feat(checker): add diagnostics

still very basic but lays out the structure and help methods

docs/architecture.typ

@@ -0,0 +1,150 @@
+#import "@preview/cetz:0.5.2": canvas, draw
+
+#let diagram-only = false
+
+#set document(
+  title: [Midas Architecture],
+  //author: "Louis Heredero",
+)
+
+#set text(
+  font: "Source Sans 3",
+)
+
+#let diagram = canvas({
+  let framed = draw.content.with(
+    padding: (x: .8em, y: 1em),
+    frame: "rect",
+    stroke: black,
+  )
+  let arrow = draw.line.with(mark: (end: ">", fill: black))
+  framed(
+    (0, 0),
+    name: "python-parser",
+  )[Python parser]
+
+  draw.content(
+    (rel: (0, 1), to: "python-parser.north"),
+    padding: 5pt,
+    anchor: "south",
+    name: "source-py",
+  )[_`source.py`_]
+  arrow("source-py", "python-parser")
+
+  framed(
+    (rel: (3, 0), to: "python-parser.east"),
+    anchor: "west",
+    name: "custom-parser",
+    align(center)[Custom python\ parser],
+  )
+
+  arrow("python-parser", "custom-parser", name: "arrow-python-ast")
+  draw.content(
+    "arrow-python-ast",
+    anchor: "south",
+    padding: 5pt,
+  )[`ast.Module`]
+
+  framed(
+    (rel: (-3, -2), to: "custom-parser.south"),
+    anchor: "east",
+    name: "python-resolver",
+  )[Python Resolver]
+  arrow(
+    "custom-parser",
+    ((), "|-", "python-resolver.east"),
+    "python-resolver",
+    name: "arrow-python-custom-ast",
+  )
+  draw.content(
+    (rel: (1.5, 0), to: "arrow-python-custom-ast.end"),
+    padding: 5pt,
+    anchor: "south",
+  )[P-AST#footnote[#strong[P]ython *AST*]<fn-past>]
+  draw.content(
+    "python-resolver.west",
+    padding: 5pt,
+    anchor: "south-east",
+  )[Resolved P-AST@fn-past]
+
+  draw.circle(
+    (rel: (1, -2), to: "custom-parser.south-east"),
+    radius: .4,
+    name: "midas-loader",
+  )
+  arrow(
+    "custom-parser",
+    "midas-loader",
+    name: "arrow-load-midas",
+    mark: (end: (symbol: ">", fill: black), start: "o"),
+  )
+  draw.content(
+    "arrow-load-midas",
+    anchor: "west",
+    padding: 5pt,
+  )[```python midas.using("types.midas")```]
+
+  framed(
+    (rel: (0, -2), to: "midas-loader.south"),
+    name: "midas-parser",
+  )[Midas lexer/parser]
+  arrow("midas-loader", "midas-parser", name: "arrow-midas-source")
+  draw.content(
+    "arrow-midas-source",
+    anchor: "west",
+    padding: 5pt,
+  )[_`types.midas`_]
+
+
+  framed(
+    (rel: (-2, 0), to: "midas-parser.west"),
+    anchor: "east",
+    name: "midas-resolver",
+  )[Midas Resolver]
+  arrow("midas-parser", "midas-resolver", name: "arrow-midas-ast")
+  draw.content(
+    "arrow-midas-ast",
+    anchor: "south",
+    padding: 5pt,
+  )[M-AST#footnote[#strong[M]idas *AST*]<fn-mast>]
+
+  framed(
+    (rel: (-3, 0), to: "midas-resolver.west"),
+    anchor: "east",
+    name: "checker",
+  )[Checker]
+  arrow("midas-resolver", "checker", name: "arrow-type-ctx")
+  arrow(
+    "python-resolver",
+    ((), "-|", "checker.north"),
+    "checker",
+  )
+  draw.content(
+    "arrow-type-ctx",
+    anchor: "south",
+    padding: 5pt,
+  )[Types context]
+})
+
+#show: doc => if diagram-only {
+  set page(width: auto, height: auto, margin: .5cm)
+  diagram
+} else { doc }
+
+#align(center, title())
+
+#v(1cm)
+
+#figure(
+  diagram,
+  caption: [Midas type-checker architecture],
+)
+
+== Components
+
+- *Python parser*: builtin Python AST parser, extracts abstract syntax from the raw Python source (```python ast.parse(...)```)
+- *Custom python parser*: converts the raw Python AST into custom, more suitable constructs, especially for type annotations
+- *Python resolver*: resolves bindings and references, tracks binding scopes
+- *Midas lexer/parser*: parses a Midas type definition file and extracts its AST
+- *Midas resolver*: walks the AST and fills the environment with the defined types and operations
+- *Checker*: evaluates expressions and checks type coherence

examples/01_simple_type_checking/01_simple_operations.py

@@ -0,0 +1,4 @@
+a: int = 3
+b: int = 4
+
+c = a + b  # -> int

examples/01_simple_type_checking/02_simple_types.midas

@@ -0,0 +1,14 @@
+type Meter(float)
+type Second(float)
+type MeterPerSecond(float)
+
+extend Meter {
+    op __add__(Meter) -> Meter
+    op __sub__(Meter) -> Meter
+    op __truediv__(Second) -> MeterPerSecond
+}
+
+extend Second {
+    op __add__(Second) -> Second
+    op __sub__(Second) -> Second
+}

examples/01_simple_type_checking/02_simple_types.py

@@ -0,0 +1,8 @@
+# type: ignore
+# ruff: disable [F821]
+
+midas.using("02_simple_types.midas")
+
+distance: Meter = 123.45
+time: Second = 6.7
+speed = distance / time

gen/gen.py

@@ -11,7 +11,7 @@ SECTION_TEMPLATE = """{banner}
 
 @dataclass(frozen=True, kw_only=True)
 class {base}(ABC):
-    location: Optional[Location] = None
+    location: Location
 
     @abstractmethod
     def accept(self, visitor: Visitor[T]) -> T: ...

gen/python.py

@@ -46,13 +46,18 @@ class Function:
     args: list[Argument]
     kwonlyargs: list[Argument]
     returns: Optional[MidasType]
+    body: list[Stmt]
 
     @dataclass(frozen=True, kw_only=True)
     class Argument:
         location: Optional[Location] = None
-        name: Optional[str]
+        name: str
         type: Optional[MidasType]
 
+    @property
+    def all_args(self) -> list[Argument]:
+        return self.posonlyargs + self.args + self.kwonlyargs
+
 
 class TypeAssign:
     name: str

midas/ast/midas.py

@@ -21,7 +21,7 @@ T = TypeVar("T")
 
 @dataclass(frozen=True, kw_only=True)
 class Stmt(ABC):
-    location: Optional[Location] = None
+    location: Location
 
     @abstractmethod
     def accept(self, visitor: Visitor[T]) -> T: ...
@@ -114,7 +114,7 @@ class PredicateStmt(Stmt):
 
 @dataclass(frozen=True, kw_only=True)
 class Expr(ABC):
-    location: Optional[Location] = None
+    location: Location
 
     @abstractmethod
     def accept(self, visitor: Visitor[T]) -> T: ...

midas/ast/python.py

@@ -21,7 +21,7 @@ T = TypeVar("T")
 
 @dataclass(frozen=True, kw_only=True)
 class MidasType(ABC):
-    location: Optional[Location] = None
+    location: Location
 
     @abstractmethod
     def accept(self, visitor: Visitor[T]) -> T: ...
@@ -82,7 +82,7 @@ class FrameType(MidasType):
 
 @dataclass(frozen=True, kw_only=True)
 class Stmt(ABC):
-    location: Optional[Location] = None
+    location: Location
 
     @abstractmethod
     def accept(self, visitor: Visitor[T]) -> T: ...
@@ -116,13 +116,18 @@ class Function(Stmt):
     args: list[Argument]
     kwonlyargs: list[Argument]
     returns: Optional[MidasType]
+    body: list[Stmt]
 
     @dataclass(frozen=True, kw_only=True)
     class Argument:
         location: Optional[Location] = None
-        name: Optional[str]
+        name: str
         type: Optional[MidasType]
 
+    @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)
 
@@ -152,7 +157,7 @@ class AssignStmt(Stmt):
 
 @dataclass(frozen=True, kw_only=True)
 class Expr(ABC):
-    location: Optional[Location] = None
+    location: Location
 
     @abstractmethod
     def accept(self, visitor: Visitor[T]) -> T: ...

midas/checker/checker.py

@@ -0,0 +1,198 @@
+import logging
+from pathlib import Path
+from typing import Optional
+
+import midas.ast.midas as m
+import midas.ast.python as p
+from midas.ast.location import Location
+from midas.checker.diagnostic import Diagnostic, DiagnosticType
+from midas.checker.environment import Environment
+from midas.checker.operators import OPERATOR_METHODS
+from midas.checker.types import Type, UnknownType
+from midas.lexer.midas import MidasLexer
+from midas.lexer.token import Token
+from midas.parser.midas import MidasParser
+from midas.resolver.midas import MidasResolver
+
+
+class Checker(
+    p.Stmt.Visitor[None],
+    p.Expr.Visitor[Type],
+    p.MidasType.Visitor[Type],
+):
+    def __init__(self, locals: dict[p.Expr, int], file_path: Path):
+        self.logger: logging.Logger = logging.getLogger("Checker")
+        self.file_path: Path = file_path
+        self.ctx: MidasResolver = MidasResolver()
+        self.global_env: Environment = Environment()
+        self.env: Environment = self.global_env
+        self.locals: dict[p.Expr, int] = locals
+        self.diagnostics: list[Diagnostic] = []
+
+    def diagnostic(self, type: DiagnosticType, location: Location, message: str):
+        self.diagnostics.append(
+            Diagnostic(
+                file_path=self.file_path,
+                location=location,
+                type=type,
+                message=message,
+            )
+        )
+
+    def error(self, location: Location, message: str):
+        self.diagnostic(
+            type=DiagnosticType.ERROR,
+            location=location,
+            message=message,
+        )
+
+    def warning(self, location: Location, message: str):
+        self.diagnostic(
+            type=DiagnosticType.WARNING,
+            location=location,
+            message=message,
+        )
+
+    def info(self, location: Location, message: str):
+        self.diagnostic(
+            type=DiagnosticType.INFO,
+            location=location,
+            message=message,
+        )
+
+    def evaluate(self, expr: p.Expr) -> Type:
+        return expr.accept(self)
+
+    def check(self, statements: list[p.Stmt]) -> list[Diagnostic]:
+        self.diagnostics = []
+        for stmt in statements:
+            stmt.accept(self)
+
+        self.logger.debug(f"Final environment: {self.env.flat_dict()}")
+        return self.diagnostics
+
+    def look_up_variable(self, name: str, expr: p.Expr) -> Optional[Type]:
+        distance: Optional[int] = self.locals.get(expr)
+        if distance is not None:
+            return self.env.get_at(distance, name)
+        return self.global_env.get(name)
+
+    def parse_midas_import(self, expr: p.CallExpr) -> Optional[Path]:
+        match expr:
+            case p.CallExpr(
+                callee=p.GetExpr(
+                    object=p.VariableExpr(name="midas"),
+                    name="using",
+                ),
+                arguments=[
+                    p.LiteralExpr(value=path),
+                ],
+            ):
+                return Path(path)
+        return None
+
+    def import_midas(self, path: Path) -> None:
+        self.logger.debug(f"Importing type definitions from {path}")
+        path = (self.file_path.parent / path).resolve()
+        lexer: MidasLexer = MidasLexer(path.read_text())
+        tokens: list[Token] = lexer.process()
+        parser: MidasParser = MidasParser(tokens)
+        stmts: list[m.Stmt] = parser.parse()
+        self.ctx.resolve(stmts)
+        self.logger.debug(f"Midas types: {self.ctx._types}")
+        self.logger.debug(f"Midas operations: {self.ctx._operations}")
+
+    def visit_expression_stmt(self, stmt: p.ExpressionStmt) -> None:
+        self.evaluate(stmt.expr)
+
+    def visit_function(self, stmt: p.Function) -> None: ...
+
+    def visit_type_assign(self, stmt: p.TypeAssign) -> None:
+        # TODO check not yet defined locally
+        type: Type = stmt.type.accept(self)
+        self.env.define(stmt.name, type)
+
+    def visit_assign_stmt(self, stmt: p.AssignStmt) -> None:
+        value: Type = self.evaluate(stmt.value)
+        for target in stmt.targets:
+            if not isinstance(target, p.VariableExpr):
+                self.logger.warning(f"Unsupported assignment to {target}")
+                self.warning(target.location, f"Unsupported assignment to {target}")
+                continue
+            name: str = target.name
+            var_type: Optional[Type] = self.look_up_variable(name, target)
+
+            if var_type is None:
+                self.env.define(name, value)
+            else:
+                # TODO: implement real comparison method
+                if var_type != value:
+                    self.error(
+                        stmt.location,
+                        f"Cannot assign {value} to {name} of type {var_type}",
+                    )
+
+    def visit_binary_expr(self, expr: p.BinaryExpr) -> Type:
+        method: Optional[str] = OPERATOR_METHODS.get(expr.operator.__class__)
+        if method is None:
+            self.logger.warning(f"Unsupported operator {expr.operator}")
+            self.warning(expr.location, f"Unsupported operator {expr.operator}")
+            return UnknownType()
+        left: Type = self.evaluate(expr.left)
+        right: Type = self.evaluate(expr.right)
+
+        result: Optional[Type] = self.ctx.get_operation_result(left, method, right)
+        if result is None:
+            self.error(
+                expr.location,
+                f"Undefined operation {method} between {left} and {right}",
+            )
+            return UnknownType()
+        return result
+
+    def visit_compare_expr(self, expr: p.CompareExpr) -> Type: ...
+
+    def visit_unary_expr(self, expr: p.UnaryExpr) -> Type: ...
+
+    def visit_call_expr(self, expr: p.CallExpr) -> Type:
+        if path := self.parse_midas_import(expr):
+            self.import_midas(path)
+            return UnknownType()
+        callee: Type = self.evaluate(expr.callee)
+        arguments: list[Type] = [self.evaluate(arg) for arg in expr.arguments]
+        keywords: dict[str, Type] = {
+            name: self.evaluate(arg) for name, arg in expr.keywords.items()
+        }
+        return UnknownType()
+
+    def visit_get_expr(self, expr: p.GetExpr) -> Type: ...
+
+    def visit_literal_expr(self, expr: p.LiteralExpr) -> Type:
+        match expr.value:
+            case bool():  # Must be before int
+                return self.ctx.get_type("bool")
+            case int():
+                return self.ctx.get_type("int")
+            case float():
+                return self.ctx.get_type("float")
+            case str():
+                return self.ctx.get_type("str")
+            case _:
+                self.warning(expr.location, f"Unknown literal {expr}")
+                return UnknownType()
+
+    def visit_variable_expr(self, expr: p.VariableExpr) -> Type:
+        return self.look_up_variable(expr.name, expr) or UnknownType()
+
+    def visit_logical_expr(self, expr: p.LogicalExpr) -> Type: ...
+
+    def visit_set_expr(self, expr: p.SetExpr) -> Type: ...
+
+    def visit_base_type(self, node: p.BaseType) -> Type:
+        return self.ctx.get_type(node.base)
+
+    def visit_constraint_type(self, node: p.ConstraintType) -> Type: ...
+
+    def visit_frame_column(self, node: p.FrameColumn) -> Type: ...
+
+    def visit_frame_type(self, node: p.FrameType) -> Type: ...

midas/checker/diagnostic.py

@@ -0,0 +1,33 @@
+from dataclasses import dataclass
+from enum import StrEnum
+from pathlib import Path
+from typing import Optional
+
+from midas.ast.location import Location
+
+
+class DiagnosticType(StrEnum):
+    ERROR = "Error"
+    WARNING = "Warning"
+    INFO = "Info"
+
+
+@dataclass(frozen=True)
+class Diagnostic:
+    file_path: Path
+    location: Location
+    type: DiagnosticType
+    message: str
+
+    def __str__(self) -> str:
+        start_loc: str = f"L{self.location.lineno}:{self.location.col_offset+1}"
+        end_loc: Optional[str] = ""
+        if (
+            self.location.end_lineno is not None
+            and self.location.end_col_offset is not None
+        ):
+            end_loc = f"L{self.location.end_lineno}:{self.location.end_col_offset+1}"
+        loc: str = (
+            f"at {start_loc}" if end_loc is None else f"from {start_loc} to {end_loc}"
+        )
+        return f"{self.type} in {self.file_path} {loc}: {self.message}"

midas/checker/environment.py

@@ -0,0 +1,52 @@
+from __future__ import annotations
+
+from typing import Optional
+
+from midas.checker.types import Type
+
+
+class Environment:
+    def __init__(self, enclosing: Optional[Environment] = None) -> None:
+        self.enclosing: Optional[Environment] = enclosing
+        self.values: dict[str, Type] = {}
+
+    def define(self, name: str, value: Type):
+        self.values[name] = value
+
+    def get(self, name: str) -> Optional[Type]:
+        if name in self.values:
+            return self.values[name]
+        if self.enclosing is not None:
+            return self.enclosing.get(name)
+        # raise NameError(f"Undefined variable '{name}'")
+        return None
+
+    def assign(self, name: str, value: Type) -> bool:
+        if name not in self.values:
+            if self.enclosing is None:
+                return False
+            if self.enclosing.assign(name, value):
+                return True
+        self.values[name] = value
+        return True
+
+    def clear(self):
+        self.values = {}
+
+    def get_at(self, distance: int, name: str) -> Optional[Type]:
+        return self.ancestor(distance).values.get(name)
+
+    def assign_at(self, distance: int, name: str, value: Type):
+        self.ancestor(distance).values[name] = value
+
+    def ancestor(self, distance: int) -> Environment:
+        env: Environment = self
+        for _ in range(distance):
+            assert env.enclosing is not None
+            env = env.enclosing
+        return env
+
+    def flat_dict(self) -> dict:
+        if self.enclosing is None:
+            return self.values
+        return self.enclosing.flat_dict() | self.values

midas/checker/operators.py

@@ -0,0 +1,31 @@
+import ast
+from typing import Type
+
+OPERATOR_METHODS: dict[Type[ast.operator], str] = {
+    ast.Add: "__add__",
+    ast.Sub: "__sub__",
+    ast.Mult: "__mul__",
+    ast.MatMult: "__matmul__",
+    ast.Div: "__truediv__",
+    ast.Mod: "__mod__",
+    ast.Pow: "__pow__",
+    ast.LShift: "__lshift__",
+    ast.RShift: "__rshift__",
+    ast.BitOr: "__or__",
+    ast.BitXor: "__xor__",
+    ast.BitAnd: "__and__",
+    ast.FloorDiv: "__floordiv__",
+}
+
+COMPARATOR_METHODS: dict[Type[ast.cmpop], str] = {
+    ast.Eq: "__eq__",
+    # ast.NotEq: "__noteq__",
+    ast.Lt: "__lt__",
+    ast.LtE: "__le__",
+    ast.Gt: "__gt__",
+    ast.GtE: "__ge__",
+    # ast.Is: "__is__",
+    # ast.IsNot: "__isnot__",
+    # ast.In: "__in__",
+    # ast.NotIn: "__notin__",
+}

midas/checker/types.py

@@ -0,0 +1,22 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+
+@dataclass(frozen=True, kw_only=True)
+class BaseType:
+    name: str
+
+
+@dataclass(frozen=True, kw_only=True)
+class SimpleType:
+    name: str
+    base: BaseType | SimpleType
+
+
+@dataclass(frozen=True, kw_only=True)
+class UnknownType:
+    pass
+
+
+Type = BaseType | SimpleType | UnknownType

midas/cli/main.py

@@ -1,5 +1,7 @@
 import ast
+import logging
 from dataclasses import dataclass
+from pathlib import Path
 from typing import Optional, TextIO
 
 import click
@@ -8,11 +10,14 @@ import midas.ast.midas as m
 import midas.ast.python as p
 from midas.ast.location import Location
 from midas.ast.printer import PythonAstPrinter
+from midas.checker.checker import Checker
+from midas.checker.diagnostic import Diagnostic
 from midas.cli.highlighter import Highlighter, MidasHighlighter, PythonHighlighter
 from midas.lexer.midas import MidasLexer
 from midas.lexer.token import Token, TokenType
 from midas.parser.midas import MidasParser
 from midas.parser.python import PythonParser
+from midas.resolver.resolver import Resolver
 
 
 @click.group()
@@ -23,7 +28,17 @@ def midas():
 @midas.command()
 @click.argument("file", type=click.File("r"))
 def compile(file: TextIO):
-    raise NotImplementedError
+    logging.basicConfig(level=logging.DEBUG)
+    source: str = file.read()
+    tree: ast.Module = ast.parse(source, filename=file.name)
+    parser = PythonParser()
+    stmts: list[p.Stmt] = parser.parse_module(tree)
+    resolver = Resolver()
+    resolver.resolve(*stmts)
+    checker = Checker(resolver.locals, file_path=Path(file.name).resolve())
+    diagnostics: list[Diagnostic] = checker.check(stmts)
+    for diagnostic in diagnostics:
+        print(diagnostic)
 
 
 @midas.group()
@@ -109,3 +124,7 @@ def highlight(output: TextIO, file: TextIO):
     else:
         raise ValueError("Unsupported file type")
     highlighter.dump(output)
+
+
+if __name__ == "__main__":
+    midas()

midas/parser/midas.py

@@ -205,9 +205,7 @@ class MidasParser(Parser):
         while self.match(TokenType.AND):
             operator: Token = self.previous()
             right: Expr = self.equality()
-            location: Optional[Location] = None
-            if expr.location and right.location:
-                location = Location.span(expr.location, right.location)
+            location: Location = Location.span(expr.location, right.location)
             expr = LogicalExpr(
                 location=location, left=expr, operator=operator, right=right
             )
@@ -223,9 +221,7 @@ class MidasParser(Parser):
         while self.match(TokenType.BANG_EQUAL, TokenType.EQUAL_EQUAL):
             operator: Token = self.previous()
             right: Expr = self.comparison()
-            location: Optional[Location] = None
-            if expr.location and right.location:
-                location = Location.span(expr.location, right.location)
+            location: Location = Location.span(expr.location, right.location)
             expr = BinaryExpr(
                 location=location, left=expr, operator=operator, right=right
             )
@@ -246,9 +242,7 @@ class MidasParser(Parser):
         ):
             operator: Token = self.previous()
             right: Expr = self.unary()
-            location: Optional[Location] = None
-            if expr.location and right.location:
-                location = Location.span(expr.location, right.location)
+            location: Location = Location.span(expr.location, right.location)
             expr = BinaryExpr(
                 location=location, left=expr, operator=operator, right=right
             )
@@ -263,9 +257,7 @@ class MidasParser(Parser):
         if self.match(TokenType.MINUS):
             operator: Token = self.previous()
             right: Expr = self.unary()
-            location: Optional[Location] = None
-            if right.location:
-                location = Location.span(operator.get_location(), right.location)
+            location: Location = Location.span(operator.get_location(), right.location)
             return UnaryExpr(location=location, operator=operator, right=right)
         return self.reference()
 
@@ -280,9 +272,7 @@ class MidasParser(Parser):
             name: Token = self.consume(
                 TokenType.IDENTIFIER, "Expected property name after '.'"
             )
-            location: Optional[Location] = None
-            if expr.location:
-                location = Location.span(expr.location, name.get_location())
+            location: Location = Location.span(expr.location, name.get_location())
             expr = GetExpr(location=location, expr=expr, name=name)
         return expr
 
@@ -370,9 +360,7 @@ class MidasParser(Parser):
         while not self.is_at_end() and not self.check(TokenType.RIGHT_BRACE):
             operations.append(self.op_declaration())
         self.consume(TokenType.RIGHT_BRACE, "Unclosed extend body")
-        location: Optional[Location] = None
-        if type.location:
-            location = keyword.location_to(self.previous())
+        location: Location = keyword.location_to(self.previous())
         return ExtendStmt(location=location, type=type, operations=operations)
 
     def op_declaration(self) -> OpStmt:

midas/parser/python.py

@@ -53,6 +53,7 @@ class PythonParser:
         return statements
 
     def parse_stmt(self, node: ast.stmt) -> None | Stmt | list[Stmt]:
+        location: Location = Location.from_ast(node)
         match node:
             case ast.AnnAssign():
                 return self.parse_annotation_assign(node)
@@ -64,7 +65,10 @@ class PythonParser:
                 return self.parse_function(node)
 
             case ast.Expr(value=expr):
-                return ExpressionStmt(expr=self.parse_expr(expr))
+                return ExpressionStmt(
+                    location=location,
+                    expr=self.parse_expr(expr),
+                )
 
             case _:
                 print(f"Unsupported statement: {ast.unparse(node)}")
@@ -128,11 +132,19 @@ class PythonParser:
                     kwonlyargs=kwonlyargs,
                 ),
                 returns=returns,
+                body=raw_body,
             ):
 
                 def parse_args(args_list: list[ast.arg]) -> list[Function.Argument]:
                     return [self._parse_function_argument(arg) for arg in args_list]
 
+                body: list[Stmt] = []
+                for stmt in raw_body:
+                    stmts = self.parse_stmt(stmt)
+                    if isinstance(stmts, Stmt):
+                        body.append(stmts)
+                    elif stmts is not None:
+                        body.extend(stmts)
                 return Function(
                     location=loc,
                     name=name,
@@ -140,6 +152,7 @@ class PythonParser:
                     args=parse_args(args),
                     kwonlyargs=parse_args(kwonlyargs),
                     returns=self._parse_type(returns) if returns is not None else None,
+                    body=body,
                 )
             case _:
                 print(f"Unsupported function definition: {ast.unparse(node)}")
@@ -257,12 +270,14 @@ class PythonParser:
                 raise UnsupportedSyntaxError(column)
 
     def parse_expr(self, node: ast.expr) -> Expr:
+        location: Location = Location.from_ast(node)
         match node:
             case ast.BoolOp():
                 return self.parse_bool_op(node)
 
             case ast.BinOp(left=left, op=op, right=right):
                 return BinaryExpr(
+                    location=location,
                     left=self.parse_expr(left),
                     operator=op,
                     right=self.parse_expr(right),
@@ -270,6 +285,7 @@ class PythonParser:
 
             case ast.UnaryOp(op=op, operand=right):
                 return UnaryExpr(
+                    location=location,
                     operator=op,
                     right=self.parse_expr(right),
                 )
@@ -281,33 +297,39 @@ class PythonParser:
                 return self.parse_call(node)
 
             case ast.Constant(value=value):
-                return LiteralExpr(value=value)
+                return LiteralExpr(location=location, value=value)
 
             case ast.Attribute(value=object, attr=name):
                 return GetExpr(
+                    location=location,
                     object=self.parse_expr(object),
                     name=name,
                 )
 
             case ast.Name(id=name):
-                return VariableExpr(name=name)
+                return VariableExpr(location=location, name=name)
 
             case _:
                 raise UnsupportedSyntaxError(node)
 
     def parse_bool_op(self, node: ast.BoolOp) -> LogicalExpr:
         op: ast.boolop = node.op
-        values: list[ast.expr] = node.values
+        rights: list[Expr] = [self.parse_expr(expr) for expr in node.values]
         expr: LogicalExpr = LogicalExpr(
-            left=self.parse_expr(values[0]),
+            location=Location.span(
+                rights[0].location,
+                rights[1].location,
+            ),
+            left=rights[0],
             operator=op,
-            right=self.parse_expr(values[1]),
+            right=rights[1],
         )
-        for value in values[2:]:
+        for right in rights[2:]:
             expr = LogicalExpr(
+                location=Location.span(expr.location, right.location),
                 left=expr,
                 operator=op,
-                right=self.parse_expr(value),
+                right=right,
             )
         return expr
 
@@ -315,24 +337,32 @@ class PythonParser:
         ops: list[ast.cmpop] = node.ops
         rights: list[Expr] = [self.parse_expr(expr) for expr in node.comparators]
         expr: Expr = CompareExpr(
+            location=Location.span(
+                rights[0].location,
+                rights[1].location,
+            ),
             left=self.parse_expr(node.left),
             operator=ops[0],
             right=rights[0],
         )
         for i, right in enumerate(rights[1:]):
+            comparison = CompareExpr(
+                location=Location.span(rights[i].location, right.location),
+                left=rights[i],
+                operator=ops[i],
+                right=right,
+            )
             expr = LogicalExpr(
+                location=Location.span(expr.location, comparison.location),
                 left=expr,
                 operator=ast.And(),
-                right=CompareExpr(
-                    left=rights[i],
-                    operator=ops[i],
-                    right=right,
-                ),
+                right=comparison,
             )
         return expr
 
     def parse_call(self, node: ast.Call) -> CallExpr:
         return CallExpr(
+            location=Location.from_ast(node),
             callee=self.parse_expr(node.func),
             arguments=[self.parse_expr(arg) for arg in node.args],
             keywords={

midas/resolver/midas.py

@@ -0,0 +1,113 @@
+from typing import Optional
+
+import midas.ast.midas as m
+from midas.checker.types import BaseType, SimpleType, Type
+
+
+class MidasResolver(m.Stmt.Visitor[None], m.Expr.Visitor[Type]):
+    def __init__(self) -> None:
+        self._types: dict[str, Type] = {}
+        self._operations: dict[tuple[Type, str, Type], Type] = {}
+
+        self._define_builtin()
+
+    def get_type(self, name: str) -> Type:
+        type: Optional[Type] = self._types.get(name)
+        if type is None:
+            raise NameError(f"Undefined type {name}")
+        return type
+
+    def get_operation_result(
+        self, left: Type, operator: str, right: Type
+    ) -> Optional[Type]:
+        operation: tuple[Type, str, Type] = (left, operator, right)
+        result: Optional[Type] = self._operations.get(operation)
+        return result
+
+    def _define_builtin(self):
+        self.define_type("bool", BaseType(name="bool"))
+        self.define_type("int", BaseType(name="int"))
+        self.define_type("float", BaseType(name="float"))
+        self.define_type("str", BaseType(name="str"))
+        self.define_operation(
+            left=self.get_type("int"),
+            operator="__add__",
+            right=self.get_type("int"),
+            result=self.get_type("int"),
+        )
+
+    def define_type(self, name: str, type: Type) -> Type:
+        if name in self._types:
+            raise ValueError(f"Type {name} already defined")
+        self._types[name] = type
+        return type
+
+    def define_operation(self, left: Type, operator: str, right: Type, result: Type):
+        operation: tuple[Type, str, Type] = (left, operator, right)
+        if operation in self._operations:
+            raise ValueError(
+                f"Operation {operator} already defined between {left} and {right}"
+            )
+        self._operations[operation] = result
+
+    def resolve(self, stmts: list[m.Stmt]):
+        for stmt in stmts:
+            stmt.accept(self)
+
+    def visit_simple_type_stmt(self, stmt: m.SimpleTypeStmt) -> None:
+        # TODO generics, optional, constraint
+        base: Type = self.get_type(stmt.base.name.lexeme)
+        match base:
+            case BaseType() | SimpleType():
+                type = SimpleType(
+                    name=stmt.name.lexeme,
+                    base=base,
+                )
+                self.define_type(type.name, type)
+            case _:
+                raise TypeError(f"Invalid base {base} for simple type")
+
+    def visit_complex_type_stmt(self, stmt: m.ComplexTypeStmt) -> None: ...
+
+    def visit_property_stmt(self, stmt: m.PropertyStmt) -> None: ...
+
+    def visit_extend_stmt(self, stmt: m.ExtendStmt) -> None:
+        base: Type = stmt.type.accept(self)
+        for op in stmt.operations:
+            right: Type = op.operand.accept(self)
+            result: Type = op.result.accept(self)
+            self.define_operation(
+                left=base,
+                operator=op.name.lexeme,
+                right=right,
+                result=result,
+            )
+
+    def visit_op_stmt(self, stmt: m.OpStmt) -> None: ...
+
+    def visit_predicate_stmt(self, stmt: m.PredicateStmt) -> None: ...
+
+    def visit_simple_type_expr(self, expr: m.SimpleTypeExpr) -> Type:
+        return self.get_type(expr.name.lexeme)
+
+    def visit_logical_expr(self, expr: m.LogicalExpr) -> Type: ...
+
+    def visit_binary_expr(self, expr: m.BinaryExpr) -> Type: ...
+
+    def visit_unary_expr(self, expr: m.UnaryExpr) -> Type: ...
+
+    def visit_get_expr(self, expr: m.GetExpr) -> Type: ...
+
+    def visit_variable_expr(self, expr: m.VariableExpr) -> Type: ...
+
+    def visit_grouping_expr(self, expr: m.GroupingExpr) -> Type:
+        return expr.expr.accept(self)
+
+    def visit_literal_expr(self, expr: m.LiteralExpr) -> Type: ...
+
+    def visit_wildcard_expr(self, expr: m.WildcardExpr) -> Type: ...
+
+    def visit_template_expr(self, expr: m.TemplateExpr) -> Type: ...
+
+    def visit_type_expr(self, expr: m.TypeExpr) -> Type:
+        return self.get_type(expr.name.lexeme)

midas/resolver/resolver.py

@@ -0,0 +1,112 @@
+import midas.ast.python as p
+
+
+class ResolverError(Exception): ...
+
+
+class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
+    def __init__(self):
+        self.locals: dict[p.Expr, int] = {}
+        self.scopes: list[dict[str, bool]] = []
+
+    def resolve(self, *objects: p.Stmt | p.Expr) -> None:
+        for obj in objects:
+            obj.accept(self)
+
+    def begin_scope(self):
+        self.scopes.append({})
+
+    def end_scope(self):
+        self.scopes.pop()
+
+    def declare(self, name: str) -> None:
+        if len(self.scopes) == 0:
+            return
+        scope: dict[str, bool] = self.scopes[-1]
+        if name in scope:
+            raise ResolverError(
+                f"A variable with the name {name} is already declared in this scope"
+            )
+        scope[name] = False
+
+    def define(self, name: str) -> None:
+        if len(self.scopes) == 0:
+            return
+        self.scopes[-1][name] = True
+
+    def resolve_local(self, expr: p.Expr, name: str) -> None:
+        for i, scope in enumerate(reversed(self.scopes)):
+            if name in scope:
+                self.locals[expr] = i
+                return
+
+    def resolve_function(self, function: p.Function) -> None:
+        self.begin_scope()
+        for param in function.all_args:
+            self.declare(param.name)
+            self.define(param.name)
+        self.resolve(*function.body)
+        self.end_scope()
+
+    def visit_expression_stmt(self, stmt: p.ExpressionStmt) -> None:
+        stmt.expr.accept(self)
+
+    def visit_function(self, stmt: p.Function) -> None:
+        # Declare before resolving body to allow recursion
+        self.declare(stmt.name)
+        self.define(stmt.name)
+        self.resolve_function(stmt)
+
+    def visit_type_assign(self, stmt: p.TypeAssign) -> None:
+        self.declare(stmt.name)
+        # NOTE: resolve type here?
+        self.define(stmt.name)
+
+    def visit_assign_stmt(self, stmt: p.AssignStmt) -> None:
+        self.resolve(stmt.value)
+        for target in stmt.targets:
+            match target:
+                case p.VariableExpr(name=name):
+                    self.resolve_local(target, name)
+                    # TODO: declare if not found
+                case _:
+                    raise Exception(f"Unsupported assignment to {target}")
+
+    def visit_binary_expr(self, expr: p.BinaryExpr) -> None:
+        self.resolve(expr.left)
+        self.resolve(expr.right)
+
+    def visit_compare_expr(self, expr: p.CompareExpr) -> None:
+        self.resolve(expr.left)
+        self.resolve(expr.right)
+
+    def visit_unary_expr(self, expr: p.UnaryExpr) -> None:
+        self.resolve(expr.right)
+
+    def visit_call_expr(self, expr: p.CallExpr) -> None:
+        self.resolve(expr.callee)
+        for arg in expr.arguments:
+            self.resolve(arg)
+        for arg in expr.keywords.values():
+            self.resolve(arg)
+
+    def visit_get_expr(self, expr: p.GetExpr) -> None:
+        self.resolve(expr.object)
+
+    def visit_literal_expr(self, expr: p.LiteralExpr) -> None:
+        pass
+
+    def visit_variable_expr(self, expr: p.VariableExpr) -> None:
+        if len(self.scopes) != 0 and self.scopes[-1].get(expr.name) is False:
+            raise ResolverError(
+                f"Cannot use local variable '{expr.name}' in its own initializer"
+            )  # aka. UnboundLocalError
+        self.resolve_local(expr, expr.name)
+
+    def visit_logical_expr(self, expr: p.LogicalExpr) -> None:
+        self.resolve(expr.left)
+        self.resolve(expr.right)
+
+    def visit_set_expr(self, expr: p.SetExpr) -> None:
+        self.resolve(expr.value)
+        self.resolve(expr.object)