feat(checker): handle attribute getter

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 +1,9 @@
+# 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

midas/checker/checker.py

@@ -178,6 +178,13 @@ 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`
 
@@ -562,7 +569,24 @@ class Checker(
                 )
         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:

midas/resolver/midas.py

@@ -3,6 +3,7 @@ from typing import Optional
 import midas.ast.midas as m
 from midas.checker.types import (
     AliasType,
+    ComplexType,
     Operation,
     Type,
     UnknownType,
@@ -178,7 +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:
-            prop.accept(self)
-        # TODO
-        return UnknownType()
+        return ComplexType(
+            properties={
+                prop.name.lexeme: prop.type.accept(self) for prop in type.properties
+            }
+        )