[plt-scheme] setting variables

From: Avi (n4alpaca at gmail.com)
Date: Sun Jan 24 23:14:46 EST 2010

How do I set a variable used in a mathematical function using set!,
based upon what is put into a text-field (I'm using gui.ss)

example:
(define (Math x)
    (+ 1 a d)
 if user types "H" into text-box 1 than (set! a (+ a 1) and if user
types "O" into text-box 2 than (set! d (- d 2).


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