feat(resolver): handle generic application

midas/checker/checker.py

@@ -6,19 +6,17 @@ 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.builtins import BUILTIN_SUBTYPES
 from midas.checker.diagnostic import Diagnostic, DiagnosticType
 from midas.checker.environment import Environment
 from midas.checker.operators import COMPARATOR_METHODS, OPERATOR_METHODS
 from midas.checker.types import (
-    AliasType,
-    BaseType,
     ComplexType,
     Function,
     Operation,
     Type,
     UnitType,
     UnknownType,
+    unfold_type,
 )
 from midas.lexer.midas import MidasLexer
 from midas.lexer.token import Token
@@ -178,157 +176,8 @@ class Checker(
         stmts: list[m.Stmt] = parser.parse()
         self.ctx.resolve(stmts)
 
-    def unfold_type(self, type: Type) -> Type:
-        match type:
-            case AliasType(type=ref_type):
-                return self.unfold_type(ref_type)
-            case _:
-                return type
-
     def is_subtype(self, type1: Type, type2: Type) -> bool:
-        """Check whether `type1` is a subtype of `type2`
+        return self.ctx.is_subtype(type1, type2)
-
-        For more details on the rules checked here, see TAPL Chap. 15-16-17
-
-        Args:
-            type1 (Type): the potential subtype
-            type2 (Type): the potential supertype
-
-        Returns:
-            bool: whether `type1` is a subtype of `type2`
-        """
-
-        if type1 == type2:
-            return True
-
-        match (type1, type2):
-            case (AliasType(type=base1), _):
-                return self.is_subtype(base1, type2)
-
-            case (BaseType(name=name1), BaseType(name=name2)):
-                return name1 in BUILTIN_SUBTYPES.get(name2, set())
-
-            case (ComplexType(properties=props1), ComplexType(properties=props2)):
-                for k, t in props2.items():
-                    if k not in props1:
-                        return False
-                    if not self.is_subtype(props1[k], t):
-                        return False
-                return True
-
-            case (Function(returns=return1), Function(returns=return2)):
-                if not self.is_func_subtype(type1, type2):
-                    return False
-                if not self.is_subtype(return1, return2):
-                    return False
-                return True
-
-        return False
-
-    # 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
-
-        Args:
-            func1 (Function): the potential function subtype
-            func2 (Function): the potential function supertype
-
-        Returns:
-            bool: whether `func1` is a subtype of `func2`
-        """
-        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}
-
-        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}
-
-        def is_arg_subtype(sub: Function.Argument, sup: Function.Argument) -> 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:
-                continue
-            else:
-                return False
-            if not is_arg_subtype(arg2, arg1):
-                return False
-
-        for name, arg1 in kw1.items():
-            arg2: Function.Argument
-            if name in kw2:
-                arg2 = kw2[name]
-            elif name in mixed_by_name:
-                arg2 = mixed_by_name[name]
-            elif not arg1.required:
-                continue
-            else:
-                return False
-            if not is_arg_subtype(arg2, arg1):
-                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]
-
-            # No match in func2 and arg is required
-            if pos_arg2 is None and kw_arg2 is None and arg1.required:
-                return False
-
-            # Matching keyword argument
-            if kw_arg2 is not None and not is_arg_subtype(kw_arg2, arg1):
-                return False
-
-            # Matching positional argument
-            if pos_arg2 is not None and not is_arg_subtype(pos_arg2, arg1):
-                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:
-                continue
-            if arg2.pos >= len(pos1) and arg2.pos not in mixed_positions:
-                return False
-
-        for name, arg2 in kw2.items():
-            if not arg2.required:
-                continue
-            if name not in kw1 and name not in mixed_names:
-                return False
-
-        for arg2 in mixed2:
-            if arg2.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
-            if not pos_match or not kw_match:
-                return False
-
-        return True
 
     def visit_expression_stmt(self, stmt: p.ExpressionStmt) -> None:
         self.type_of(stmt.expr)
@@ -470,7 +319,7 @@ class Checker(
 
     def _assign_attr(self, location: Location, target: p.GetExpr, value_type: Type):
         object: Type = self.type_of(target.object)
-        base_object: Type = self.unfold_type(object)
+        base_object: Type = unfold_type(object)
         match base_object:
             case ComplexType(properties=properties):
                 if target.name not in properties:
@@ -611,7 +460,7 @@ class Checker(
 
     def visit_get_expr(self, expr: p.GetExpr) -> Type:
         object: Type = self.type_of(expr.object)
-        base_object: Type = self.unfold_type(object)
+        base_object: Type = unfold_type(object)
         match base_object:
             case ComplexType(properties=properties):
                 if expr.name not in properties:

midas/checker/types.py

@@ -1,6 +1,7 @@
 from __future__ import annotations
 
 from dataclasses import dataclass
+from typing import Optional
 
 
 @dataclass(frozen=True, kw_only=True)
@@ -57,4 +58,83 @@ class Operation:
         right: Type
 
 
-Type = BaseType | AliasType | UnknownType | UnitType | Function | ComplexType
+@dataclass(frozen=True, kw_only=True)
+class TypeVar:
+    name: str
+    bound: Optional[Type]
+
+
+@dataclass(frozen=True, kw_only=True)
+class GenericType:
+    params: list[TypeVar]
+    body: Type
+
+
+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,
+        )
+
+    match type:
+        case BaseType(name=name) if name in substitutions:
+            return substitutions[name]
+
+        case AliasType(name=name, type=type2):
+            return AliasType(name=name, type=substitute_typevars(type2, substitutions))
+
+        case Function(
+            name=name,
+            pos_args=pos_args,
+            args=args,
+            kw_args=kw_args,
+            returns=returns,
+        ):
+            return Function(
+                name=name,
+                pos_args=list(map(sub_argument, pos_args)),
+                args=list(map(sub_argument, args)),
+                kw_args=list(map(sub_argument, kw_args)),
+                returns=substitute_typevars(returns, substitutions),
+            )
+
+        case ComplexType(properties=properties):
+            properties2: dict[str, Type] = {
+                name: substitute_typevars(prop, substitutions)
+                for name, prop in properties.items()
+            }
+            return ComplexType(properties=properties2)
+
+        case TypeVar(name=name):
+            if name in substitutions:
+                return substitutions[name]
+            raise ValueError(f"Missing TypeVar substitution for {name}")
+
+        case UnknownType() | UnitType():
+            return type
+
+        case _:
+            raise NotImplementedError(f"Unsupported type {type}")
+
+
+def unfold_type(type: Type) -> Type:
+    match type:
+        case AliasType(type=ref_type):
+            return unfold_type(ref_type)
+        case _:
+            return type
+
+
+Type = (
+    BaseType
+    | AliasType
+    | UnknownType
+    | UnitType
+    | Function
+    | ComplexType
+    | TypeVar
+    | GenericType
+)

midas/resolver/midas.py

@@ -1,12 +1,18 @@
 from typing import Optional
 
 import midas.ast.midas as m
+from midas.checker.builtins import BUILTIN_SUBTYPES
 from midas.checker.types import (
     AliasType,
+    BaseType,
     ComplexType,
+    Function,
+    GenericType,
     Operation,
     Type,
+    TypeVar,
     UnknownType,
+    substitute_typevars,
 )
 from midas.resolver.builtin import define_builtins
 
@@ -18,6 +24,8 @@ class MidasResolver(m.Stmt.Visitor[None], m.Expr.Visitor[None], m.Type.Visitor[T
         self._types: dict[str, Type] = {}
         self._operations: dict[Operation.CallSignature, Type] = {}
 
+        self._local_variables: dict[str, TypeVar] = {}
+
         define_builtins(self)
 
     def get_type(self, name: str) -> Type:
@@ -32,10 +40,11 @@ class MidasResolver(m.Stmt.Visitor[None], m.Expr.Visitor[None], m.Type.Visitor[T
         Returns:
             Type: the type
         """
-        type: Optional[Type] = self._types.get(name)
+        if name in self._local_variables:
-        if type is None:
+            return self._local_variables[name]
-            raise NameError(f"Undefined type {name}")
+        if name in self._types:
-        return type
+            return self._types[name]
+        raise NameError(f"Undefined type {name}")
 
     def get_operation_result(
         self, left: Type, operator: str, right: Type
@@ -121,12 +130,21 @@ class MidasResolver(m.Stmt.Visitor[None], m.Expr.Visitor[None], m.Type.Visitor[T
             stmt.accept(self)
 
     def visit_type_stmt(self, stmt: m.TypeStmt) -> None:
-        type: Type = stmt.type.accept(self)
+        params: list[TypeVar] = []
         for param in stmt.params:
+            name: str = param.name.lexeme
+            bound: Optional[Type] = None
             if param.bound is not None:
-                param.bound.accept(self)
+                bound = param.bound.accept(self)
+            var = TypeVar(name=name, bound=bound)
+            self._local_variables[name] = var
+            params.append(var)
+        type: Type = stmt.type.accept(self)
+        if len(params) != 0:
+            type = GenericType(params=params, body=type)
         name: str = stmt.name.lexeme
         self.define_type(name, AliasType(name=name, type=type))
+        self._local_variables.clear()
 
     def visit_property_stmt(self, stmt: m.PropertyStmt) -> None: ...
 
@@ -169,8 +187,36 @@ class MidasResolver(m.Stmt.Visitor[None], m.Expr.Visitor[None], m.Type.Visitor[T
     def visit_generic_type(self, type: m.GenericType) -> Type:
         type_: Type = type.type.accept(self)
         params: list[Type] = [param.accept(self) for param in type.params]
-        # TODO
+        return self.apply_generic(type_, params)
-        return UnknownType()
+
+    def apply_generic(self, type: Type, params: list[Type]) -> Type:
+        match type:
+            case AliasType(name=name, type=base):
+                return AliasType(name=name, type=self.apply_generic(base, params))
+
+            case GenericType(params=type_vars, body=body):
+                n_params: int = len(params)
+                n_type_vars: int = len(type_vars)
+                if n_params < n_type_vars:
+                    raise ValueError(
+                        f"Missing type parameters, expected {n_type_vars} but only {n_params} provided"
+                    )
+                if n_params > n_type_vars:
+                    raise ValueError(
+                        f"Too many type parameters, expected {n_type_vars} but {n_params} provided"
+                    )
+                substitutions: dict[str, Type] = {}
+                for param, type_var in zip(params, type_vars):
+                    if type_var.bound is not None and not self.is_subtype(
+                        param, type_var.bound
+                    ):
+                        raise ValueError(
+                            f"Type parameter {param} is not a subtype of {type_var.bound}"
+                        )
+                    substitutions[type_var.name] = param
+                return substitute_typevars(body, substitutions)
+            case _:
+                raise ValueError(f"{type} is not a generic type")
 
     def visit_constraint_type(self, type: m.ConstraintType) -> Type:
         type_: Type = type.type.accept(self)
@@ -184,3 +230,144 @@ class MidasResolver(m.Stmt.Visitor[None], m.Expr.Visitor[None], m.Type.Visitor[T
                 prop.name.lexeme: prop.type.accept(self) for prop in type.properties
             }
         )
+
+    def is_subtype(self, type1: Type, type2: Type) -> bool:
+        """Check whether `type1` is a subtype of `type2`
+
+        For more details on the rules checked here, see TAPL Chap. 15-16-17
+
+        Args:
+            type1 (Type): the potential subtype
+            type2 (Type): the potential supertype
+
+        Returns:
+            bool: whether `type1` is a subtype of `type2`
+        """
+
+        if type1 == type2:
+            return True
+
+        match (type1, type2):
+            case (AliasType(type=base1), _):
+                return self.is_subtype(base1, type2)
+
+            case (BaseType(name=name1), BaseType(name=name2)):
+                return name1 in BUILTIN_SUBTYPES.get(name2, set())
+
+            case (ComplexType(properties=props1), ComplexType(properties=props2)):
+                for k, t in props2.items():
+                    if k not in props1:
+                        return False
+                    if not self.is_subtype(props1[k], t):
+                        return False
+                return True
+
+            case (Function(), Function()):
+                return self.is_func_subtype(type1, type2)
+
+        return False
+
+    # 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
+
+        Args:
+            func1 (Function): the potential function subtype
+            func2 (Function): the potential function supertype
+
+        Returns:
+            bool: whether `func1` is a subtype of `func2`
+        """
+        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}
+
+        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}
+
+        def is_arg_subtype(sub: Function.Argument, sup: Function.Argument) -> 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:
+                continue
+            else:
+                return False
+            if not is_arg_subtype(arg2, arg1):
+                return False
+
+        for name, arg1 in kw1.items():
+            arg2: Function.Argument
+            if name in kw2:
+                arg2 = kw2[name]
+            elif name in mixed_by_name:
+                arg2 = mixed_by_name[name]
+            elif not arg1.required:
+                continue
+            else:
+                return False
+            if not is_arg_subtype(arg2, arg1):
+                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]
+
+            # No match in func2 and arg is required
+            if pos_arg2 is None and kw_arg2 is None and arg1.required:
+                return False
+
+            # Matching keyword argument
+            if kw_arg2 is not None and not is_arg_subtype(kw_arg2, arg1):
+                return False
+
+            # Matching positional argument
+            if pos_arg2 is not None and not is_arg_subtype(pos_arg2, arg1):
+                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:
+                continue
+            if arg2.pos >= len(pos1) and arg2.pos not in mixed_positions:
+                return False
+
+        for name, arg2 in kw2.items():
+            if not arg2.required:
+                continue
+            if name not in kw1 and name not in mixed_names:
+                return False
+
+        for arg2 in mixed2:
+            if arg2.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
+            if not pos_match or not kw_match:
+                return False
+
+        return True