diff --git a/midas/checker/midas.py b/midas/checker/midas.py
index decb40c..6a528a0 100644
--- a/midas/checker/midas.py
+++ b/midas/checker/midas.py
@@ -8,6 +8,7 @@ from midas.checker.reporter import FileReporter, Reporter
 from midas.checker.types import (
     AliasType,
     ComplexType,
+    ExtensionType,
     Function,
     GenericType,
     Type,
@@ -76,7 +77,7 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[None], m.Type.Visitor[Type
         self.types.define_type(name, type)
         self._local_variables.clear()
 
-    def visit_property_stmt(self, stmt: m.PropertyStmt) -> None: ...
+    def visit_member_stmt(self, stmt: m.MemberStmt) -> None: ...
 
     def visit_extend_stmt(self, stmt: m.ExtendStmt) -> None:
         self._resolve_type_params(stmt.params)
@@ -126,16 +127,21 @@ class MidasTyper(m.Stmt.Visitor[None], m.Expr.Visitor[None], m.Type.Visitor[Type
         # TODO
         return UnknownType()
 
-    def visit_complex_type(self, type: m.ComplexType) -> Type:
+    def visit_complex_type(self, type: m.ComplexType) -> ComplexType:
         return ComplexType(
-            properties={
-                prop.name.lexeme: prop.type.accept(self) for prop in type.properties
+            members={
+                member.name.lexeme: member.type.accept(self) for member in type.members
             }
         )
 
+    def visit_extension_type(self, type: m.ExtensionType) -> Type:
+        return ExtensionType(
+            base=type.base.accept(self),
+            extension=self.visit_complex_type(type.extension),
+        )
+
     def visit_function_type(self, type: m.FunctionType) -> Type:
         return Function(
-            name="<anonymous>",
             pos_args=[
                 Function.Argument(
                     pos=i,
diff --git a/midas/checker/python.py b/midas/checker/python.py
index c11ee22..3d44975 100644
--- a/midas/checker/python.py
+++ b/midas/checker/python.py
@@ -12,6 +12,7 @@ from midas.checker.reporter import FileReporter, Reporter
 from midas.checker.resolver import Resolver
 from midas.checker.types import (
     ComplexType,
+    ExtensionType,
     Function,
     Operation,
     Type,
@@ -192,7 +193,6 @@ class PythonTyper(
             returns_hint = stmt.returns.accept(self)
             # Early define to handle simple fully-typed recursion
             inside_function: Function = Function(
-                name=stmt.name,
                 pos_args=pos_args,
                 args=args,
                 kw_args=kw_args,
@@ -227,7 +227,6 @@ class PythonTyper(
 
         # TODO: handle *args and **kwargs sinks
         function: Function = Function(
-            name=stmt.name,
             pos_args=pos_args,
             args=args,
             kw_args=kw_args,
@@ -250,8 +249,9 @@ class PythonTyper(
             case p.VariableExpr():
                 self._assign_var(location, target, value_type)
 
-            case p.GetExpr():
-                self._assign_attr(location, target, value_type)
+            case p.GetExpr(object=object, name=name):
+                object_type: Type = self.type_of(object)
+                self._assign_attr(location, object_type, name, value_type)
 
             case _:
                 if not isinstance(target, p.VariableExpr):
@@ -276,32 +276,43 @@ class PythonTyper(
                     f"Cannot assign {value_type} to variable '{name}' of type {var_type}",
                 )
 
-    def _assign_attr(self, location: Location, target: p.GetExpr, value_type: Type):
-        object: Type = self.type_of(target.object)
+    def _assign_attr(
+        self, location: Location, object: Type, name: str, value_type: Type
+    ):
+        # TODO: improve recursion to have better error messages
         base_object: Type = unfold_type(object)
         match base_object:
-            case ComplexType(properties=properties):
-                if target.name not in properties:
+            case ComplexType(members=members):
+                if name not in members:
+                    self.reporter.error(location, f"Unknown member '{object}.{name}'")
+                    return
+
+                member_type: Type = members[name]
+                if not self.is_subtype(value_type, member_type):
                     self.reporter.error(
-                        target.location, f"Unknown property '{object}.{target.name}'"
+                        location,
+                        f"Cannot assign {value_type} to member '{object}.{name}' of type {member_type}",
                     )
                     return
 
-                prop_type: Type = properties[target.name]
-                if not self.is_subtype(value_type, prop_type):
-                    self.reporter.error(
-                        location,
-                        f"Cannot assign {value_type} to property '{object}.{target.name}' of type {prop_type}",
-                    )
-                    return
+            case ExtensionType(base=base, extension=ComplexType(members=members)):
+                if name in members:
+                    member_type: Type = members[name]
+                    if not self.is_subtype(value_type, member_type):
+                        self.reporter.error(
+                            location,
+                            f"Cannot assign {value_type} to member '{object}.{name}' of type {member_type}",
+                        )
+                        return
+                return self._assign_attr(location, base, name, value_type)
 
             case UnknownType():
                 pass
 
             case _:
                 self.reporter.error(
-                    target.location,
-                    f"Cannot assign {value_type} to unknown property '{object}.{target.name}'",
+                    location,
+                    f"Cannot assign {value_type} to unknown property '{object}.{name}'",
                 )
 
     def visit_return_stmt(self, stmt: p.ReturnStmt) -> None:
@@ -422,23 +433,37 @@ class PythonTyper(
 
     def visit_get_expr(self, expr: p.GetExpr) -> Type:
         object: Type = self.type_of(expr.object)
+        member: Optional[Type] = self._get_member(object, expr.name)
+        if member is None:
+            self.reporter.error(
+                expr.location, f"Unknown property '{expr.name}' on {object}"
+            )
+            return UnknownType()
+        self.logger.debug(f"Property '{expr.name}' on {object} has type {member}")
+        return member
+
+    def _get_member(self, object: Type, name: str) -> Optional[Type]:
         base_object: Type = unfold_type(object)
         match base_object:
-            case ComplexType(properties=properties):
-                if expr.name not in properties:
-                    self.reporter.error(
-                        expr.location, f"Unknown property '{expr.name} on {object}"
-                    )
-                    return UnknownType()
-                return properties[expr.name]
+            case ComplexType(members=members):
+                if name in members:
+                    return members[name]
+                self.logger.debug(f"No property '{name}' in {base_object}")
+                return None
+
+            case ExtensionType(base=base, extension=ComplexType(members=members)):
+                if name in members:
+                    return members[name]
+                self.logger.debug(
+                    f"No property '{name}' on {base_object}, looking up in base"
+                )
+                return self._get_member(base, name)
 
             case UnknownType():
                 return UnknownType()
 
             case _:
-                self.reporter.error(
-                    expr.location, f"Cannot get property '{expr.name}' on {object}"
-                )
+                self.logger.debug(f"Can't get property on {base_object}")
                 return UnknownType()
 
     def visit_literal_expr(self, expr: p.LiteralExpr) -> Type:
diff --git a/midas/checker/types.py b/midas/checker/types.py
index 41ad786..9057e4c 100644
--- a/midas/checker/types.py
+++ b/midas/checker/types.py
@@ -35,7 +35,6 @@ class UnitType:
 
 @dataclass(frozen=True, kw_only=True)
 class Function:
-    name: str
     pos_args: list[Argument]
     args: list[Argument]
     kw_args: list[Argument]
@@ -56,7 +55,7 @@ class Function:
                 args.append("*")
             args += list(map(str, self.kw_args))
 
-        return f"{self.name}({', '.join(args)}) -> {self.returns}"
+        return f"({', '.join(args)}) -> {self.returns}"
 
     @dataclass(frozen=True, kw_only=True)
     class Argument:
@@ -72,13 +71,22 @@ class Function:
 
 @dataclass(frozen=True, kw_only=True)
 class ComplexType:
-    properties: dict[str, Type]
+    members: dict[str, Type]
 
     def __str__(self) -> str:
-        props: list[str] = [f"{name}: {type}" for name, type in self.properties.items()]
+        props: list[str] = [f"{name}: {type}" for name, type in self.members.items()]
         return f"{{{', '.join(props)}}}"
 
 
+@dataclass(frozen=True, kw_only=True)
+class ExtensionType:
+    base: Type
+    extension: ComplexType
+
+    def __str__(self) -> str:
+        return f"{self.base} & {self.extension}"
+
+
 @dataclass(frozen=True, kw_only=True)
 class Operation:
     signature: CallSignature
@@ -145,26 +153,35 @@ def substitute_typevars(type: Type, substitutions: dict[str, Type]) -> Type:
             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] = {
+        case ComplexType(members=members):
+            members2: dict[str, Type] = {
                 name: substitute_typevars(prop, substitutions)
-                for name, prop in properties.items()
+                for name, prop in members.items()
             }
-            return ComplexType(properties=properties2)
+            return ComplexType(members=members2)
+
+        case ExtensionType(base=base, extension=ComplexType(members=members)):
+            return ExtensionType(
+                base=substitute_typevars(base, substitutions),
+                extension=ComplexType(
+                    members={
+                        name: substitute_typevars(prop, substitutions)
+                        for name, prop in members.items()
+                    }
+                ),
+            )
 
         case TypeVar(name=name):
             if name in substitutions:
@@ -193,6 +210,7 @@ Type = (
     | UnitType
     | Function
     | ComplexType
+    | ExtensionType
     | TypeVar
     | GenericType
     | AppliedType