Fix missing module qualifier bug.

stepper.py

@@ -360,7 +360,7 @@ def ty2base_ty(ty, tdecs, seen=[]):
             return ty2base_ty(tdecs[other_name].body, tdecs, [other_name] + seen)
         else:
             err('Could not find type {} in gloval type environment:\n{}'
-                .format(ty2s(ty), tdecs.keys()))
+                .format(ll.ty2s(ty), tdecs.keys()))
             return ll.SimpleType.Void
     else:
         # TODO