(bind-func gui_validate
(lambda ()
;; check that all nodes are either full, or leaves
(null?
(Widget_find_preorder
(GUI_root EXTEMPORE_GUI)
(lambda (w)
;; need an exclusive or...
(not (or (and (null? (Widget_left_child w))
(null? (Widget_right_child w)))
(and (not (null? (Widget_left_child w)))
(not (null? (Widget_right_child w)))))))))))