My pleasure.
Good on you for doing the exercise.
Here's a slightly modified version that:
- removes the use of set!: it's cleaner "functional" style to avoid
mutation where possible
- illustrates the use of match-define to unpack world
- other small tweaks and tricks
Dan
#lang racket
(require 2htdp/universe)
(require 2htdp/image)
(struct world (foreground background count))
(define (random-color)
(make-color (random 255) (random 255) (random 255)))
(define (next-state state)
(world (random-color)
(random-color)
(add1 (world-count state))))
(define (SUPER state)
(match-define (world fg bg n) state)
(overlay/align 'left 'top
(text (~a n) 30 "gray")
(overlay (text "SUPER" 105 fg)
(circle 200 "solid" bg))))
(big-bang (world (random-color) (random-color) 0)
(on-tick next-state 0.3)
(to-draw SUPER))
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