;; =================
;; Data definitions:

;; Light is one of:
;;  - "red"
;;  - "yellow"
;;  - "green"
;; interp. the current color of the light
;; <examples are redundant for enumerations>

#;
(define (fn-for-light l)
  (cond [(string=? l "red")    (...)]
        [(string=? l "yellow") (...)]
        [(string=? l "green")  (...)]))

;; Template rules used:
;;   one of: 3 cases
;;   atomic distinct: "red"
;;   atomic distinct: "yellow"
;;   atomic distinct: "green"



;; =================
;; Functions:

;; Light -> Light
;; called to run the animation; start with (main "red")
;; no tests for main function
(define (main l)
  (big-bang l
            (on-tick next-color 1)   ; Light -> Light
            (to-draw render-light))) ; Light -> Image




;; Light -> Light
;; produce next color of light
(check-expect (next-color "red")    "green")
(check-expect (next-color "yellow") "red")
(check-expect (next-color "green")  "yellow")

#;
(define (next-color l)      ; stub
  "red")
;<template from Light>

(define (next-color l)
  (cond [(string=? l "red")    "green"]
        [(string=? l "yellow") "red"]
        [(string=? l "green")  "yellow"]))



;; Light -> Image
;; produce appropriate image for light color
(check-expect (render-light "red")    RON)
(check-expect (render-light "yellow") YON)
(check-expect (render-light "green")  GON)

#;
(define (render-light l)
  BACKGROUND)
;<template from Light>

(define (render-light l)
  (cond [(string=? l "red")    RON]
        [(string=? l "yellow") YON]
        [(string=? l "green")  GON]))