Reverse tokens instead of temp lists.

This way we can build the tuples representing the Thun lists as we go
and I bet it's more efficient, eh?

implementations/Python/joy.py

@@ -349,22 +349,21 @@ def text_to_expression(text):
     :rtype: stack
     :raises ParseError: if the parse fails.
     '''
-    frame = []
+    lists = []
-    stack = []
+    stack = ()
 
-    for tok in text.replace('[', ' [ ').replace(']', ' ] ').split():
+    for tok in reversed(text.replace('[', ' [ ').replace(']', ' ] ').split()):
 
         if tok == '[':
-            stack.append(frame)
+            if not lists:
-            frame = []
+                raise ParseError('Unclosed bracket.')
+            thing, stack = stack, lists.pop()
+
+        elif tok == ']':
+            lists.append(stack)
+            stack = ()
             continue
 
-        if tok == ']':
-            thing = list_to_stack(frame)
-            try:
-                frame = stack.pop()
-            except IndexError:
-                raise ParseError('Extra closing bracket.') from None
         elif tok == _T:
             thing = True
         elif tok == _F:
@@ -375,12 +374,12 @@ def text_to_expression(text):
             except ValueError:
                 thing = Symbol(tok)
 
-        frame.append(thing)
+        stack = thing, stack
 
-    if stack:
+    if lists:
-        raise ParseError('Unclosed bracket.')
+        raise ParseError('Extra closing bracket.')
 
-    return list_to_stack(frame)
+    return stack
 
 
 '''