feat(checker): improve function unwrapping

midas/checker/dispatcher.py

@@ -14,7 +14,6 @@ from midas.checker.types import (
     OverloadedFunction,
     Type,
     UnknownType,
-    unfold_type,
 )
 from midas.checker.unifier import Unifier
 
@@ -174,6 +173,33 @@ class CallDispatcher(Generic[E]):
                     message=message,
                 )
 
+    def _unwrap_function(
+        self,
+        callee: Type,
+        positional: list[TypedExpr[E]],
+        keywords: dict[str, TypedExpr[E]],
+    ) -> Union[tuple[Function, None], tuple[None, CallError]]:
+        match callee:
+            case DerivedType(type=base):
+                return self._unwrap_function(base, positional, keywords)
+
+            case GenericType():
+                unifier: Unifier = Unifier(self.types)
+                unified: Optional[Type] = unifier.unify_call(
+                    callee,
+                    [a[1] for a in positional],
+                    {k: v[1] for k, v in keywords.items()},
+                )
+                if unified is None:
+                    return None, CallError.IMPOSSIBLE_UNIFICATION
+                return self._unwrap_function(unified, positional, keywords)
+
+            case Function():
+                return callee, None
+
+            case _:
+                return None, CallError.NOT_CALLABLE
+
     def _are_arguments_valid(
         self,
         arguments: list[MappedArgument[E]],
@@ -222,13 +248,12 @@ class CallDispatcher(Generic[E]):
         """
         candidates: list[OverloadCandidate] = []
         for overload in overloads:
-            function: Type = unfold_type(overload)
-            if not isinstance(function, Function):
-                if report_errors:
-                    self.logger.error(
-                        f"Overload is not a function: {overload} is {function}"
-                    )
+            function, unwrap_error = self._unwrap_function(
+                overload, positional, keywords
+            )
+            if function is None:
                 continue
+
             valid, mapped = self.map_call_arguments(
                 function=function,
                 location=location,