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私は BSL でブレークアウトをプログラムしようとしてきましたが、現在行き詰まっています。ボールが底にぶつかったときにゲームをリセットしようとしていますが、エラーメッセージがわかりません。今いろいろ試してみました。何か考えはありますか？

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

(define WIDTH 200)
(define HEIGHT 200)
(define BALL-IMG (circle 10 "solid" "red"))
(define BALL-RADIUS (/ (image-width BALL-IMG) 2))

(define-struct vel (delta-x delta-y))
; a Vel is a structure: (make-vel Number Number)
; interp. the velocity vector of a moving object

(define-struct ball (loc velocity))
; a Ball is a structure: (make-ball Posn Vel)
; interp. the position and velocity of a object 

; Posn Vel -> Posn
; applies q to p and simulates the movement in one clock tick
(check-expect (posn+vel (make-posn 5 6) (make-vel 1 2))
              (make-posn 6 8))
(define (posn+vel p q)
  (make-posn (+ (posn-x p) (vel-delta-x q))
             (+ (posn-y p) (vel-delta-y q))))


; Ball -> Ball
; computes movement of ball in one clock tick
(check-expect (move-ball (make-ball (make-posn 20 30)
                                    (make-vel 5 10)))
              (make-ball (make-posn 25 40)
                         (make-vel 5 10)))
(define (move-ball ball)
  (make-ball (posn+vel (ball-loc ball)
                       (ball-velocity ball))
             (ball-velocity ball)))

; A Collision is either
; - "top"
; - "down"
; - "left"
; - "right"
; - "none"
; interp. the location where a ball collides with a wall

; Posn -> Collision
; detects with which of the walls (if any) the ball collides
(check-expect (collision (make-posn 0 12))  "left")
(check-expect (collision (make-posn 15 HEIGHT)) "down")
(check-expect (collision (make-posn WIDTH 12))  "right")
(check-expect (collision (make-posn 15 0)) "top")
(check-expect (collision (make-posn 55 55)) "none")
(define (collision posn)
  (cond
    [(<= (posn-x posn) BALL-RADIUS) "left"]
    [(<= (posn-y posn) BALL-RADIUS)  "top"]
    [(>= (posn-x posn) (- WIDTH BALL-RADIUS)) "right"]
    [(>= (posn-y posn) (- HEIGHT BALL-RADIUS)) "down"]
    [else "none"]))

; Vel Collision -> Vel  
; computes the velocity of an object after a collision
(check-expect (bounce (make-vel 3 4) "left")
              (make-vel -3 4))
(check-expect (bounce (make-vel 3 4) "top")
              (make-vel 3 -4))
(check-expect (bounce (make-vel 3 4) "none")
              (make-vel 3 4))
(define (bounce vel collision)
  (cond [(or (string=? collision "left")
             (string=? collision "right"))
         (make-vel (- (vel-delta-x vel))
                   (vel-delta-y vel))]
        [(string=? collision "top")
         (make-vel (vel-delta-x vel)
                   (- (vel-delta-y vel)))]
        [(string=? collision "down")  (tick (render INITIAL-BALL))]
        [else vel]))

; WorldState is a Ball

; WorldState -> Image
; renders ball at its position
(check-expect (image? (render INITIAL-BALL)) #true)
(define (render ball)
  (place-image BALL-IMG
               (posn-x (ball-loc ball))
               (posn-y (ball-loc ball))
               (empty-scene WIDTH HEIGHT)))


; WorldState -> WorldState
; moves ball to its next location
(check-expect (tick (make-ball (make-posn 20 12) (make-vel 1 2)))
              (make-ball (make-posn 21 14) (make-vel 1 2)))
(define (tick ball)
  (move-ball (make-ball (ball-loc ball)
                        (bounce (ball-velocity ball)
                                (collision (ball-loc ball))))))

(define INITIAL-BALL (make-ball (make-posn 20 12)
                                (make-vel 1 2)))


 ; start with: (main INITIAL-BALL)
(define (main ws)
  (big-bang ws (on-tick tick 0.01) (to-draw render)))
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2 に答える 2

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Ty Coghlan の優れた回答に少し追加すると、check-expectあなたのbounce機能には 1 つだけ欠けていることを指摘したいと思います...そしてそれはあなたに問題を引き起こしたものです!

1 つのヒント: BSL では、テストしていない部分を示す黒とオレンジのハイライトが表示されます。

于 2015-12-12T05:08:53.443 に答える
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バウンス関数で、string=? collision downブランチを returnに変更します

(make-vel (vel-delta-x vel) (- (vel-deltay vel))). 現在、ティック関数が処理方法がわからない画像を返しています。乾杯！

于 2015-12-11T17:45:26.843 に答える