;; 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-intermediate-lambda-reader.ss" "lang")((modname |25.1|) (read-case-sensitive #t) (teachpacks ((lib "draw.ss" "teachpack" "htdp") (lib "arrow.ss" "teachpack" "htdp") (lib "gui.ss" "teachpack" "htdp"))) (htdp-settings #(#t constructor repeating-decimal #f #t none #f ((lib "draw.ss" "teachpack" "htdp") (lib "arrow.ss" "teachpack" "htdp") (lib "gui.ss" "teachpack" "htdp")))))
(define-struct ball (radius x y delta-x delta-y color))

;A ball is a structure
;(make-ball number number number number number symbol)

;draw-and-clear-ball : ball -> true
(define (draw-and-clear-ball a-ball)
  (and (draw-solid-disk (make-posn (ball-x a-ball)
                                   (ball-y a-ball))
                        (ball-radius a-ball)
                        (ball-color a-ball))
       (sleep-for-a-while DELAY)
       (clear-solid-disk (make-posn (ball-x a-ball)
                                    (ball-y a-ball))
                         (ball-radius a-ball)
                         (ball-color a-ball))))

;move-ball : ball -> ball
(define (move-ball a-ball)
  (make-ball (ball-radius a-ball)
             (+ (ball-x a-ball) (ball-delta-x a-ball))
             (+ (ball-y a-ball) (ball-delta-y a-ball))
             (ball-delta-x a-ball)
             (ball-delta-y a-ball)
             (ball-color a-ball)))

;out-of-bounds? : ball -> boolean
(define (out-of-bounds? a-ball)
  (not (and (<= 0 (ball-x a-ball) WIDTH)
            (<= 0 (ball-y a-ball) HEIGHT))))

;move-until-out : ball -> true
;Move the ball until it is out of bounds.

(define (move-until-out a-ball)
  (cond
    [(out-of-bounds? a-ball) true]
    [(draw-and-clear-ball a-ball) (move-until-out (move-ball a-ball))]))

(define VOLLEYBALL (make-ball 20 0 0 5 2 'black))
(define BEACHBALL (make-ball 50 25 25 3 2 'green))
(define BASEBALL (make-ball 10 470 470 -10 -14 'blue))
(define TENNISBALL (make-ball 8 470 20 -6 8 'yellow))

(define LISTOFBALLS (list VOLLEYBALL
                          BEACHBALL
                          BASEBALL
                          TENNISBALL))


;move-balls : (listof balls) -> true
;Moves alob (listof balls).

(define (move-balls alob)
  (andmap move-until-out alob))

;move-simultaneous : (listof balls) -> true
;Moves alob simultaneously.

(define (move-simultaneous alob)
  (cond
    [(andmap out-of-bounds? alob) true]
    [else (and (andmap draw-and-clear-ball alob)
               (move-simultaneous (map move-ball alob)))]))

(define WIDTH 500)
(define HEIGHT 500)
(define DELAY 1)
(start WIDTH HEIGHT)
;(move-balls LISTOFBALLS)
(move-simultaneous LISTOFBALLS)
(stop)