link="#009900" vlink="#007700" alink="#cc0000"> Teachpacks for How to Design Programs

Arrows GUI

arrow-gui.ss

The teachpack arrow-gui.ss implements three functions:

control : -> symbol
to read out the current state of the message field

view : (union string symbol) -> true
to display its argument in the message field

modelT = (button% event% -> true)
connect : modelT modelT modelT modelT -> true
to connect four controllers with the four directions in the arrow window

Example:

> (define (make-model dir)
   (lambda (b e)
     (begin
       (view dir)
       (printf "~a ~n" (control)))))

> (connect
   (make-model "left")
   (make-model "right")
   (make-model "up")
   (make-model "down"))

Now click on the four arrows. The message field will contain the current direction, the print-out the prior contents of the message field.