21 lines
518 B
Scheme
21 lines
518 B
Scheme
#lang scheme/gui
|
|
|
|
(require 2htdp/universe)
|
|
(require 2htdp/image)
|
|
|
|
(define s "")
|
|
(define x 1)
|
|
|
|
(big-bang 1
|
|
(on-tick (lambda (w)
|
|
(begin
|
|
(set! x (+ x 1))
|
|
(if (= x 3) 0 1))))
|
|
(stop-when zero?)
|
|
(on-draw (lambda (w)
|
|
(begin
|
|
(set! s (string-append "-" s))
|
|
(rectangle 1 1 'solid 'green)))))
|
|
|
|
(unless (string=? s "---") (error 'world-update-test "failed! ~s" s))
|