Implement Closures (#28)

src/interpreted/interpreter.py

@@ -34,18 +34,20 @@
 
 
 class Scope:
-    def __init__(self):
+    def __init__(self, parent=None) -> None:
+        self.data = {}
+        self.parent = parent
         self.set("print", Print())
         self.set("len", Len())
         self.set("int", Int())
         self.set("float", Float())
         self.set("deque", DequeConstructor())
 
     def get(self, name) -> Any:
-        return getattr(self, name, NOT_SET)
+        return self.data.get(name, NOT_SET)
 
     def set(self, name, value) -> None:
-        setattr(self, name, value)
+        self.data[name] = value
 
 
 class InterpreterError(Exception):
@@ -170,8 +172,14 @@ def __init__(self, value: Object) -> None:
 
 
 class UserFunction(Function):
-    def __init__(self, definition: FunctionDef, current_globals: Scope) -> None:
+    def __init__(
+        self,
+        definition: FunctionDef,
+        parent_scope: Scope,
+        current_globals: Scope,
+    ) -> None:
         self.definition = definition
+        self.parent_scope = parent_scope
         self.current_globals = current_globals
 
     def as_string(self) -> str:
@@ -183,10 +191,10 @@ def arg_count(self) -> int:
     def call(self, interpreter: Interpreter, args: list[Object]) -> Object:
         super().ensure_args(args)
 
-        parent_scope = interpreter.scope
+        current_scope = interpreter.scope
         parent_globals = interpreter.globals
 
-        function_scope = Scope()
+        function_scope = Scope(parent=self.parent_scope)
         interpreter.globals = self.current_globals
         interpreter.scope = function_scope
 
@@ -201,7 +209,7 @@ def call(self, interpreter: Interpreter, args: list[Object]) -> Object:
             return ret.value
 
         finally:
-            interpreter.scope = parent_scope
+            interpreter.scope = current_scope
             interpreter.globals = parent_globals
 
         return Value(None)
@@ -424,7 +432,7 @@ def visit_Import(self, node: Import) -> None:
             self.scope = parent_scope
             self.globals = parent_globals
 
-            module_obj = Module(members=vars(module_scope))
+            module_obj = Module(members=module_scope.data)
 
             self.scope.set(name, module_obj)
 
@@ -451,7 +459,7 @@ def visit_ImportFrom(self, node: ImportFrom) -> None:
         for alias in node.names:
             name = alias.name
             if name == "*":
-                for member, value in vars(module_scope).items():
+                for member, value in module_scope.data.items():
                     self.scope.set(member, value)
                 return
 
@@ -462,7 +470,8 @@ def visit_ImportFrom(self, node: ImportFrom) -> None:
             self.scope.set(name, member)
 
     def visit_FunctionDef(self, node: FunctionDef) -> None:
-        function = UserFunction(node, self.globals)
+        parent_scope = self.scope
+        function = UserFunction(node, parent_scope, self.globals)
         self.scope.set(node.name, function)
 
     def visit_Assign(self, node: Assign) -> None:
@@ -734,12 +743,17 @@ def visit_Attribute(self, node: Attribute) -> Object:
     def visit_Name(self, node: Name) -> Value:
         name = node.id
 
-        value = self.scope.get(name)
+        current_scope = self.scope
+        while current_scope is not None:
+            value = current_scope.get(name)
+            if value is NOT_SET:
+                current_scope = current_scope.parent
+            else:
+                return value
 
+        value = self.globals.get(name)
         if value is NOT_SET:
-            value = self.globals.get(name)
-            if value is NOT_SET:
-                raise InterpreterError(f"{name!r} is not defined")
+            raise InterpreterError(f"{name!r} is not defined")
 
         return value
 

tests/interpreted_test.py

@@ -75,6 +75,26 @@ def foo(x):
             """,
             "a\nbc\nab\nabc\nb\n",
         ),
+        (
+            """\
+            x = 5
+
+            def bar():
+                x = 10
+
+                def baz():
+                    def foo():
+                        print(x)
+
+                    return foo
+
+                return baz
+
+            foo = bar()()
+            foo()
+            """,
+            "10\n",
+        ),
     ),
 )
 def test_interpret(source, output) -> None: