Definitions infer stack effects.

At start-up defs that DON'T type check are permitted (so you can use e.g.
loop, map, etc.) in the definitions "source", but then the user-facing
inscribe command only allows you to define new commands that DO
type-check.  The ideal solution here is to get inference working for the
loopy words.  (In the meantime you can select and execute their
definition text directly.  That's not (yet!) type-checked.)

joy/gui/world.py

@@ -23,7 +23,7 @@ from inspect import getdoc
 from joy.joy import run
 from joy.parser import Symbol
 from joy.utils.stack import stack_to_string
-from joy.utils.polytypes import type_check
+from joy.utils.types import type_check
 
 
 def is_numerical(s):