Hello,
I have to make a traffic-light which changes color after each tick of
the computer.
So I thought this would work :
;; String -> Image
;; given a state of a trafic-light display a circle of the given color
if it's a color of the traffic-light otherwise error
(define (light color)
(cond
[(string=? color "oranje") (circle 10 "solid" "yellow")]
[(string=? color "rood") (circle 10 "solid" "red" )]
[(string=? color "groen") (circle 10 "solid" "green" )]
[else (error "Error : geen kleur van een verkeerslicht ingevoerd
in de functie" " light")]
))
;; World -> World
;; Given a World and set the traffic-light to the next color
(define (tock color)
( cond
[ (string=? color "oranje") "red"]
[ (string=? color "rood") "groen"]
[ (string=? color "groen") "oranje"]
))
(define (main color)
( big-bang color (on-tick tock) (to-draw light)))
(main "rood")
But the contents of color does not change so I get a error message.
What is the racket way to change the value of a string.
Roelof
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