feat(checker): handle assignments to attributes

add type judgements to checker test results and update all tests (including the new subtyping rules)

examples/01_simple_type_checking/04_complex_types.midas

@@ -0,0 +1,11 @@
+type Meter = float
+
+extend Meter {
+    op __add__(Meter) -> Meter
+    op __sub__(Meter) -> Meter
+}
+
+type Coordinate = {
+    x: Meter
+    y: Meter
+}

examples/01_simple_type_checking/04_complex_types.py

@@ -0,0 +1,11 @@
+# type: ignore
+# ruff: disable [F821]
+p1: Coordinate
+p2: Coordinate
+
+diff_x = p2.x - p1.x
+diff_y = p2.y - p1.y
+
+dist = diff_x + diff_y
+
+p2.x += cast(Meter, 1)

gen/python.py

@@ -128,12 +128,6 @@ class LogicalExpr:
     right: Expr
 
 
-class SetExpr:
-    object: Expr
-    name: str
-    value: Expr
-
-
 class CastExpr:
     type: MidasType
     expr: Expr

midas/ast/printer.py

@@ -602,17 +602,6 @@ class PythonAstPrinter(
             with self._child_level(single=True):
                 expr.right.accept(self)
 
-    def visit_set_expr(self, expr: p.SetExpr) -> None:
-        self._write_line("SetExpr")
-        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}")
-            self._write_line("value", last=True)
-            with self._child_level(single=True):
-                expr.value.accept(self)
-
     def visit_cast_expr(self, expr: p.CastExpr) -> None:
         self._write_line("CastExpr")
         with self._child_level():

midas/ast/python.py

@@ -214,9 +214,6 @@ class Expr(ABC):
         @abstractmethod
         def visit_logical_expr(self, expr: LogicalExpr) -> T: ...
 
-        @abstractmethod
-        def visit_set_expr(self, expr: SetExpr) -> T: ...
-
         @abstractmethod
         def visit_cast_expr(self, expr: CastExpr) -> T: ...
 
@@ -298,16 +295,6 @@ class LogicalExpr(Expr):
         return visitor.visit_logical_expr(self)
 
 
-@dataclass(frozen=True)
-class SetExpr(Expr):
-    object: Expr
-    name: str
-    value: Expr
-
-    def accept(self, visitor: Expr.Visitor[T]) -> T:
-        return visitor.visit_set_expr(self)
-
-
 @dataclass(frozen=True)
 class CastExpr(Expr):
     type: MidasType

midas/checker/builtins.py

@@ -0,0 +1,4 @@
+BUILTIN_SUBTYPES: dict[str, set[str]] = {
+    "float": {"int"},
+    "int": {"bool"},
+}

midas/checker/checker.py

@@ -6,10 +6,20 @@ 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 Function, Type, UnitType, UnknownType
+from midas.checker.types import (
+    AliasType,
+    BaseType,
+    ComplexType,
+    Function,
+    Operation,
+    Type,
+    UnitType,
+    UnknownType,
+)
 from midas.lexer.midas import MidasLexer
 from midas.lexer.token import Token
 from midas.parser.midas import MidasParser
@@ -48,6 +58,7 @@ class Checker(
         self.env: Environment = self.global_env
         self.locals: dict[p.Expr, int] = locals
         self.diagnostics: list[Diagnostic] = []
+        self.judgements: list[tuple[p.Expr, Type]] = []
 
     def diagnostic(self, type: DiagnosticType, location: Location, message: str):
         self.diagnostics.append(
@@ -89,7 +100,9 @@ class Checker(
         Returns:
             Type: the type of the given expression
         """
-        return expr.accept(self)
+        type: Type = expr.accept(self)
+        self.judgements.append((expr, type))
+        return type
 
     def process_block(self, block: list[p.Stmt], env: Environment) -> bool:
         """Evaluate a sequence of statements
@@ -165,6 +178,158 @@ 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`
+
+        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)
 
@@ -181,30 +346,37 @@ class Checker(
                 return arg.default.accept(self)
             return UnknownType()
 
+        pos: int = 0
         for arg in stmt.posonlyargs:
             pos_args.append(
                 Function.Argument(
+                    pos=pos,
                     name=arg.name,
                     type=eval_arg_type(arg),
                     required=arg.default is None,
                 )
             )
+            pos += 1
         for arg in stmt.args:
             args.append(
                 Function.Argument(
+                    pos=pos,
                     name=arg.name,
                     type=eval_arg_type(arg),
                     required=arg.default is None,
                 )
             )
+            pos += 1
         for arg in stmt.kwonlyargs:
             kw_args.append(
                 Function.Argument(
+                    pos=pos,  # not relevant
                     name=arg.name,
                     type=eval_arg_type(arg),
                     required=arg.default is None,
                 )
             )
+            pos += 1
 
         for arg in pos_args + args + kw_args:
             env.define(arg.name, arg.type)
@@ -263,23 +435,65 @@ class Checker(
         self.env.define(stmt.name, type)
 
     def visit_assign_stmt(self, stmt: p.AssignStmt) -> None:
-        value: Type = self.type_of(stmt.value)
+        value_type: Type = self.type_of(stmt.value)
         for target in stmt.targets:
+            self._assign(stmt.location, target, value_type)
+
+    def _assign(self, location: Location, target: p.Expr, value_type: Type):
+        match target:
+            case p.VariableExpr():
+                self._assign_var(location, target, value_type)
+
+            case p.GetExpr():
+                self._assign_attr(location, target, value_type)
+
+            case _:
                 if not isinstance(target, p.VariableExpr):
                     self.logger.warning(f"Unsupported assignment to {target}")
                     self.warning(target.location, f"Unsupported assignment to {target}")
-                continue
+
+    def _assign_var(self, location: Location, target: p.VariableExpr, value_type: Type):
         name: str = target.name
         var_type: Optional[Type] = self.look_up_variable(name, target)
 
         if var_type is None:
-                self.env.define(name, value)
+            self.env.define(name, value_type)
         else:
-                # TODO: implement real comparison method
+            # S <: T
-                if var_type != value:
+            # Γ, x: T   v: S
+            # x = v
+            if not self.is_subtype(value_type, var_type):
                 self.error(
-                        stmt.location,
+                    location,
-                        f"Cannot assign {value} to {name} of type {var_type}",
+                    f"Cannot assign {value_type} to {name} of type {var_type}",
+                )
+
+    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)
+        match base_object:
+            case ComplexType(properties=properties):
+                if target.name not in properties:
+                    self.error(
+                        target.location, f"Unknown property '{target.name} on {object}"
+                    )
+                    return
+
+                prop_type: Type = properties[target.name]
+                if not self.is_subtype(value_type, prop_type):
+                    self.error(
+                        location,
+                        f"Cannot assign {value_type} to property '{target.name}' of type {prop_type} on {object}",
+                    )
+                    return
+
+            case UnknownType():
+                pass
+
+            case _:
+                self.error(
+                    target.location,
+                    f"Cannot assign {value_type} to unknown property '{target.name}' on {object}",
                 )
 
     def visit_return_stmt(self, stmt: p.ReturnStmt) -> None:
@@ -317,14 +531,48 @@ class Checker(
         left: Type = self.type_of(expr.left)
         right: Type = self.type_of(expr.right)
 
-        result: Optional[Type] = self.ctx.get_operation_result(left, method, right)
+        operations: list[Operation] = self.ctx.get_operations_by_name(method)
-        if result is None:
+        valid_operations: list[Operation] = []
+        for op in operations:
+            sig: Operation.CallSignature = op.signature
+            if self.is_subtype(left, sig.left) and self.is_subtype(right, sig.right):
+                valid_operations.append(op)
+
+        if len(valid_operations) == 0:
             self.error(
                 expr.location,
                 f"Undefined operation {method} between {left} and {right}",
             )
             return UnknownType()
-        return result
+        elif len(valid_operations) == 1:
+            self.logger.debug(f"Unique operation {method} between {left} and {right}")
+            return valid_operations[0].result
+
+        for i, op1 in enumerate(valid_operations):
+            sig1: Operation.CallSignature = op1.signature
+            best_match: bool = True
+            for j, op2 in enumerate(valid_operations):
+                if i == j:
+                    continue
+                sig2: Operation.CallSignature = op2.signature
+                if not self.is_subtype(sig1.left, sig2.left) or not self.is_subtype(
+                    sig1.right, sig2.right
+                ):
+                    best_match = False
+                    break
+                self.logger.debug(f"{op1} is a full overload of {op2}")
+            if best_match:
+                return op1.result
+
+        overloads: list[str] = [
+            f"({op.signature.left} {op.signature.method} {op.signature.right}) -> {op.result}"
+            for op in valid_operations
+        ]
+        self.error(
+            expr.location,
+            f"Ambiguous operation {method} between {left} and {right}, multiple matching overloads: {', '.join(overloads)}",
+        )
+        return UnknownType()
 
     def visit_compare_expr(self, expr: p.CompareExpr) -> Type:
         method: Optional[str] = COMPARATOR_METHODS.get(expr.operator.__class__)
@@ -354,14 +602,33 @@ class Checker(
         function: Function = callee
         mapped: list[MappedArgument] = self.map_call_arguments(function, expr)
         for arg in mapped:
-            if arg.type != arg.argument.type:
+            if not self.is_subtype(arg.type, arg.argument.type):
                 self.error(
                     arg.expr.location,
                     f"Wrong type for argument '{arg.argument.name}', expected {arg.argument.type}, got {arg.type}",
                 )
         return function.returns
 
-    def visit_get_expr(self, expr: p.GetExpr) -> Type: ...
+    def visit_get_expr(self, expr: p.GetExpr) -> Type:
+        object: Type = self.type_of(expr.object)
+        base_object: Type = self.unfold_type(object)
+        match base_object:
+            case ComplexType(properties=properties):
+                if expr.name not in properties:
+                    self.error(
+                        expr.location, f"Unknown property '{expr.name} on {object}"
+                    )
+                    return UnknownType()
+                return properties[expr.name]
+
+            case UnknownType():
+                return UnknownType()
+
+            case _:
+                self.error(
+                    expr.location, f"Cannot get property '{expr.name}' on {object}"
+                )
+                return UnknownType()
 
     def visit_literal_expr(self, expr: p.LiteralExpr) -> Type:
         match expr.value:
@@ -383,15 +650,17 @@ class Checker(
     def visit_logical_expr(self, expr: p.LogicalExpr) -> Type:
         left: Type = expr.left.accept(self)
         right: Type = expr.right.accept(self)
-        # TODO: union type
+
-        if left != right:
+        if self.is_subtype(left, right):
-            self.error(
+            return right
-                expr.location,
+        if self.is_subtype(right, left):
-                f"Operands must be of the same type, left={left} != right={right}",
-            )
             return left
 
-    def visit_set_expr(self, expr: p.SetExpr) -> Type: ...
+        self.error(
+            expr.location,
+            f"Incompatible operand types, {left=} and {right=}",
+        )
+        return UnknownType()
 
     def visit_cast_expr(self, expr: p.CastExpr) -> Type:
         return expr.type.accept(self)
@@ -407,13 +676,16 @@ class Checker(
 
         true_type: Type = expr.if_true.accept(self)
         false_type: Type = expr.if_false.accept(self)
-        if true_type != false_type:
+        if self.is_subtype(true_type, false_type):
+            return false_type
+        if self.is_subtype(false_type, true_type):
+            return true_type
+
         self.error(
             expr.location,
-                f"Type mismatch in ternary if branches: true={true_type} != false={false_type}",
+            f"Incompatible types in ternary if branches: true={true_type} and false={false_type}",
         )
         return UnknownType()
-        return true_type
 
     def visit_base_type(self, node: p.BaseType) -> Type:
         return self.ctx.get_type(node.base)

midas/checker/diagnostic.py

@@ -19,7 +19,8 @@ class Diagnostic:
     type: DiagnosticType
     message: str
 
-    def __str__(self) -> str:
+    @property
+    def location_str(self) -> str:
         start_loc: str = f"L{self.location.lineno}:{self.location.col_offset+1}"
         end_loc: Optional[str] = ""
         if (
@@ -30,4 +31,7 @@ class Diagnostic:
         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}"
+        return f"{self.type} in {self.file_path} {loc}"
+
+    def __str__(self) -> str:
+        return f"{self.location_str}: {self.message}"

midas/checker/types.py

@@ -34,6 +34,7 @@ class Function:
 
     @dataclass(frozen=True, kw_only=True)
     class Argument:
+        pos: int
         name: str
         type: Type
         required: bool
@@ -44,4 +45,16 @@ class ComplexType:
     properties: dict[str, Type]
 
 
+@dataclass(frozen=True, kw_only=True)
+class Operation:
+    signature: CallSignature
+    result: Type
+
+    @dataclass(frozen=True, kw_only=True)
+    class CallSignature:
+        left: Type
+        method: str
+        right: Type
+
+
 Type = BaseType | AliasType | UnknownType | UnitType | Function | ComplexType

midas/cli/ansi.py

@@ -0,0 +1,41 @@
+class Ansi:
+    CTRL = "\x1b["
+    RESET = CTRL + "0m"
+    BOLD = CTRL + "1m"
+    DIM = CTRL + "2m"
+    ITALIC = CTRL + "3m"
+    UNDERLINE = CTRL + "4m"
+
+    BLACK = 0
+    RED = 1
+    GREEN = 2
+    YELLOW = 3
+    BLUE = 4
+    MAGENTA = 5
+    CYAN = 6
+    WHITE = 7
+
+    BRIGHT_BLACK = 60
+    BRIGHT_RED = 61
+    BRIGHT_GREEN = 62
+    BRIGHT_YELLOW = 63
+    BRIGHT_BLUE = 64
+    BRIGHT_MAGENTA = 65
+    BRIGHT_CYAN = 66
+    BRIGHT_WHITE = 67
+
+    @classmethod
+    def FG(cls, col: int) -> str:
+        return f"{cls.CTRL}{30 + col}m"
+
+    @classmethod
+    def BG(cls, col: int) -> str:
+        return f"{cls.CTRL}{40 + col}m"
+
+    @classmethod
+    def FG_RGB(cls, r: int, g: int, b: int) -> str:
+        return f"{cls.CTRL}38;2;{r};{g};{b}m"
+
+    @classmethod
+    def BG_RGB(cls, r: int, g: int, b: int) -> str:
+        return f"{cls.CTRL}48;2;{r};{g};{b}m"

midas/cli/highlighter.py

@@ -210,8 +210,6 @@ class PythonHighlighter(
 
     def visit_logical_expr(self, expr: p.LogicalExpr) -> None: ...
 
-    def visit_set_expr(self, expr: p.SetExpr) -> None: ...
-
     def visit_cast_expr(self, expr: p.CastExpr) -> None: ...
 
     def visit_ternary_expr(self, expr: p.TernaryExpr) -> None: ...

midas/cli/main.py

@@ -8,10 +8,12 @@ import click
 
 import midas.ast.midas as m
 import midas.ast.python as p
+from midas.ast.location import Location
 from midas.ast.printer import MidasAstPrinter, MidasPrinter, PythonAstPrinter
 from midas.checker.checker import Checker
-from midas.checker.diagnostic import Diagnostic
+from midas.checker.diagnostic import Diagnostic, DiagnosticType
 from midas.checker.types import Type
+from midas.cli.ansi import Ansi
 from midas.cli.highlighter import (
     DiagnosticsHighlighter,
     Highlighter,
@@ -32,12 +34,69 @@ def midas():
     pass
 
 
+def print_diagnostic(lines: list[str], diagnostic: Diagnostic, indent: int = 4):
+    """Pretty-print a diagnostic, showing some context if possible
+
+    If the diagnostic concerns a specific part of one line, the line is shown
+    with the affected part highlighted. The message is clearly printed under the
+    line with an underline further indicating the target expression.
+
+    If multiple lines are concerned, no context is shown, only the
+    diagnostic type, location and message
+
+    Args:
+        lines (list[str]): source code lines
+        diagnostic (Diagnostic): the diagnostic to print
+        indent (int, optional): the number of spaces added before the target line to indent if from the location header. Defaults to 4.
+    """
+
+    loc: Location = diagnostic.location
+    if loc.lineno != loc.end_lineno:
+        print(diagnostic)
+        return
+
+    start_offset: int = loc.col_offset
+    end_offset: int = loc.end_col_offset or (start_offset + 1)
+
+    line: str = lines[loc.lineno - 1]
+    before: str = line[:start_offset]
+    after: str = line[end_offset:]
+
+    color: int = {
+        DiagnosticType.ERROR: Ansi.RED,
+        DiagnosticType.WARNING: Ansi.YELLOW,
+        DiagnosticType.INFO: Ansi.CYAN,
+    }.get(diagnostic.type, Ansi.WHITE)
+
+    subject: str = Ansi.FG(color) + line[start_offset:end_offset] + Ansi.RESET
+    cursor: str = (
+        " " * start_offset
+        + Ansi.FG(color)
+        + "~" * (end_offset - start_offset)
+        + "> "
+        + diagnostic.message
+        + Ansi.RESET
+    )
+
+    indent_str: str = " " * indent
+    print(diagnostic.location_str + ":")
+    print(indent_str + before + subject + after)
+    print(indent_str + cursor)
+    print()
+
+
 @midas.command()
 @click.option("-l", "--highlight", type=click.File("w"))
 @click.option("-t", "--types", type=click.File("r"), multiple=True)
+@click.option("-v", "--verbose", is_flag=True)
 @click.argument("file", type=click.File("r"))
-def compile(highlight: Optional[TextIO], file: TextIO, types: tuple[TextIO]):
+def compile(
-    logging.basicConfig(level=logging.DEBUG)
+    highlight: Optional[TextIO],
+    types: tuple[TextIO],
+    verbose: bool,
+    file: TextIO,
+):
+    logging.basicConfig(level=logging.DEBUG if verbose else logging.WARN)
     source: str = file.read()
     tree: ast.Module = ast.parse(source, filename=file.name)
     parser = PythonParser()
@@ -51,9 +110,11 @@ def compile(highlight: Optional[TextIO], file: TextIO, types: tuple[TextIO]):
         types_paths=types_paths,
     )
     diagnostics: list[Diagnostic] = checker.check(stmts)
+    lines: list[str] = source.split("\n")
     for diagnostic in diagnostics:
-        print(diagnostic)
+        print_diagnostic(lines, diagnostic)
 
+    if verbose:
         print(
             json.dumps(
                 UniversalJSONDumper.dump(

midas/resolver/midas.py

@@ -3,6 +3,8 @@ from typing import Optional
 import midas.ast.midas as m
 from midas.checker.types import (
     AliasType,
+    ComplexType,
+    Operation,
     Type,
     UnknownType,
 )
@@ -14,7 +16,7 @@ class MidasResolver(m.Stmt.Visitor[None], m.Expr.Visitor[None], m.Type.Visitor[T
 
     def __init__(self) -> None:
         self._types: dict[str, Type] = {}
-        self._operations: dict[tuple[Type, str, Type], Type] = {}
+        self._operations: dict[Operation.CallSignature, Type] = {}
 
         define_builtins(self)
 
@@ -48,10 +50,26 @@ class MidasResolver(m.Stmt.Visitor[None], m.Expr.Visitor[None], m.Type.Visitor[T
         Returns:
             Optional[Type]: the result type, or None if no matching operation was found
         """
-        operation: tuple[Type, str, Type] = (left, operator, right)
+        signature: Operation.CallSignature = Operation.CallSignature(
-        result: Optional[Type] = self._operations.get(operation)
+            left=left,
+            method=operator,
+            right=right,
+        )
+        result: Optional[Type] = self._operations.get(signature)
         return result
 
+    def get_operations_by_name(self, name: str) -> list[Operation]:
+        operations: list[Operation] = []
+        for signature, result in self._operations.items():
+            if signature.method == name:
+                operations.append(
+                    Operation(
+                        signature=signature,
+                        result=result,
+                    )
+                )
+        return operations
+
     def define_type(self, name: str, type: Type) -> Type:
         """Define a type in the registry
 
@@ -82,12 +100,16 @@ class MidasResolver(m.Stmt.Visitor[None], m.Expr.Visitor[None], m.Type.Visitor[T
         Raises:
             ValueError: if an operation is already defined with these operands and name
         """
-        operation: tuple[Type, str, Type] = (left, operator, right)
+        signature: Operation.CallSignature = Operation.CallSignature(
-        if operation in self._operations:
+            left=left,
+            method=operator,
+            right=right,
+        )
+        if signature in self._operations:
             raise ValueError(
                 f"Operation {operator} already defined between {left} and {right}"
             )
-        self._operations[operation] = result
+        self._operations[signature] = result
 
     def resolve(self, stmts: list[m.Stmt]):
         """Process a sequence of statements
@@ -157,7 +179,8 @@ class MidasResolver(m.Stmt.Visitor[None], m.Expr.Visitor[None], m.Type.Visitor[T
         return UnknownType()
 
     def visit_complex_type(self, type: m.ComplexType) -> Type:
-        for prop in type.properties:
+        return ComplexType(
-            prop.accept(self)
+            properties={
-        # TODO
+                prop.name.lexeme: prop.type.accept(self) for prop in type.properties
-        return UnknownType()
+            }
+        )

midas/resolver/resolver.py

@@ -111,9 +111,8 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
         self.resolve(stmt.value)
         for target in stmt.targets:
             match target:
-                case p.VariableExpr(name=name):
+                case p.VariableExpr() | p.GetExpr():
-                    self.resolve_local(target, name)
+                    target.accept(self)
-                    # TODO: declare if not found
                 case _:
                     raise Exception(f"Unsupported assignment to {target}")
 
@@ -174,10 +173,6 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[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)
-
     def visit_cast_expr(self, expr: p.CastExpr) -> None:
         self.resolve(expr.expr)
 

tests/base.py

@@ -29,7 +29,7 @@ class Tester(ABC):
     def _list_tests(self) -> list[Path]: ...
 
     def run_all_tests(self) -> bool:
-        paths: list[Path] = self._list_tests()
+        paths: list[Path] = sorted(self._list_tests())
         return self.run_tests(paths)
 
     def run_tests(self, tests: list[Path]) -> bool:
@@ -40,7 +40,7 @@ class Tester(ABC):
 
         print(rule)
         for i, test in enumerate(tests):
-            print(f"Case {i+1}/{n}: {test.relative_to(self.CASES_DIR)}")
+            print(f"Case {i+1}/{n}: {test.resolve().relative_to(self.CASES_DIR)}")
             success: bool = self._run_test(test)
             if success:
                 successes += 1
@@ -78,7 +78,7 @@ class Tester(ABC):
     def _exec_case(self, path: Path) -> CaseResult: ...
 
     def update_all_tests(self):
-        paths: list[Path] = self._list_tests()
+        paths: list[Path] = sorted(self._list_tests())
         return self.update_tests(paths)
 
     def update_tests(self, tests: list[Path]):

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

@@ -1,3 +1,4 @@
 {
-  "diagnostics": []
+  "diagnostics": [],
+  "judgments": []
 }

tests/cases/checker/02_simple_operations.py.ref.json

@@ -13,34 +13,167 @@
         ]
       },
       "message": "Cannot assign BaseType(name='str') to c of type BaseType(name='int')"
+    }
+  ],
+  "judgments": [
+    {
+      "location": {
+        "from": "L1:9",
+        "to": "L1:10"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 3
+      },
+      "type": {
+        "name": "int"
+      }
     },
     {
-      "type": "Error",
       "location": {
-        "start": [
+        "from": "L2:9",
-          9,
+        "to": "L2:10"
-          4
-        ],
-        "end": [
-          9,
-          9
-        ]
       },
-      "message": "Undefined operation __add__ between BaseType(name='bool') and BaseType(name='bool')"
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 4
+      },
+      "type": {
+        "name": "int"
+      }
     },
     {
-      "type": "Error",
       "location": {
-        "start": [
+        "from": "L4:4",
-          11,
+        "to": "L4:5"
-          0
-        ],
-        "end": [
-          11,
-          12
-        ]
       },
-      "message": "Cannot assign BaseType(name='int') to f of type BaseType(name='float')"
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "a"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L4:8",
+        "to": "L4:9"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "b"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L4:4",
+        "to": "L4:9"
+      },
+      "expr": {
+        "_type": "BinaryExpr",
+        "left": {
+          "_type": "VariableExpr",
+          "name": "a"
+        },
+        "operator": "+",
+        "right": {
+          "_type": "VariableExpr",
+          "name": "b"
+        }
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L6:4",
+        "to": "L6:13"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": "invalid"
+      },
+      "type": {
+        "name": "str"
+      }
+    },
+    {
+      "location": {
+        "from": "L8:4",
+        "to": "L8:8"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": true
+      },
+      "type": {
+        "name": "bool"
+      }
+    },
+    {
+      "location": {
+        "from": "L9:4",
+        "to": "L9:5"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "d"
+      },
+      "type": {
+        "name": "bool"
+      }
+    },
+    {
+      "location": {
+        "from": "L9:8",
+        "to": "L9:9"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "d"
+      },
+      "type": {
+        "name": "bool"
+      }
+    },
+    {
+      "location": {
+        "from": "L9:4",
+        "to": "L9:9"
+      },
+      "expr": {
+        "_type": "BinaryExpr",
+        "left": {
+          "_type": "VariableExpr",
+          "name": "d"
+        },
+        "operator": "+",
+        "right": {
+          "_type": "VariableExpr",
+          "name": "d"
+        }
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L11:11",
+        "to": "L11:12"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "a"
+      },
+      "type": {
+        "name": "int"
+      }
     }
   ]
 }

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

@@ -1,3 +1,109 @@
 {
-  "diagnostics": []
+  "diagnostics": [],
+  "judgments": [
+    {
+      "location": {
+        "from": "L4:18",
+        "to": "L4:37"
+      },
+      "expr": {
+        "_type": "CastExpr",
+        "type": {
+          "_type": "BaseType",
+          "base": "Meter",
+          "param": null
+        },
+        "expr": {
+          "_type": "LiteralExpr",
+          "value": 123.45
+        }
+      },
+      "type": {
+        "name": "Meter",
+        "type": {
+          "name": "float"
+        }
+      }
+    },
+    {
+      "location": {
+        "from": "L5:15",
+        "to": "L5:32"
+      },
+      "expr": {
+        "_type": "CastExpr",
+        "type": {
+          "_type": "BaseType",
+          "base": "Second",
+          "param": null
+        },
+        "expr": {
+          "_type": "LiteralExpr",
+          "value": 6.7
+        }
+      },
+      "type": {
+        "name": "Second",
+        "type": {
+          "name": "float"
+        }
+      }
+    },
+    {
+      "location": {
+        "from": "L6:8",
+        "to": "L6:16"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "distance"
+      },
+      "type": {
+        "name": "Meter",
+        "type": {
+          "name": "float"
+        }
+      }
+    },
+    {
+      "location": {
+        "from": "L6:19",
+        "to": "L6:23"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "time"
+      },
+      "type": {
+        "name": "Second",
+        "type": {
+          "name": "float"
+        }
+      }
+    },
+    {
+      "location": {
+        "from": "L6:8",
+        "to": "L6:23"
+      },
+      "expr": {
+        "_type": "BinaryExpr",
+        "left": {
+          "_type": "VariableExpr",
+          "name": "distance"
+        },
+        "operator": "/",
+        "right": {
+          "_type": "VariableExpr",
+          "name": "time"
+        }
+      },
+      "type": {
+        "name": "MeterPerSecond",
+        "type": {
+          "name": "float"
+        }
+      }
+    }
+  ]
 }

tests/cases/checker/05_control_flow.py.ref.json

@@ -42,5 +42,215 @@
       },
       "message": "Mixed return types: [BaseType(name='int'), BaseType(name='str')]"
     }
+  ],
+  "judgments": [
+    {
+      "location": {
+        "from": "L2:11",
+        "to": "L2:12"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "a"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L2:15",
+        "to": "L2:16"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "b"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L5:7",
+        "to": "L5:8"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "a"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L5:11",
+        "to": "L5:12"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "b"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L6:15",
+        "to": "L6:16"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "b"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L6:19",
+        "to": "L6:20"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "a"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L8:15",
+        "to": "L8:16"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "a"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L8:19",
+        "to": "L8:20"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "b"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L15:7",
+        "to": "L15:8"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "a"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L15:11",
+        "to": "L15:13"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 10
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L16:15",
+        "to": "L16:16"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "a"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L16:19",
+        "to": "L16:21"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 10
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L22:7",
+        "to": "L22:8"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "a"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L22:11",
+        "to": "L22:12"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "b"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L23:15",
+        "to": "L23:16"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "b"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L23:19",
+        "to": "L23:20"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "a"
+      },
+      "type": {
+        "name": "int"
+      }
+    }
   ]
 }

tests/cases/checker/06_subtyping.py

@@ -0,0 +1,12 @@
+v1: int = 3
+v2: float = 4
+
+
+def maximum(a: float, b: float):
+    if b > a:
+        return b
+    return a
+
+
+v3 = maximum(v1, v2)
+v3 = v1 + v2

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

@@ -0,0 +1,193 @@
+{
+  "diagnostics": [],
+  "judgments": [
+    {
+      "location": {
+        "from": "L1:10",
+        "to": "L1:11"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 3
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L2:12",
+        "to": "L2:13"
+      },
+      "expr": {
+        "_type": "LiteralExpr",
+        "value": 4
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L6:7",
+        "to": "L6:8"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "b"
+      },
+      "type": {
+        "name": "float"
+      }
+    },
+    {
+      "location": {
+        "from": "L6:11",
+        "to": "L6:12"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "a"
+      },
+      "type": {
+        "name": "float"
+      }
+    },
+    {
+      "location": {
+        "from": "L11:5",
+        "to": "L11:12"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "maximum"
+      },
+      "type": {
+        "name": "maximum",
+        "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",
+        "to": "L11:15"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "v1"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L11:17",
+        "to": "L11:19"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "v2"
+      },
+      "type": {
+        "name": "float"
+      }
+    },
+    {
+      "location": {
+        "from": "L11:5",
+        "to": "L11:20"
+      },
+      "expr": {
+        "_type": "CallExpr",
+        "callee": {
+          "_type": "VariableExpr",
+          "name": "maximum"
+        },
+        "arguments": [
+          {
+            "_type": "VariableExpr",
+            "name": "v1"
+          },
+          {
+            "_type": "VariableExpr",
+            "name": "v2"
+          }
+        ],
+        "keywords": {}
+      },
+      "type": {
+        "name": "float"
+      }
+    },
+    {
+      "location": {
+        "from": "L12:5",
+        "to": "L12:7"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "v1"
+      },
+      "type": {
+        "name": "int"
+      }
+    },
+    {
+      "location": {
+        "from": "L12:10",
+        "to": "L12:12"
+      },
+      "expr": {
+        "_type": "VariableExpr",
+        "name": "v2"
+      },
+      "type": {
+        "name": "float"
+      }
+    },
+    {
+      "location": {
+        "from": "L12:5",
+        "to": "L12:12"
+      },
+      "expr": {
+        "_type": "BinaryExpr",
+        "left": {
+          "_type": "VariableExpr",
+          "name": "v1"
+        },
+        "operator": "+",
+        "right": {
+          "_type": "VariableExpr",
+          "name": "v2"
+        }
+      },
+      "type": {
+        "name": "float"
+      }
+    }
+  ]
+}

tests/checker.py

@@ -6,14 +6,17 @@ from pathlib import Path
 import midas.ast.python as p
 from midas.checker.checker import Checker
 from midas.checker.diagnostic import Diagnostic
+from midas.checker.types import Type
 from midas.parser.python import PythonParser
 from midas.resolver.resolver import Resolver
 from tests.base import Tester
+from tests.serializer.python import PythonAstJsonSerializer
 
 
 @dataclass
 class CaseResult:
     diagnostics: list[dict] = field(default_factory=list)
+    judgments: list = field(default_factory=list)
 
     def dumps(self) -> str:
         return json.dumps(asdict(self), indent=2)
@@ -49,6 +52,7 @@ class CheckerTester(Tester):
             source_path=path,
             types_paths=types_paths,
         )
+
         diagnostics: list[Diagnostic] = checker.check(stmts)
         for diagnostic in diagnostics:
             result.diagnostics.append(
@@ -68,6 +72,21 @@ class CheckerTester(Tester):
                 }
             )
 
+        judgements: list[tuple[p.Expr, Type]] = checker.judgements
+        serializer = PythonAstJsonSerializer()
+        for expr, type in judgements:
+            loc = expr.location
+            result.judgments.append(
+                {
+                    "location": {
+                        "from": f"L{loc.lineno}:{loc.col_offset}",
+                        "to": f"L{loc.end_lineno}:{loc.end_col_offset}",
+                    },
+                    "expr": expr.accept(serializer),
+                    "type": asdict(type),
+                }
+            )
+
         return result
 
 

tests/serializer/python.py

@@ -20,7 +20,6 @@ from midas.ast.python import (
     LogicalExpr,
     MidasType,
     ReturnStmt,
-    SetExpr,
     Stmt,
     TernaryExpr,
     TypeAssign,
@@ -232,14 +231,6 @@ class PythonAstJsonSerializer(
             "right": expr.right.accept(self),
         }
 
-    def visit_set_expr(self, expr: SetExpr) -> dict:
-        return {
-            "_type": "SetExpr",
-            "object": expr.object.accept(self),
-            "name": expr.name,
-            "value": expr.value.accept(self),
-        }
-
     def visit_cast_expr(self, expr: CastExpr) -> dict:
         return {
             "_type": "CastExpr",