feat(checker): add cast expression

examples/01_simple_type_checking/02_simple_types.py

@@ -3,6 +3,6 @@
 
 midas.using("02_simple_types.midas")
 
-distance: Meter = 123.45
-time: Second = 6.7
+distance: Meter = cast(Meter, 123.45)
+time: Second = cast(Second, 6.7)
 speed = distance / time

midas/checker/checker.py

@@ -291,6 +291,9 @@ class Checker(
 
     def visit_set_expr(self, expr: p.SetExpr) -> Type: ...
 
+    def visit_cast_expr(self, expr: p.CastExpr) -> Type:
+        return expr.type.accept(self)
+
     def visit_base_type(self, node: p.BaseType) -> Type:
         return self.ctx.get_type(node.base)
 

midas/resolver/resolver.py

@@ -114,3 +114,6 @@ class Resolver(p.Stmt.Visitor[None], p.Expr.Visitor[None]):
     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/cases/checker/04_custom_types.py

@@ -3,6 +3,6 @@
 
 midas.using("04_custom_types.midas")
 
-distance: Meter = 123.45
-time: Second = 6.7
+distance: Meter = cast(Meter, 123.45)
+time: Second = cast(Second, 6.7)
 speed = distance / time

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

@@ -1,32 +1,3 @@
 {
-  "diagnostics": [
-    {
-      "type": "Error",
-      "location": {
-        "start": [
-          6,
-          0
-        ],
-        "end": [
-          6,
-          24
-        ]
-      },
-      "message": "Cannot assign BaseType(name='float') to distance of type SimpleType(name='Meter', base=BaseType(name='float'))"
-    },
-    {
-      "type": "Error",
-      "location": {
-        "start": [
-          7,
-          0
-        ],
-        "end": [
-          7,
-          18
-        ]
-      },
-      "message": "Cannot assign BaseType(name='float') to time of type SimpleType(name='Second', base=BaseType(name='float'))"
-    }
-  ]
+  "diagnostics": []
 }