code rewritten to use a list rather than a structure.

list-of-bools.rkt

(require 2htdp/universe)
(require 2htdp/image)

;; a 16-bools is a list of booleans of length 16

;world -> world
;; a world is (make-world 16-bools)
;a world is (make-world boolean boolean boolean boolean)
(define-struct world (bools))

;; return the 'idx'th bool from the world
;; world number -> bool
(define (world-bool w idx)
  (list-ref (world-bools w) idx))

;; replace the 'n'th element of a list with a new value
;; list number any -> list
(define (list-replace lob idx new-val)
  (cond [(= idx 0) (cons new-val (rest lob))]
        [else (cons (first lob) (list-replace (rest lob) (sub1 idx) new-val))]))

(check-expect (list-replace (list false false false false) 2 "apple")
              (list false false "apple" false))

;; toggle the 'n'th element of a list from false to true and vice versa
;; list number -> list
(define (list-toggle lob idx )
  (cond [(= idx 0) (cons (not (first lob)) (rest lob))]
        [else (cons (first lob) (list-toggle (rest lob) (sub1 idx)))]))

(check-expect (list-toggle (list false false false false) 2)
              (list false false true false))

;; toggle the n-th bool in a world from true to false and vice versa
;; world number -> world
(define (toggle-bool w idx)
  (make-world (list-toggle (world-bools w) idx)))

;; WRITE A PURPOSE STATEMENT AND SIGNATURE FOR YOUR FUNCTION!
(define (buttons solid? z) (rectangle 70 40 (if solid? "solid" "outline") z))

;world -> image
;;> FIX THIS PURPOSE STATEMENT!
;circles takes a world and draws 4 circles over an empty-scene
(define (rect x)
  ;;> why do you need to pass "black" in everywhere?
  (place-image (buttons (world-bool x 3) "black") 350 50
  (place-image (buttons (world-bool x 2) "black") 250 50  
  (place-image (buttons (world-bool x 1) "black") 150 50  
  (place-image (buttons (world-bool x 0) "black") 50 50 
  (place-image (buttons (world-bool x 7) "black") 350 150  
  (place-image (buttons (world-bool x 6) "black") 250 150  
  (place-image (buttons (world-bool x 5) "black") 150 150  
  (place-image (buttons (world-bool x 4) "black") 50 150
  (place-image (buttons (world-bool x 11) "black") 350 250  
  (place-image (buttons (world-bool x 10) "black") 250 250  
  (place-image (buttons (world-bool x 9) "black") 150 250  
  (place-image (buttons (world-bool x 8) "black") 50 250
  (place-image (buttons (world-bool x 15) "black") 350 350  
  (place-image (buttons (world-bool x 14) "black") 250 350  
  (place-image (buttons (world-bool x 13) "black") 150 350  
  (place-image (buttons (world-bool x 12) "black") 50 350(empty-scene 400 400))))))))))))))))))

;world key -> world
;changes the state of whichever world-field-name corresponds to the key pressed to the opposite value
(check-expect (change (make-world (list false false false false false false false false false false false false false false false false)) "1") 
              (make-world (list true false false false false false false false false false false false false false false false)))
(check-expect (change (make-world (list false true false true false false false false false false false false false false false false)) "4") 
              (make-world (list false true false false false false false false false false false false false false false false)))



;;> PURPOSE STATEMENT AND SIGNATURE!
(define (change x y)
   (cond
     [(key=? y "1") (toggle-bool x 0)]
     [(key=? y "2") (toggle-bool x 1)]
     [(key=? y "3") (toggle-bool x 2)]
     [(key=? y "4") (toggle-bool x 3)]
     [(key=? y "q") (toggle-bool x 4)]
     [(key=? y "w") (toggle-bool x 5)]
     [(key=? y "e") (toggle-bool x 6)]
     [(key=? y "r") (toggle-bool x 7)]
     [(key=? y "a") (toggle-bool x 8)]
     [(key=? y "s") (toggle-bool x 9)]
     [(key=? y "d") (toggle-bool x 10)]
     [(key=? y "f") (toggle-bool x 11)]
     [(key=? y "z") (toggle-bool x 12)]
     [(key=? y "x") (toggle-bool x 13)]
     [(key=? y "c") (toggle-bool x 14)]
     [(key=? y "v") (toggle-bool x 15)]
     [else x]))



(big-bang (make-world (list false false false false false false false false false false false false false false false false)) (to-draw rect) (on-key change) (on-release change))