;; The first three lines of this file were inserted by DrScheme. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-beginner-reader.ss" "lang")((modname 17.1.7) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ())))
(require installed-teachpacks/picturing-programs)

; Worked Exercise 17.1.7

#|
; A shape-color is one of the strings "red", "green", or "blue".
(check-expect (function-on-shape-color "red") ...)
(check-expect (function-on-shape-color "green") ...)
(check-expect (function-on-shape-color "blue") ...)

(define (function-on-shape-color c)
  (cond [(string=? c "red") ...]
        [(string=? c "green") ...]
        [(string=? c "blue") ...]
        ))

(check-expect (function-returning-shape-color ...) "red")
(check-expect (function-returning-shape-color ...) "green")
(check-expect (function-returning-shape-color ...) "blue")

(define (function-returning-shape-color ...)
  (cond [... "red"]
        [... "green"]
        [... "blue"]
        ))
|#

; shape-color? : anything -> boolean
(check-expect (shape-color? "red") true)
(check-expect (shape-color? "green") true)
(check-expect (shape-color? "blue") true)
(check-expect (shape-color? "purple") false)
(check-expect (shape-color? "beluga") false)
(check-expect (shape-color? 17) false)

(define (shape-color? thing)
  (and (string? thing)
       (or (string=? thing "red")
           (string=? thing "green")
           (string=? thing "blue"))))


; model is a shape-color
; draw handler show-triangle : shape-color -> image
(check-expect (show-triangle "red") (triangle 30 "solid" "red"))
(check-expect (show-triangle "green") (triangle 30 "solid" "green"))
(check-expect (show-triangle "blue") (triangle 30 "solid" "blue"))
(define (show-triangle c)
  (triangle 30 "solid" c))

; tick handler next-color : shape-color -> shape-color
(check-expect (next-color "red") "green")
(check-expect (next-color "green") "blue")
(check-expect (next-color "blue") (stop-with "blue"))

(define (next-color c)
  ; c      shape-color
  (cond [(string=? c "red") "green"]
        [(string=? c "green") "blue"]
        [(string=? c "blue") (stop-with "blue")]
        ))

(big-bang "red"
          (check-with shape-color?)
          (on-draw show-triangle)
          (on-tick next-color 2))