    def term(self) -> Expr:
+        """Parse a term expression
+
+        A term consists of one or more factor expressions (see :func:`factor`)
+        separated by weak arithmetic operators (`+`, `-`)
+
+        Returns:
+            Expr: the parsed expression
+        """
+        expr: Expr = self.factor()
+        while self.match(TokenType.PLUS, TokenType.MINUS):
+            operator: Token = self.previous()
+            right: Expr = self.factor()
+            location: Location = Location.span(expr.location, right.location)
+            expr = BinaryExpr(
+                location=location, left=expr, operator=operator, right=right
+            )
+        return expr
+
+    def factor(self) -> Expr:
+        """Parse a factor expression
+
+        A factor consists of one or more unary expressions (see :func:`unary`)
+        separated by strong arithmetic operators (`*`, `/`)
+
+        Returns:
+            Expr: the parsed expression
+        """
+        expr: Expr = self.unary()
+        while self.match(TokenType.STAR, TokenType.SLASH):
             operator: Token = self.previous()
             right: Expr = self.unary()
             location: Location = Location.span(expr.location, right.location)
@@ -326,12 +484,15 @@ class MidasParser(Parser):
         return expr
 
     def unary(self) -> Expr:
-        """Parse a unary expression or a simpler expression
+        """Parse a unary expression
+
+        A unary consists of a call expression (see :func:`call`) optionally
+        preceded by zero or more unary operators (`+`, `-`, `!`)
 
         Returns:
             Expr: the parsed expression
         """
-        if self.match(TokenType.MINUS):
+        if self.match(TokenType.PLUS, TokenType.MINUS, TokenType.BANG):
             operator: Token = self.previous()
             right: Expr = self.unary()
             location: Location = Location.span(operator.get_location(), right.location)
@@ -339,16 +500,48 @@ class MidasParser(Parser):
         return self.call()
 
     def call(self) -> Expr:
+        """Parse a call expression
+
+        A call consists of a reference expression (see :func:`reference`)
+        optionally followed by zero or more argument groups.
+
+        Argument groups are parenthesize, comma-separated list of arguments (see :func:`finish_call`)
+
+        Returns:
+            Expr: the parsed expression
+        """
         expr: Expr = self.reference()
         while self.match(TokenType.LEFT_PAREN):
             expr = self.finish_call(expr)
         return expr
 
     def finish_call(self, callee: Expr) -> Expr:
+        """Parse an argument group, i.e. the arguments of a call
+
+        Arguments are either passed positionally or by name (keyword argument).
+        All positional arguments must come before any keyword argument and
+        vice-versa. Arguments are separated by commas.
+
+        A positional argument simply consists of an expression (see :func:`expression`)
+
+        A keyword argument consists of and identifier, followed by the equal `=`
+        token and an expression (see :func:`expression`).
+
+        Args:
+            callee (Expr): the callee expression
+
+        Raises:
+            ParsingError: if a positional argument is passed after a keyword
+                argument or if a keyword argument's name is invalid (i.e. not
+                an identifier)
+
+        Returns:
+            Expr: the parsed call expression
+        """
         pos_args: list[Expr] = []
         kw_args: dict[str, Expr] = {}
         keywords: bool = False
-        while not self.match(TokenType.RIGHT_PAREN):
+        while not self.check(TokenType.RIGHT_PAREN):
             if self.check_identifier() and self.check_next(TokenType.EQUAL):
                 keywords = True
                 keyword: Token = self.advance()
@@ -364,13 +557,14 @@ class MidasParser(Parser):
             else:
                 value = self.expression()
                 if self.check(TokenType.EQUAL):
+                    error_msg: str
                     if keywords:
-                        raise self.error(self.peek(), "Invalid keyword argument name")
+                        error_msg = "Invalid keyword argument name"
                     else:
-                        raise self.error(
-                            self.peek(),
-                            "Cannot pass positional arguments after a keyword argument",
+                        error_msg = (
+                            "Cannot pass positional arguments after a keyword argument"
                         )
+                    raise self.error(self.peek(), error_msg)
                 pos_args.append(value)
 
             if not self.match(TokenType.COMMA):
@@ -387,7 +581,12 @@ class MidasParser(Parser):
         )
 
     def reference(self) -> Expr:
-        """Parse an attribute access expression or a simpler expression
+        """Parse a reference expression
+
+        A reference consists of a primary expression (see :func:`primary`)
+        optionally followed by zero or more attribute accesses.
+
+        An attribute access consists of a dot `.` token followed by an identifier
 
         Returns:
             Expr: the parsed expression
@@ -402,7 +601,12 @@ class MidasParser(Parser):
     def primary(self) -> Expr:
         """Parse a primary expression
 
-        This includes literals (booleans, numbers, etc.), wildcards, identifiers and grouped expressions
+        This includes literals (booleans, numbers, etc.), wildcards, identifiers
+        and grouped expressions
+
+        Raises:
+            ParsingError: if a primary expressions cannot be parsed from the
+                following tokens
 
         Returns:
             Expr: the parsed expression
@@ -435,14 +639,41 @@ class MidasParser(Parser):
         raise self.error(self.peek(), "Expected expression")
 
     def consume_identifier(self, message: str = "Expected identifier") -> Token:
+        """Consume the current token if it is a valid identifier or raise an error (see :func:`check_identifier`)
+
+        If the current token is not a valid identifier, an error is raised
+        with the provided message
+
+        Args:
+            message (str, optional): the error message. Defaults to "Expected identifier".
+
+        Raises:
+            ParsingError: if the current token is not a valid identifier
+
+        Returns:
+            Token: the current token which is a valid identifier
+        """
         if not self.match_identifier():
             raise self.error(self.peek(), message)
         return self.previous()
 
     def match_identifier(self) -> bool:
+        """Consume the next token if it is a valid identifier (see :func:`check_identifier`)
+
+        Returns:
+            bool: whether a token was matched and consumed
+        """
         return self.match(TokenType.IDENTIFIER, *KEYWORDS.values())
 
     def check_identifier(self) -> bool:
+        """Check whether the current token is a valid identifier
+
+        A valid identifier is either an identifier token or a keyword token.
+        This function always returns False if the parser is at the EOF token
+
+        Returns:
+            bool: True if the current token is a valid identifier and not EOF
+        """
         for tt in [TokenType.IDENTIFIER, *KEYWORDS.values()]:
             if self.check(tt):
                 return True
@@ -451,7 +682,14 @@ class MidasParser(Parser):
     def member_stmt(self) -> MemberStmt:
         """Parse a member statement
 
-        A type member statement is written `prop name: Type` or `def name: Type`
+        A member statement is written consists of:
+        - the `prop` (for a property) or `def` (for a method) keyword
+        - an name (identifier)
+        - a colon `:`
+        - a type expression (see :func:`type_expr`)
+
+        Raises:
+            ParsingError: if the first token is neither `prop` nor `def`
 
         Returns:
             MemberStmt: the parsed member statement
@@ -478,7 +716,13 @@ class MidasParser(Parser):
     def extend_declaration(self) -> ExtendStmt:
         """Parse an extension definition
 
-        An extension is written `extend Type { operations }` or `extend[S <: T, U] Type { operations }`
+        An extension statement consists of:
+        - the `extend` keyword
+        - a type name (identifier)
+        - (optional) type parameters (see :func:`type_params`)
+        - an opening brace `{`
+        - zero or more member statements (see :func:`member_stmt`)
+        - a closing brace `}`
 
         Returns:
             ExtendStmt: the parsed extension statement
@@ -503,7 +747,12 @@ class MidasParser(Parser):
     def predicate_declaration(self) -> PredicateStmt:
         """Parse a predicate declaration
 
-        A predicate is written `predicate Name(subject: Type) = constraint_expression`
+        A predicate statement consists of:
+        - the `predicate` keyword
+        - a name (identifier)
+        - (optional) zero or more parameter specs (see :func:`function_params`)
+        - an equal sign `=`
+        - a body, a constraint expression (see :func:`constraint`)
 
         Returns:
             PredicateStmt: the parsed predicate declaration statement
@@ -514,7 +763,7 @@ class MidasParser(Parser):
 
         params: list[ParamSpec] = []
         while self.check(TokenType.LEFT_PAREN):
-            params.append(self.function_args())
+            params.append(self.function_params())
 
         self.consume(TokenType.EQUAL, "Expected '=' after predicate subject")
         body: Expr = self.constraint()
@@ -526,7 +775,18 @@ class MidasParser(Parser):
         )
 
     def function(self) -> FunctionType:
-        params: ParamSpec = self.function_args()
+        """Parse a function type expression
+
+        A function consists of:
+        - the `fn` keyword
+        - a parameter spec (see :func:`function_params`)
+        - the arrow keyword `->`
+        - a result type expression (see :func:`type_expr`)
+
+        Returns:
+            FunctionType: the parsed function type expression
+        """
+        params: ParamSpec = self.function_params()
 
         self.consume(TokenType.ARROW, "Expected '->' before result type")
         result: Type = self.type_expr()
@@ -537,36 +797,53 @@ class MidasParser(Parser):
             returns=result,
         )
 
-    def function_args(self) -> ParamSpec:
+    def function_params(self) -> ParamSpec:
+        """Parse a parameter spec
+
+        A parameter spec consists of zero or more comma-separated parameters,
+        wrapped in parentheses.
+
+        Like in Python, it can contain positional-only, mixed and keyword-only
+        parameters (separated by `/` and `*`).
+
+        Each parameter has a type (see :func:`type_expr`),
+        preceded by a name (identifier) and a colon `:` (not required for
+        positional-only parameters).
+
+        Returns:
+            ParamSpec: the parsed parameter spec
+        """
         l_paren: Token = self.consume(
             TokenType.LEFT_PAREN, "Expected '(' before function parameters"
         )
-        pos_args: list[FunctionType.Argument] = []
-        args: list[FunctionType.Argument] = []
-        kw_args: list[FunctionType.Argument] = []
+        pos: list[FunctionType.Parameter] = []
+        mixed: list[FunctionType.Parameter] = []
+        kw: list[FunctionType.Parameter] = []
 
-        args_first_tokens: list[Token] = []
+        mixed_first_tokens: list[Token] = []
 
         section: int = 0
         while not self.is_at_end() and not self.check(TokenType.RIGHT_PAREN):
             match section:
                 case 0 if self.match(TokenType.SLASH):
-                    pos_args = args
-                    args = []
-                    args_first_tokens = []
+                    pos = mixed
+                    mixed = []
+                    mixed_first_tokens = []
                     section = 1
                 case 0 | 1 if self.match(TokenType.STAR):
                     section = 2
                 case _:
-                    # Record first token of mixed argument for errors if unnamed
+                    # Record first token of mixed parameters for errors if unnamed
                     if section != 2:
-                        args_first_tokens.append(self.peek())
+                        mixed_first_tokens.append(self.peek())
 
                     name: Optional[Token] = None
                     if section == 2:
-                        name = self.consume_identifier("Expected keyword argument name")
+                        name = self.consume_identifier(
+                            "Expected keyword parameter name"
+                        )
                         self.consume(
-                            TokenType.COLON, "Expected ':' after argument name"
+                            TokenType.COLON, "Expected ':' after parameter name"
                         )
                     elif self.check_identifier() and self.check_next(TokenType.COLON):
                         name = self.advance()
@@ -574,24 +851,24 @@ class MidasParser(Parser):
 
                     type: Type = self.type_expr()
                     optional: bool = self.match(TokenType.QMARK)
-                    arg = FunctionType.Argument(
+                    param = FunctionType.Parameter(
                         location=None,
                         name=name,
                         type=type,
                         required=not optional,
                     )
                     if section == 2:
-                        kw_args.append(arg)
+                        kw.append(param)
                     else:
-                        args.append(arg)
+                        mixed.append(param)
 
             if not self.match(TokenType.COMMA):
                 break
 
-        for arg, token in zip(args, args_first_tokens):
-            if arg.name is None:
+        for param, token in zip(mixed, mixed_first_tokens):
+            if param.name is None:
                 # Not raised because we can keep parsing
-                self.error(token, "Unnamed mixed argument")
+                self.error(token, "Unnamed mixed parameter")
 
         self.consume(TokenType.RIGHT_PAREN, "Expected ')' after function parameters")
-        return ParamSpec(l_paren=l_paren, pos=pos_args, mixed=args, kw=kw_args)
+        return ParamSpec(l_paren=l_paren, pos=pos, mixed=mixed, kw=kw)

midas/parser/python.py

@@ -16,13 +16,17 @@ from midas.ast.python import (
     ForStmt,
     FrameColumn,
     FrameType,
+    FromImportStmt,
     Function,
     GetExpr,
     IfStmt,
+    ImportAlias,
+    ImportStmt,
     ListExpr,
     LiteralExpr,
     LogicalExpr,
     MidasType,
+    ParamSpec,
     RawExpr,
     RawStmt,
     ReturnStmt,
@@ -30,6 +34,7 @@ from midas.ast.python import (
     Stmt,
     SubscriptExpr,
     TernaryExpr,
+    TupleExpr,
     TypeAssign,
     UnaryExpr,
     VariableExpr,
@@ -48,6 +53,8 @@ class UnsupportedSyntaxError(Exception):
 
 
 class PythonParser:
+    """A parser to convert raw Python `ast` nodes in custom IR nodes"""
+
     CAST_FUNCTION = "cast"
     UNSAFE_CAST_FUNCTION = "unsafe_cast"
 
@@ -101,10 +108,34 @@ class PythonParser:
             case ast.For(orelse=[]):
                 return self.parse_for(node)
 
+            case ast.Import(names=imports):
+                return ImportStmt(
+                    location=location,
+                    imports=self._parse_imports(imports),
+                )
+
+            case ast.ImportFrom(module=module, names=imports, level=level):
+                return FromImportStmt(
+                    location=location,
+                    module=module,
+                    imports=self._parse_imports(imports),
+                    level=level,
+                )
+
             case _:
                 print(f"Unsupported statement: {ast.unparse(node)}")
                 return RawStmt(location=location, stmt=node)
 
+    def _parse_imports(self, imports: list[ast.alias]) -> list[ImportAlias]:
+        return [
+            ImportAlias(
+                location=Location.from_ast(import_),
+                name=import_.name,
+                alias=import_.asname,
+            )
+            for import_ in imports
+        ]
+
     def parse_annotation_assign(self, node: ast.AnnAssign) -> list[Stmt]:
         statements: list[Stmt] = []
         loc: Location = Location.from_ast(node)
@@ -211,27 +242,10 @@ class PythonParser:
         match node:
             case ast.FunctionDef(
                 name=name,
-                args=ast.arguments(
-                    posonlyargs=posonlyargs,
-                    args=args,
-                    vararg=sink,
-                    kwonlyargs=kwonlyargs,
-                    kwarg=kw_sink,
-                    defaults=defaults,
-                    kw_defaults=kw_defaults,
-                ),
+                args=args,
                 returns=returns,
                 body=raw_body,
             ):
-
-                def parse_args(
-                    args_list: list[ast.arg], defaults: list[Optional[Expr]]
-                ) -> list[Function.Argument]:
-                    return [
-                        self._parse_function_argument(arg, default)
-                        for arg, default in zip(args_list, defaults)
-                    ]
-
                 body: list[Stmt] = []
                 for stmt in raw_body:
                     stmts = self.parse_stmt(stmt)
@@ -240,54 +254,58 @@ class PythonParser:
                     elif stmts is not None:
                         body.extend(stmts)
 
-                parsed_defaults: list[Optional[Expr]] = [
-                    self.parse_expr(default) for default in defaults
-                ]
-                n_posargs: int = len(posonlyargs)
-                n_args: int = len(args)
-                n_all_posargs = n_posargs + n_args
-                parsed_defaults = [
-                    None,
-                ] * (n_all_posargs - len(defaults)) + parsed_defaults
-
-                posargs_defaults: list[Optional[Expr]] = parsed_defaults[:n_posargs]
-                args_defaults: list[Optional[Expr]] = parsed_defaults[n_posargs:]
-                kwargs_defaults: list[Optional[Expr]] = [
-                    self.parse_expr(default) if default is not None else None
-                    for default in kw_defaults
-                ]
-
                 return Function(
                     location=loc,
                     name=name,
-                    posonlyargs=parse_args(posonlyargs, posargs_defaults),
-                    args=parse_args(args, args_defaults),
-                    sink=(
-                        self._parse_function_argument(sink, None)
-                        if sink is not None
-                        else None
-                    ),
-                    kwonlyargs=parse_args(kwonlyargs, kwargs_defaults),
-                    kw_sink=(
-                        self._parse_function_argument(kw_sink, None)
-                        if kw_sink is not None
-                        else None
-                    ),
+                    params=self._parse_param_spec(args),
                     returns=self._parse_type(returns) if returns is not None else None,
                     body=body,
                 )
             case _:
                 print(f"Unsupported function definition: {ast.unparse(node)}")
 
-    def _parse_function_argument(
+    def _parse_param_spec(self, args: ast.arguments) -> ParamSpec:
+        def parse_params(
+            args_list: list[ast.arg], defaults: list[Optional[Expr]]
+        ) -> list[Function.Parameter]:
+            return [
+                self._parse_function_parameter(arg, default)
+                for arg, default in zip(args_list, defaults)
+            ]
+
+        defaults: list[ast.expr] = args.defaults
+        parsed_defaults: list[Optional[Expr]] = [
+            self.parse_expr(default) for default in defaults
+        ]
+        n_pos: int = len(args.posonlyargs)
+        n_mixed: int = len(args.args)
+        n_all_pos = n_pos + n_mixed
+        parsed_defaults = [
+            None,
+        ] * (n_all_pos - len(defaults)) + parsed_defaults
+
+        pos_defaults: list[Optional[Expr]] = parsed_defaults[:n_pos]
+        mixed_defaults: list[Optional[Expr]] = parsed_defaults[n_pos:]
+        kw_defaults: list[Optional[Expr]] = [
+            self.parse_expr(default) if default is not None else None
+            for default in args.kw_defaults
+        ]
+
+        return ParamSpec(
+            pos=parse_params(args.posonlyargs, pos_defaults),
+            mixed=parse_params(args.args, mixed_defaults),
+            kw=parse_params(args.kwonlyargs, kw_defaults),
+        )
+
+    def _parse_function_parameter(
         self, arg: ast.arg, default: Optional[Expr]
-    ) -> Function.Argument:
+    ) -> Function.Parameter:
         loc: Location = Location.from_ast(arg)
         name: str = arg.arg
         type: Optional[MidasType] = None
         if arg.annotation is not None:
             type = self._parse_type(arg.annotation)
-        return Function.Argument(
+        return Function.Parameter(
             location=loc,
             name=name,
             type=type,
@@ -300,26 +318,28 @@ class PythonParser:
             case ast.Subscript(value=ast.Name(id="Frame"), slice=schema):
                 return self._parse_frame_type(schema)
 
-            case ast.Subscript(value=ast.Name(id=name), slice=param):
+            case ast.Subscript(value=ast.Name(id=name), slice=arg):
+                args: tuple[MidasType, ...] = (
+                    tuple(self._parse_type(a) for a in arg.elts)
+                    if isinstance(arg, ast.Tuple)
+                    else (self._parse_type(arg),)
+                )
                 return BaseType(
                     location=loc,
                     base=name,
-                    param=self._parse_type(param),
+                    args=args,
                 )
 
             case ast.Name(id=name):
                 return BaseType(
                     location=loc,
                     base=name,
-                    param=None,
+                    args=(),
                 )
 
             case ast.BinOp(left=left_expr, op=ast.Add(), right=right_expr):
                 left = self._parse_type(left_expr)
                 match left:
-                    case None:
-                        raise InvalidSyntaxError()
-
                     # If chained constraints, separate base type and rebuild constraint
                     case ConstraintType(type=left_type, constraint=left_constraint):
                         constraint = ast.BinOp(
@@ -345,7 +365,7 @@ class PythonParser:
                 return BaseType(
                     location=loc,
                     base="None",
-                    param=None,
+                    args=(),
                 )
 
             case _:
@@ -477,6 +497,12 @@ class PythonParser:
                     step=self.parse_expr(step) if step is not None else None,
                 )
 
+            case ast.Tuple(elts=items):
+                return TupleExpr(
+                    location=location,
+                    items=tuple(self.parse_expr(item) for item in items),
+                )
+
             case _:
                 print(f"Unsupported expression: {ast.unparse(node)}")
                 return RawExpr(location=location, expr=node)

midas/typing.py

@@ -1,5 +1,8 @@
+from typing import Generic, TypeVar
 from typing import cast as typing_cast
 
+from pandas import DataFrame, Series
+
 cast = typing_cast
 """### Midas documentation
 Cast a value to a type.
@@ -32,3 +35,20 @@ This operation is unsound, use at your own risk!
 
 _**Internal Python documentation**_
 """
+
+
+T = TypeVar("T")
+
+
+class Frame(DataFrame, Generic[T]):
+    """A `Frame` is the abstract type implemented by `DataFrame`
+
+    A frame contains any number of named columns (see :class:`Column`)
+    """
+
+
+class Column(Series, Generic[T]):
+    """A `Column` is the abstract type implemented by `Series`
+
+    A column contains a any number of values of the same type
+    """

midas/utils.py

@@ -3,6 +3,7 @@ from typing import Any, Callable, Optional
 
 import midas.ast.python as p
 from midas.checker.types import Type
+from midas.generator.collector import AssertionCollector
 
 AllowRepeat = Callable[[object], bool]
 
@@ -63,3 +64,4 @@ class TypedAST:
     stmts: list[p.Stmt]
     judgements: list[tuple[p.Expr, Type]]
     evaluated_casts: list[p.CastExpr]
+    assertions: AssertionCollector

tests/__main__.py

@@ -0,0 +1,43 @@
+from typing import Type
+
+from midas.cli.ansi import Ansi
+from tests.base import Tester
+from tests.checker import CheckerTester
+from tests.generator import GeneratorTester
+from tests.midas import MidasTester
+from tests.python import PythonTester
+
+
+def print_banner(name: str):
+    horizontal: str = "+" + "-" * (len(name) + 2) + "+"
+    print(horizontal)
+    print(f"| {name} |")
+    print(horizontal)
+
+
+def run_tests(tester_cls: Type[Tester]) -> bool:
+    print_banner(tester_cls.__name__)
+    tester: Tester = tester_cls()
+    success: bool = tester.run_all_tests()
+    print()
+    return success
+
+
+def main():
+    testers: list[Type[Tester]] = [
+        PythonTester,
+        MidasTester,
+        CheckerTester,
+        GeneratorTester,
+    ]
+
+    success: bool = all(list(map(run_tests, testers)))  # list to avoid early stop
+
+    if success:
+        print(Ansi.FG(Ansi.BRIGHT_GREEN) + "All tests passed!" + Ansi.RESET)
+    else:
+        print(Ansi.FG(Ansi.BRIGHT_RED) + "Some tests failed!" + Ansi.RESET)
+
+
+if __name__ == "__main__":
+    main()

tests/base.py

@@ -7,6 +7,8 @@ from abc import ABC, abstractmethod
 from pathlib import Path
 from typing import Iterator, Protocol
 
+from midas.cli.ansi import Ansi
+
 
 class CaseResult(Protocol):
     def dumps(self) -> str: ...
@@ -44,8 +46,11 @@ class Tester(ABC):
 
         print(rule)
         for i, test in enumerate(tests):
-            print(f"Case {i+1}/{n}: {test.resolve().relative_to(self.CASES_DIR)}")
+            path: Path = test.resolve().relative_to(self.CASES_DIR)
+            print(f"{Ansi.FG(Ansi.BRIGHT_CYAN)}Case {i+1}/{n}: {path}{Ansi.RESET}")
+            print(Ansi.DIM, end="")
             success: bool = self._run_test(test)
+            print(Ansi.RESET, end="")
             if success:
                 successes += 1
             else:
@@ -146,8 +151,9 @@ class Tester(ABC):
                 if not success:
                     sys.exit(1)
             case None:
-                print("No subcommand provided. Available subcommands: run, update")
-                sys.exit(1)
+                success: bool = tester.run_all_tests()
+                if not success:
+                    sys.exit(1)
             case _:
                 print(f"Unknown subcommand '{args.subcommand}'")
                 sys.exit(1)

tests/cases/checker/01_simple_types.py.ref.json

@@ -4,7 +4,35 @@
       "type": "Warning",
       "location": {
         "start": [
-          6,
+          8,
+          12
+        ],
+        "end": [
+          8,
+          43
+        ]
+      },
+      "message": "ConstraintType not yet supported"
+    },
+    {
+      "type": "Warning",
+      "location": {
+        "start": [
+          10,
+          10
+        ],
+        "end": [
+          10,
+          18
+        ]
+      },
+      "message": "Unknown type 'datetime'"
+    },
+    {
+      "type": "Warning",
+      "location": {
+        "start": [
+          13,
           4
         ],
         "end": [
@@ -12,7 +40,7 @@
           5
         ]
       },
-      "message": "FrameType not yet supported"
+      "message": "Unknown type '_'"
     }
   ],
   "judgments": []

tests/cases/checker/04_custom_types.py.ref.json

@@ -24,7 +24,7 @@
         "type": {
           "_type": "BaseType",
           "base": "Meter",
-          "param": null
+          "args": []
         },
         "expr": {
           "_type": "LiteralExpr",
@@ -62,7 +62,7 @@
         "type": {
           "_type": "BaseType",
           "base": "Second",
-          "param": null
+          "args": []
         },
         "expr": {
           "_type": "LiteralExpr",

tests/cases/checker/06_subtyping.py.ref.json

@@ -100,41 +100,6 @@
         "name": "float"
       }
     },
-    {
-      "location": {
-        "from": "L11:5",
-        "to": "L11:12"
-      },
-      "expr": {
-        "_type": "VariableExpr",
-        "name": "maximum"
-      },
-      "type": {
-        "pos_args": [],
-        "args": [
-          {
-            "pos": 0,
-            "name": "a",
-            "type": {
-              "name": "float"
-            },
-            "required": true
-          },
-          {
-            "pos": 1,
-            "name": "b",
-            "type": {
-              "name": "float"
-            },
-            "required": true
-          }
-        ],
-        "kw_args": [],
-        "returns": {
-          "name": "float"
-        }
-      }
-    },
     {
       "location": {
         "from": "L11:13",
@@ -161,6 +126,45 @@
         "name": "float"
       }
     },
+    {
+      "location": {
+        "from": "L11:5",
+        "to": "L11:12"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "maximum"
+      },
+      "type": {
+        "params": {
+          "pos": [],
+          "mixed": [
+            {
+              "pos": 0,
+              "name": "a",
+              "type": {
+                "name": "float"
+              },
+              "required": true,
+              "unsupported": false
+            },
+            {
+              "pos": 1,
+              "name": "b",
+              "type": {
+                "name": "float"
+              },
+              "required": true,
+              "unsupported": false
+            }
+          ],
+          "kw": []
+        },
+        "returns": {
+          "name": "float"
+        }
+      }
+    },
     {
       "location": {
         "from": "L11:5",

tests/cases/checker/07_variance.py.ref.json

@@ -72,29 +72,6 @@
     }
   ],
   "judgments": [
-    {
-      "location": {
-        "from": "L26:0",
-        "to": "L26:5"
-      },
-      "expr": {
-        "_type": "VariableExpr",
-        "name": "print"
-      },
-      "type": {
-        "pos_args": [
-          {
-            "pos": 0,
-            "name": "object",
-            "type": {},
-            "required": true
-          }
-        ],
-        "args": [],
-        "kw_args": [],
-        "returns": {}
-      }
-    },
     {
       "location": {
         "from": "L27:4",
@@ -325,6 +302,32 @@
         }
       }
     },
+    {
+      "location": {
+        "from": "L26:0",
+        "to": "L26:5"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "print"
+      },
+      "type": {
+        "params": {
+          "pos": [
+            {
+              "pos": 0,
+              "name": "object",
+              "type": {},
+              "required": false,
+              "unsupported": false
+            }
+          ],
+          "mixed": [],
+          "kw": []
+        },
+        "returns": {}
+      }
+    },
     {
       "location": {
         "from": "L26:0",

tests/cases/checker/08_unification.py.ref.json

@@ -63,31 +63,6 @@
         "name": "float"
       }
     },
-    {
-      "location": {
-        "from": "L6:11",
-        "to": "L6:15"
-      },
-      "expr": {
-        "_type": "VariableExpr",
-        "name": "bool"
-      },
-      "type": {
-        "pos_args": [
-          {
-            "pos": 0,
-            "name": "object",
-            "type": {},
-            "required": false
-          }
-        ],
-        "args": [],
-        "kw_args": [],
-        "returns": {
-          "name": "bool"
-        }
-      }
-    },
     {
       "location": {
         "from": "L6:16",
@@ -135,6 +110,34 @@
         "name": "int"
       }
     },
+    {
+      "location": {
+        "from": "L6:11",
+        "to": "L6:15"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "bool"
+      },
+      "type": {
+        "params": {
+          "pos": [
+            {
+              "pos": 0,
+              "name": "object",
+              "type": {},
+              "required": false,
+              "unsupported": false
+            }
+          ],
+          "mixed": [],
+          "kw": []
+        },
+        "returns": {
+          "name": "bool"
+        }
+      }
+    },
     {
       "location": {
         "from": "L6:11",
@@ -367,94 +370,6 @@
         }
       }
     },
-    {
-      "location": {
-        "from": "L12:17",
-        "to": "L12:20"
-      },
-      "expr": {
-        "_type": "VariableExpr",
-        "name": "map"
-      },
-      "type": {
-        "name": "map",
-        "params": [
-          {
-            "name": "T",
-            "bound": null,
-            "variance": "INVARIANT"
-          },
-          {
-            "name": "U",
-            "bound": null,
-            "variance": "INVARIANT"
-          }
-        ],
-        "body": {
-          "pos_args": [
-            {
-              "pos": 0,
-              "name": "transform",
-              "type": {
-                "pos_args": [
-                  {
-                    "pos": 0,
-                    "name": "v",
-                    "type": {
-                      "name": "T",
-                      "bound": null,
-                      "variance": "INVARIANT"
-                    },
-                    "required": true
-                  }
-                ],
-                "args": [],
-                "kw_args": [],
-                "returns": {
-                  "name": "U",
-                  "bound": null,
-                  "variance": "INVARIANT"
-                }
-              },
-              "required": true
-            },
-            {
-              "pos": 1,
-              "name": "iterable",
-              "type": {
-                "name": "list",
-                "args": [
-                  {
-                    "name": "T",
-                    "bound": null,
-                    "variance": "INVARIANT"
-                  }
-                ],
-                "body": {
-                  "name": "list"
-                }
-              },
-              "required": true
-            }
-          ],
-          "args": [],
-          "kw_args": [],
-          "returns": {
-            "name": "list",
-            "args": [
-              {
-                "name": "U",
-                "bound": null,
-                "variance": "INVARIANT"
-              }
-            ],
-            "body": {
-              "name": "list"
-            }
-          }
-        }
-      }
-    },
     {
       "location": {
         "from": "L12:21",
@@ -465,18 +380,21 @@
         "name": "double"
       },
       "type": {
-        "pos_args": [],
-        "args": [
-          {
-            "pos": 0,
-            "name": "value",
-            "type": {
-              "name": "float"
-            },
-            "required": true
-          }
-        ],
-        "kw_args": [],
+        "params": {
+          "pos": [],
+          "mixed": [
+            {
+              "pos": 0,
+              "name": "value",
+              "type": {
+                "name": "float"
+              },
+              "required": true,
+              "unsupported": false
+            }
+          ],
+          "kw": []
+        },
         "returns": {
           "name": "float"
         }
@@ -503,6 +421,101 @@
         }
       }
     },
+    {
+      "location": {
+        "from": "L12:17",
+        "to": "L12:20"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "map"
+      },
+      "type": {
+        "name": "map",
+        "params": [
+          {
+            "name": "T",
+            "bound": null,
+            "variance": "INVARIANT"
+          },
+          {
+            "name": "U",
+            "bound": null,
+            "variance": "INVARIANT"
+          }
+        ],
+        "body": {
+          "params": {
+            "pos": [
+              {
+                "pos": 0,
+                "name": "transform",
+                "type": {
+                  "params": {
+                    "pos": [
+                      {
+                        "pos": 0,
+                        "name": "v",
+                        "type": {
+                          "name": "T",
+                          "bound": null,
+                          "variance": "INVARIANT"
+                        },
+                        "required": true,
+                        "unsupported": false
+                      }
+                    ],
+                    "mixed": [],
+                    "kw": []
+                  },
+                  "returns": {
+                    "name": "U",
+                    "bound": null,
+                    "variance": "INVARIANT"
+                  }
+                },
+                "required": true,
+                "unsupported": false
+              },
+              {
+                "pos": 1,
+                "name": "iterable",
+                "type": {
+                  "name": "list",
+                  "args": [
+                    {
+                      "name": "T",
+                      "bound": null,
+                      "variance": "INVARIANT"
+                    }
+                  ],
+                  "body": {
+                    "name": "list"
+                  }
+                },
+                "required": true,
+                "unsupported": false
+              }
+            ],
+            "mixed": [],
+            "kw": []
+          },
+          "returns": {
+            "name": "list",
+            "args": [
+              {
+                "name": "U",
+                "bound": null,
+                "variance": "INVARIANT"
+              }
+            ],
+            "body": {
+              "name": "list"
+            }
+          }
+        }
+      }
+    },
     {
       "location": {
         "from": "L12:17",
@@ -538,94 +551,6 @@
         }
       }
     },
-    {
-      "location": {
-        "from": "L13:15",
-        "to": "L13:18"
-      },
-      "expr": {
-        "_type": "VariableExpr",
-        "name": "map"
-      },
-      "type": {
-        "name": "map",
-        "params": [
-          {
-            "name": "T",
-            "bound": null,
-            "variance": "INVARIANT"
-          },
-          {
-            "name": "U",
-            "bound": null,
-            "variance": "INVARIANT"
-          }
-        ],
-        "body": {
-          "pos_args": [
-            {
-              "pos": 0,
-              "name": "transform",
-              "type": {
-                "pos_args": [
-                  {
-                    "pos": 0,
-                    "name": "v",
-                    "type": {
-                      "name": "T",
-                      "bound": null,
-                      "variance": "INVARIANT"
-                    },
-                    "required": true
-                  }
-                ],
-                "args": [],
-                "kw_args": [],
-                "returns": {
-                  "name": "U",
-                  "bound": null,
-                  "variance": "INVARIANT"
-                }
-              },
-              "required": true
-            },
-            {
-              "pos": 1,
-              "name": "iterable",
-              "type": {
-                "name": "list",
-                "args": [
-                  {
-                    "name": "T",
-                    "bound": null,
-                    "variance": "INVARIANT"
-                  }
-                ],
-                "body": {
-                  "name": "list"
-                }
-              },
-              "required": true
-            }
-          ],
-          "args": [],
-          "kw_args": [],
-          "returns": {
-            "name": "list",
-            "args": [
-              {
-                "name": "U",
-                "bound": null,
-                "variance": "INVARIANT"
-              }
-            ],
-            "body": {
-              "name": "list"
-            }
-          }
-        }
-      }
-    },
     {
       "location": {
         "from": "L13:19",
@@ -636,18 +561,21 @@
         "name": "double"
       },
       "type": {
-        "pos_args": [],
-        "args": [
-          {
-            "pos": 0,
-            "name": "value",
-            "type": {
-              "name": "float"
-            },
-            "required": true
-          }
-        ],
-        "kw_args": [],
+        "params": {
+          "pos": [],
+          "mixed": [
+            {
+              "pos": 0,
+              "name": "value",
+              "type": {
+                "name": "float"
+              },
+              "required": true,
+              "unsupported": false
+            }
+          ],
+          "kw": []
+        },
         "returns": {
           "name": "float"
         }
@@ -674,6 +602,101 @@
         }
       }
     },
+    {
+      "location": {
+        "from": "L13:15",
+        "to": "L13:18"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "map"
+      },
+      "type": {
+        "name": "map",
+        "params": [
+          {
+            "name": "T",
+            "bound": null,
+            "variance": "INVARIANT"
+          },
+          {
+            "name": "U",
+            "bound": null,
+            "variance": "INVARIANT"
+          }
+        ],
+        "body": {
+          "params": {
+            "pos": [
+              {
+                "pos": 0,
+                "name": "transform",
+                "type": {
+                  "params": {
+                    "pos": [
+                      {
+                        "pos": 0,
+                        "name": "v",
+                        "type": {
+                          "name": "T",
+                          "bound": null,
+                          "variance": "INVARIANT"
+                        },
+                        "required": true,
+                        "unsupported": false
+                      }
+                    ],
+                    "mixed": [],
+                    "kw": []
+                  },
+                  "returns": {
+                    "name": "U",
+                    "bound": null,
+                    "variance": "INVARIANT"
+                  }
+                },
+                "required": true,
+                "unsupported": false
+              },
+              {
+                "pos": 1,
+                "name": "iterable",
+                "type": {
+                  "name": "list",
+                  "args": [
+                    {
+                      "name": "T",
+                      "bound": null,
+                      "variance": "INVARIANT"
+                    }
+                  ],
+                  "body": {
+                    "name": "list"
+                  }
+                },
+                "required": true,
+                "unsupported": false
+              }
+            ],
+            "mixed": [],
+            "kw": []
+          },
+          "returns": {
+            "name": "list",
+            "args": [
+              {
+                "name": "U",
+                "bound": null,
+                "variance": "INVARIANT"
+              }
+            ],
+            "body": {
+              "name": "list"
+            }
+          }
+        }
+      }
+    },
     {
       "location": {
         "from": "L13:15",
@@ -699,94 +722,6 @@
       },
       "type": {}
     },
-    {
-      "location": {
-        "from": "L14:11",
-        "to": "L14:14"
-      },
-      "expr": {
-        "_type": "VariableExpr",
-        "name": "map"
-      },
-      "type": {
-        "name": "map",
-        "params": [
-          {
-            "name": "T",
-            "bound": null,
-            "variance": "INVARIANT"
-          },
-          {
-            "name": "U",
-            "bound": null,
-            "variance": "INVARIANT"
-          }
-        ],
-        "body": {
-          "pos_args": [
-            {
-              "pos": 0,
-              "name": "transform",
-              "type": {
-                "pos_args": [
-                  {
-                    "pos": 0,
-                    "name": "v",
-                    "type": {
-                      "name": "T",
-                      "bound": null,
-                      "variance": "INVARIANT"
-                    },
-                    "required": true
-                  }
-                ],
-                "args": [],
-                "kw_args": [],
-                "returns": {
-                  "name": "U",
-                  "bound": null,
-                  "variance": "INVARIANT"
-                }
-              },
-              "required": true
-            },
-            {
-              "pos": 1,
-              "name": "iterable",
-              "type": {
-                "name": "list",
-                "args": [
-                  {
-                    "name": "T",
-                    "bound": null,
-                    "variance": "INVARIANT"
-                  }
-                ],
-                "body": {
-                  "name": "list"
-                }
-              },
-              "required": true
-            }
-          ],
-          "args": [],
-          "kw_args": [],
-          "returns": {
-            "name": "list",
-            "args": [
-              {
-                "name": "U",
-                "bound": null,
-                "variance": "INVARIANT"
-              }
-            ],
-            "body": {
-              "name": "list"
-            }
-          }
-        }
-      }
-    },
     {
       "location": {
         "from": "L14:15",
@@ -797,18 +732,21 @@
         "name": "is_odd"
       },
       "type": {
-        "pos_args": [],
-        "args": [
-          {
-            "pos": 0,
-            "name": "value",
-            "type": {
-              "name": "int"
-            },
-            "required": true
-          }
-        ],
-        "kw_args": [],
+        "params": {
+          "pos": [],
+          "mixed": [
+            {
+              "pos": 0,
+              "name": "value",
+              "type": {
+                "name": "int"
+              },
+              "required": true,
+              "unsupported": false
+            }
+          ],
+          "kw": []
+        },
         "returns": {
           "name": "bool"
         }
@@ -835,6 +773,101 @@
         }
       }
     },
+    {
+      "location": {
+        "from": "L14:11",
+        "to": "L14:14"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "map"
+      },
+      "type": {
+        "name": "map",
+        "params": [
+          {
+            "name": "T",
+            "bound": null,
+            "variance": "INVARIANT"
+          },
+          {
+            "name": "U",
+            "bound": null,
+            "variance": "INVARIANT"
+          }
+        ],
+        "body": {
+          "params": {
+            "pos": [
+              {
+                "pos": 0,
+                "name": "transform",
+                "type": {
+                  "params": {
+                    "pos": [
+                      {
+                        "pos": 0,
+                        "name": "v",
+                        "type": {
+                          "name": "T",
+                          "bound": null,
+                          "variance": "INVARIANT"
+                        },
+                        "required": true,
+                        "unsupported": false
+                      }
+                    ],
+                    "mixed": [],
+                    "kw": []
+                  },
+                  "returns": {
+                    "name": "U",
+                    "bound": null,
+                    "variance": "INVARIANT"
+                  }
+                },
+                "required": true,
+                "unsupported": false
+              },
+              {
+                "pos": 1,
+                "name": "iterable",
+                "type": {
+                  "name": "list",
+                  "args": [
+                    {
+                      "name": "T",
+                      "bound": null,
+                      "variance": "INVARIANT"
+                    }
+                  ],
+                  "body": {
+                    "name": "list"
+                  }
+                },
+                "required": true,
+                "unsupported": false
+              }
+            ],
+            "mixed": [],
+            "kw": []
+          },
+          "returns": {
+            "name": "list",
+            "args": [
+              {
+                "name": "U",
+                "bound": null,
+                "variance": "INVARIANT"
+              }
+            ],
+            "body": {
+              "name": "list"
+            }
+          }
+        }
+      }
+    },
     {
       "location": {
         "from": "L14:11",

tests/cases/checker/09_frame_ops.py

@@ -0,0 +1,117 @@
+# type: ignore
+# ruff: disable [F821]
+
+df1: Frame[a:int, b:float]
+df2: Frame[a:int, b:float]
+
+_: Any
+
+# Arithmetic
+_ = df1 + df2
+_ = df1 - df2
+_ = df1 * df2
+_ = df1 / df2
+_ = df1 // df2
+_ = df1 % df2
+_ = df1**df2
+
+# Comparisons
+_ = df1 < df2
+_ = df1 > df2
+_ = df1 <= df2
+_ = df1 >= df2
+_ = df1 != df2
+_ = df1 == df2
+
+# Aggregate
+_ = df1.kurt()
+_ = df1.kurtosis()
+_ = df1.max()
+_ = df1.mean()
+_ = df1.median()
+_ = df1.min()
+_ = df1.mode()
+_ = df1.prod()
+_ = df1.product()
+_ = df1.std()
+_ = df1.sum()
+_ = df1.var()
+
+# Groupby
+df_gb = df1.groupby(by="a")
+
+_ = df_gb.kurt()
+_ = df_gb.max()
+_ = df_gb.mean()
+_ = df_gb.median()
+_ = df_gb.min()
+_ = df_gb.prod()
+_ = df_gb.std()
+_ = df_gb.sum()
+_ = df_gb.var()
+
+
+# Columns
+
+col1 = df1["a"]
+col2 = df1["a"]
+
+# Arithmetic
+_ = col1 + col2
+_ = col1 - col2
+_ = col1 * col2
+_ = col1 / col2
+_ = col1 // col2
+_ = col1 % col2
+_ = col1**col2
+
+# Comparisons
+_ = col1 < col2
+_ = col1 > col2
+_ = col1 <= col2
+_ = col1 >= col2
+_ = col1 != col2
+_ = col1 == col2
+
+# Aggregate
+_ = col1.kurt()
+_ = col1.kurtosis()
+_ = col1.max()
+_ = col1.mean()
+_ = col1.median()
+_ = col1.min()
+_ = col1.mode()
+_ = col1.prod()
+_ = col1.product()
+_ = col1.std()
+_ = col1.sum()
+_ = col1.var()
+
+# Groupby
+col_gb = col1.groupby(level=0)
+
+_ = col_gb.kurt()
+_ = col_gb.max()
+_ = col_gb.mean()
+_ = col_gb.median()
+_ = col_gb.min()
+_ = col_gb.prod()
+_ = col_gb.std()
+_ = col_gb.sum()
+_ = col_gb.var()
+
+# Attributes
+_ = df1.ndim  # int
+_ = df1.size  # int
+_ = df1.shape  # (int, int)
+_ = col1.ndim  # int
+_ = col1.size  # int
+_ = col1.shape  # (int)
+_ = col1.T  # Column[int]
+
+
+# Misc
+_ = df1.head()
+_ = df1.tail()
+_ = col1.head()
+_ = col1.tail()

tests/cases/generator/02_constraints.py.ref.txt

@@ -18,7 +18,7 @@ Module(
             ops=[
               Gt()],
             comparators=[
-              Constant(value=0.0)]))],
+              Constant(value=0)]))],
       decorator_list=[],
       returns=Constant(value='bool')),
     FunctionDef(
@@ -39,7 +39,7 @@ Module(
             ops=[
               Gt()],
             comparators=[
-              Constant(value=0.0)]))],
+              Constant(value=0)]))],
       decorator_list=[],
       returns=Constant(value='bool')),
     FunctionDef(
@@ -128,8 +128,8 @@ Module(
             func=Call(
               func=Name(id='__midas_in_range__'),
               args=[
-                Constant(value=100.0),
-                Constant(value=200.0)],
+                Constant(value=100),
+                Constant(value=200)],
               keywords=[]),
             args=[
               Name(id='_')],
@@ -142,8 +142,8 @@ Module(
       value=Call(
         func=Name(id='__midas_in_range__'),
         args=[
-          Constant(value=0.0),
-          Constant(value=18.0)],
+          Constant(value=0),
+          Constant(value=18)],
         keywords=[])),
     FunctionDef(
       name='__midas_p3__',
@@ -208,7 +208,7 @@ Module(
         args=[
           Name(id='__midas_a0__')],
         keywords=[]),
-      msg=Constant(value="02_constraints.py:L5:10: ConstraintError: Value does not fit constraint '_ > 0.0'")),
+      msg=Constant(value="02_constraints.py:L5:10: ConstraintError: Value does not fit constraint '_ > 0'")),
     Assign(
       targets=[
         Name(id='t1')],
@@ -284,7 +284,7 @@ Module(
         args=[
           Name(id='__midas_a2__')],
         keywords=[]),
-      msg=Constant(value="02_constraints.py:L7:10: ConstraintError: Value does not fit constraint 'in_range(100.0, 200.0)(_)'")),
+      msg=Constant(value="02_constraints.py:L7:10: ConstraintError: Value does not fit constraint 'in_range(100, 200)(_)'")),
     Assign(
       targets=[
         Name(id='t3')],

tests/cases/midas-parser/01_simple_types.midas.ref.json

@@ -2474,7 +2474,7 @@
                 "operator": "-",
                 "right": {
                   "_type": "LiteralExpr",
-                  "value": 90.0
+                  "value": 90
                 }
               },
               "operator": "<=",
@@ -2485,7 +2485,7 @@
             "operator": "<=",
             "right": {
               "_type": "LiteralExpr",
-              "value": 90.0
+              "value": 90
             }
           }
         }
@@ -2512,7 +2512,7 @@
                 "operator": "-",
                 "right": {
                   "_type": "LiteralExpr",
-                  "value": 180.0
+                  "value": 180
                 }
               },
               "operator": "<=",
@@ -2523,7 +2523,7 @@
             "operator": "<=",
             "right": {
               "_type": "LiteralExpr",
-              "value": 180.0
+              "value": 180
             }
           }
         }
@@ -2780,7 +2780,7 @@
         "operator": ">=",
         "right": {
           "_type": "LiteralExpr",
-          "value": 0.0
+          "value": 0
         }
       }
     },
@@ -2813,7 +2813,7 @@
         "operator": ">",
         "right": {
           "_type": "LiteralExpr",
-          "value": 0.0
+          "value": 0
         }
       }
     },
@@ -2848,7 +2848,7 @@
               "operator": "-",
               "right": {
                 "_type": "LiteralExpr",
-                "value": 10.0
+                "value": 10
               }
             },
             "operator": "<=",
@@ -2864,7 +2864,7 @@
           "operator": "<=",
           "right": {
             "_type": "LiteralExpr",
-            "value": 10.0
+            "value": 10
           }
         }
       }
@@ -2904,7 +2904,7 @@
           "operator": ">=",
           "right": {
             "_type": "LiteralExpr",
-            "value": 66.0
+            "value": 66
           }
         }
       }
@@ -2950,7 +2950,7 @@
                         "_type": "BinaryExpr",
                         "left": {
                           "_type": "LiteralExpr",
-                          "value": 0.0
+                          "value": 0
                         },
                         "operator": "<=",
                         "right": {
@@ -2960,7 +2960,7 @@
                       "operator": "<",
                       "right": {
                         "_type": "LiteralExpr",
-                        "value": 150.0
+                        "value": 150
                       }
                     }
                   }

tests/cases/python-parser/01_simple_types.py.ref.json

@@ -1,8 +1,16 @@
 {
   "stmts": [
     {
-      "_type": "RawStmt",
-      "stmt": "from __future__ import annotations"
+      "_type": "FromImportStmt",
+      "module": "__future__",
+      "imports": [
+        {
+          "_type": "ImportAlias",
+          "name": "annotations",
+          "alias": null
+        }
+      ],
+      "level": 0
     },
     {
       "_type": "TypeAssign",
@@ -16,7 +24,7 @@
             "type": {
               "_type": "BaseType",
               "base": "bool",
-              "param": null
+              "args": []
             }
           },
           {
@@ -25,7 +33,7 @@
             "type": {
               "_type": "BaseType",
               "base": "int",
-              "param": null
+              "args": []
             }
           },
           {
@@ -36,7 +44,7 @@
               "type": {
                 "_type": "BaseType",
                 "base": "float",
-                "param": null
+                "args": []
               },
               "constraint": "(_ > 0) + (_ < 250)"
             }
@@ -47,7 +55,7 @@
             "type": {
               "_type": "BaseType",
               "base": "str",
-              "param": null
+              "args": []
             }
           },
           {
@@ -56,7 +64,7 @@
             "type": {
               "_type": "BaseType",
               "base": "datetime",
-              "param": null
+              "args": []
             }
           },
           {
@@ -65,7 +73,7 @@
             "type": {
               "_type": "BaseType",
               "base": "float",
-              "param": null
+              "args": []
             }
           },
           {
@@ -79,7 +87,7 @@
             "type": {
               "_type": "BaseType",
               "base": "_",
-              "param": null
+              "args": []
             }
           }
         ]

tests/cases/python-parser/02_custom_types.py.ref.json

@@ -1,8 +1,16 @@
 {
   "stmts": [
     {
-      "_type": "RawStmt",
-      "stmt": "from __future__ import annotations"
+      "_type": "FromImportStmt",
+      "module": "__future__",
+      "imports": [
+        {
+          "_type": "ImportAlias",
+          "name": "annotations",
+          "alias": null
+        }
+      ],
+      "level": 0
     },
     {
       "_type": "TypeAssign",
@@ -16,7 +24,7 @@
             "type": {
               "_type": "BaseType",
               "base": "GeoLocation",
-              "param": null
+              "args": []
             }
           }
         ]
@@ -28,11 +36,13 @@
       "type": {
         "_type": "BaseType",
         "base": "Column",
-        "param": {
-          "_type": "BaseType",
-          "base": "GeoLocation",
-          "param": null
-        }
+        "args": [
+          {
+            "_type": "BaseType",
+            "base": "GeoLocation",
+            "args": []
+          }
+        ]
       }
     },
     {
@@ -65,11 +75,13 @@
       "type": {
         "_type": "BaseType",
         "base": "Column",
-        "param": {
-          "_type": "BaseType",
-          "base": "GeoLocation",
-          "param": null
-        }
+        "args": [
+          {
+            "_type": "BaseType",
+            "base": "GeoLocation",
+            "args": []
+          }
+        ]
       }
     },
     {
@@ -117,7 +129,7 @@
       "type": {
         "_type": "BaseType",
         "base": "Latitude",
-        "param": null
+        "args": []
       }
     },
     {
@@ -146,7 +158,7 @@
       "type": {
         "_type": "BaseType",
         "base": "Latitude",
-        "param": null
+        "args": []
       }
     },
     {
@@ -175,11 +187,13 @@
       "type": {
         "_type": "BaseType",
         "base": "Difference",
-        "param": {
-          "_type": "BaseType",
-          "base": "Latitude",
-          "param": null
-        }
+        "args": [
+          {
+            "_type": "BaseType",
+            "base": "Latitude",
+            "args": []
+          }
+        ]
       }
     },
     {
@@ -217,7 +231,7 @@
               "type": {
                 "_type": "BaseType",
                 "base": "int",
-                "param": null
+                "args": []
               },
               "constraint": "_ >= 0"
             }
@@ -230,7 +244,7 @@
               "type": {
                 "_type": "BaseType",
                 "base": "float",
-                "param": null
+                "args": []
               },
               "constraint": "_ >= 0"
             }
@@ -252,7 +266,7 @@
               "type": {
                 "_type": "BaseType",
                 "base": "int",
-                "param": null
+                "args": []
               },
               "constraint": "Positive"
             }
@@ -265,7 +279,7 @@
               "type": {
                 "_type": "BaseType",
                 "base": "float",
-                "param": null
+                "args": []
               },
               "constraint": "Positive"
             }

tests/cases/python-parser/03_functions.py.ref.json

@@ -1,64 +1,79 @@
 {
   "stmts": [
     {
-      "_type": "RawStmt",
-      "stmt": "from __future__ import annotations"
+      "_type": "FromImportStmt",
+      "module": "__future__",
+      "imports": [
+        {
+          "_type": "ImportAlias",
+          "name": "annotations",
+          "alias": null
+        }
+      ],
+      "level": 0
     },
     {
       "_type": "Function",
       "name": "func",
-      "posonlyargs": [],
-      "args": [
-        {
-          "name": "col1",
-          "type": {
-            "_type": "BaseType",
-            "base": "Column",
-            "param": {
-              "_type": "ConstraintType",
-              "type": {
-                "_type": "BaseType",
-                "base": "float",
-                "param": null
-              },
-              "constraint": "0 <= _ <= 1"
-            }
+      "params": {
+        "_type": "ParamSpec",
+        "pos": [],
+        "mixed": [
+          {
+            "name": "col1",
+            "type": {
+              "_type": "BaseType",
+              "base": "Column",
+              "args": [
+                {
+                  "_type": "ConstraintType",
+                  "type": {
+                    "_type": "BaseType",
+                    "base": "float",
+                    "args": []
+                  },
+                  "constraint": "0 <= _ <= 1"
+                }
+              ]
+            },
+            "default": null
           },
-          "default": null
-        },
-        {
-          "name": "col2",
-          "type": {
-            "_type": "BaseType",
-            "base": "Column",
-            "param": {
-              "_type": "ConstraintType",
-              "type": {
-                "_type": "BaseType",
-                "base": "float",
-                "param": null
-              },
-              "constraint": "0 <= _ <= 1"
-            }
-          },
-          "default": null
-        }
-      ],
-      "sink": null,
-      "kwonlyargs": [],
-      "kw_sink": null,
+          {
+            "name": "col2",
+            "type": {
+              "_type": "BaseType",
+              "base": "Column",
+              "args": [
+                {
+                  "_type": "ConstraintType",
+                  "type": {
+                    "_type": "BaseType",
+                    "base": "float",
+                    "args": []
+                  },
+                  "constraint": "0 <= _ <= 1"
+                }
+              ]
+            },
+            "default": null
+          }
+        ],
+        "kw": []
+      },
       "returns": {
         "_type": "BaseType",
         "base": "Column",
-        "param": {
-          "_type": "ConstraintType",
-          "type": {
-            "_type": "BaseType",
-            "base": "float",
-            "param": null
-          },
-          "constraint": "0 <= _ <= 2"
-        }
+        "args": [
+          {
+            "_type": "ConstraintType",
+            "type": {
+              "_type": "BaseType",
+              "base": "float",
+              "args": []
+            },
+            "constraint": "0 <= _ <= 2"
+          }
+        ]
       },
       "body": [
         {
@@ -67,15 +82,17 @@
           "type": {
             "_type": "BaseType",
             "base": "Column",
-            "param": {
-              "_type": "ConstraintType",
-              "type": {
-                "_type": "BaseType",
-                "base": "float",
-                "param": null
-              },
-              "constraint": "0 <= _ <= 2"
-            }
+            "args": [
+              {
+                "_type": "ConstraintType",
+                "type": {
+                  "_type": "BaseType",
+                  "base": "float",
+                  "args": []
+                },
+                "constraint": "0 <= _ <= 2"
+              }
+            ]
           }
         },
         {
@@ -111,41 +128,42 @@
     {
       "_type": "Function",
       "name": "func2",
-      "posonlyargs": [
-        {
-          "name": "a",
-          "type": {
-            "_type": "BaseType",
-            "base": "int",
-            "param": null
-          },
-          "default": null
-        }
-      ],
-      "args": [
-        {
-          "name": "b",
-          "type": {
-            "_type": "BaseType",
-            "base": "float",
-            "param": null
-          },
-          "default": null
-        }
-      ],
-      "sink": null,
-      "kwonlyargs": [
-        {
-          "name": "c",
-          "type": {
-            "_type": "BaseType",
-            "base": "str",
-            "param": null
-          },
-          "default": null
-        }
-      ],
-      "kw_sink": null,
+      "params": {
+        "_type": "ParamSpec",
+        "pos": [
+          {
+            "name": "a",
+            "type": {
+              "_type": "BaseType",
+              "base": "int",
+              "args": []
+            },
+            "default": null
+          }
+        ],
+        "mixed": [
+          {
+            "name": "b",
+            "type": {
+              "_type": "BaseType",
+              "base": "float",
+              "args": []
+            },
+            "default": null
+          }
+        ],
+        "kw": [
+          {
+            "name": "c",
+            "type": {
+              "_type": "BaseType",
+              "base": "str",
+              "args": []
+            },
+            "default": null
+          }
+        ]
+      },
       "returns": null,
       "body": []
     }

tests/generator.py

@@ -46,7 +46,8 @@ class GeneratorTester(Tester):
 
         if not any(d.type == DiagnosticType.ERROR for d in checker.diagnostics):
             generator = Generator(workdir=path.parent, types=checker.types)
-            result.compiled_ast = generator.generate_ast(typed_ast, path)
+            generator.set_src_path(path)
+            result.compiled_ast = generator.generate_ast(typed_ast)
 
         return result
 

tests/serializer/midas.py

@@ -1,6 +1,7 @@
 from typing import Optional, Sequence
 
 from midas.ast.midas import (
+    AliasStmt,
     BinaryExpr,
     CallExpr,
     ComplexType,
@@ -8,6 +9,7 @@ from midas.ast.midas import (
     Expr,
     ExtendStmt,
     ExtensionType,
+    FrameType,
     FunctionType,
     GenericType,
     GetExpr,
@@ -60,6 +62,13 @@ class MidasAstJsonSerializer(
             "bound": self._serialize_optional(param.bound),
         }
 
+    def visit_alias_stmt(self, stmt: AliasStmt) -> dict:
+        return {
+            "_type": "AliasStmt",
+            "name": stmt.name.lexeme,
+            "type": stmt.type.accept(self),
+        }
+
     def visit_member_stmt(self, stmt: MemberStmt) -> dict:
         return {
             "_type": "MemberStmt",
@@ -179,16 +188,16 @@ class MidasAstJsonSerializer(
     def _serialize_param_spec(self, spec: ParamSpec) -> dict:
         return {
             "_type": "ParamSpec",
-            "pos": [self._serialize_func_arg(arg) for arg in spec.pos],
-            "mixed": [self._serialize_func_arg(arg) for arg in spec.mixed],
-            "kw": [self._serialize_func_arg(arg) for arg in spec.kw],
+            "pos": [self._serialize_func_param(arg) for arg in spec.pos],
+            "mixed": [self._serialize_func_param(arg) for arg in spec.mixed],
+            "kw": [self._serialize_func_param(arg) for arg in spec.kw],
         }
 
-    def _serialize_func_arg(self, arg: FunctionType.Argument) -> dict:
+    def _serialize_func_param(self, param: FunctionType.Parameter) -> dict:
         return {
-            "name": arg.name.lexeme if arg.name is not None else None,
-            "type": arg.type.accept(self),
-            "required": arg.required,
+            "name": param.name.lexeme if param.name is not None else None,
+            "type": param.type.accept(self),
+            "required": param.required,
         }
 
     def visit_extension_type(self, type: ExtensionType) -> dict:
@@ -197,3 +206,15 @@ class MidasAstJsonSerializer(
             "base": type.base.accept(self),
             "extension": type.extension.accept(self),
         }
+
+    def visit_frame_type(self, type: FrameType) -> dict:
+        return {
+            "_type": "FrameType",
+            "columns": [self._serialize_column(col) for col in type.columns],
+        }
+
+    def _serialize_column(self, column: FrameType.Column):
+        return {
+            "name": column.name.lexeme,
+            "type": column.type.accept(self),
+        }

tests/serializer/python.py

@@ -15,13 +15,17 @@ from midas.ast.python import (
     ForStmt,
     FrameColumn,
     FrameType,
+    FromImportStmt,
     Function,
     GetExpr,
     IfStmt,
+    ImportAlias,
+    ImportStmt,
     ListExpr,
     LiteralExpr,
     LogicalExpr,
     MidasType,
+    ParamSpec,
     Pass,
     RawExpr,
     RawStmt,
@@ -30,6 +34,7 @@ from midas.ast.python import (
     Stmt,
     SubscriptExpr,
     TernaryExpr,
+    TupleExpr,
     TypeAssign,
     UnaryExpr,
     VariableExpr,
@@ -98,7 +103,7 @@ class PythonAstJsonSerializer(
         return {
             "_type": "BaseType",
             "base": node.base,
-            "param": self._serialize_optional(node.param),
+            "args": self._serialize_list(node.args),
         }
 
     def visit_constraint_type(self, node: ConstraintType) -> dict:
@@ -127,32 +132,30 @@ class PythonAstJsonSerializer(
             "expr": stmt.expr.accept(self),
         }
 
-    def _serialize_argument(self, arg: Function.Argument) -> dict:
-        return {
-            "name": arg.name,
-            "type": self._serialize_optional(arg.type),
-            "default": self._serialize_optional(arg.default),
-        }
-
     def visit_function(self, stmt: Function) -> dict:
         return {
             "_type": "Function",
             "name": stmt.name,
-            "posonlyargs": [self._serialize_argument(arg) for arg in stmt.posonlyargs],
-            "args": [self._serialize_argument(arg) for arg in stmt.args],
-            "sink": (
-                self._serialize_argument(stmt.sink) if stmt.sink is not None else None
-            ),
-            "kwonlyargs": [self._serialize_argument(arg) for arg in stmt.kwonlyargs],
-            "kw_sink": (
-                self._serialize_argument(stmt.kw_sink)
-                if stmt.kw_sink is not None
-                else None
-            ),
+            "params": self._serialize_param_spec(stmt.params),
             "returns": self._serialize_optional(stmt.returns),
             "body": self._serialize_list(stmt.body),
         }
 
+    def _serialize_param_spec(self, spec: ParamSpec) -> dict:
+        return {
+            "_type": "ParamSpec",
+            "pos": [self._serialize_func_param(arg) for arg in spec.pos],
+            "mixed": [self._serialize_func_param(arg) for arg in spec.mixed],
+            "kw": [self._serialize_func_param(arg) for arg in spec.kw],
+        }
+
+    def _serialize_func_param(self, param: Function.Parameter) -> dict:
+        return {
+            "name": param.name,
+            "type": self._serialize_optional(param.type),
+            "default": self._serialize_optional(param.default),
+        }
+
     def visit_type_assign(self, stmt: TypeAssign) -> dict:
         return {
             "_type": "TypeAssign",
@@ -194,6 +197,30 @@ class PythonAstJsonSerializer(
             "body": self._serialize_list(stmt.body),
         }
 
+    def visit_import_stmt(self, stmt: ImportStmt) -> dict:
+        return {
+            "_type": "ImportStmt",
+            "imports": self._serialize_imports(stmt.imports),
+        }
+
+    def visit_from_import_stmt(self, stmt: FromImportStmt) -> dict:
+        return {
+            "_type": "FromImportStmt",
+            "module": stmt.module,
+            "imports": self._serialize_imports(stmt.imports),
+            "level": stmt.level,
+        }
+
+    def _serialize_imports(self, imports: list[ImportAlias]) -> list:
+        return [
+            {
+                "_type": "ImportAlias",
+                "name": import_.name,
+                "alias": import_.alias,
+            }
+            for import_ in imports
+        ]
+
     def visit_raw_stmt(self, stmt: RawStmt) -> dict:
         return {
             "_type": "RawStmt",
@@ -302,6 +329,12 @@ class PythonAstJsonSerializer(
             "step": self._serialize_optional(expr.step),
         }
 
+    def visit_tuple_expr(self, expr: TupleExpr) -> dict:
+        return {
+            "_type": "TupleExpr",
+            "items": [item.accept(self) for item in expr.items],
+        }
+
     def visit_raw_expr(self, expr: RawExpr) -> dict:
         return {
             "_type": "RawExpr",