102 lines
3.4 KiB
Scheme
102 lines
3.4 KiB
Scheme
;; TeachPack: pingp.ss
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;; Language: Advanced
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;; This file tests the trace functions. It is not used anywhere else.
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;; Speed and its relationship to positions
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;; ---------------------------------------
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(define-struct speed (x y))
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;; posn+ : posn vec -> vec
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(define (posn+ p v)
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(make-posn (+ (posn-x p) (speed-x v)) (+ (posn-y p) (speed-y v))))
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;; posn*s : number vec -> posn
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(define (posn*s f p)
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(make-speed (* f (speed-x p)) (* f (speed-y p))))
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;; vec* : vec vec -> vec
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(define (vec* v1 v2)
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(make-speed (* (speed-x v1) (speed-x v2)) (* (speed-y v1) (speed-y v2))))
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;; The ball representation and some basic primitives:
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;; ---------------------------------------------------
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(define-struct ball (posn speed))
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;; make-direction : (speed -> num) X Y -> (ball -> (union X Y))
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(define (make-direction access dir1 dir2)
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(lambda (ball)
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(cond
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((< (access (ball-speed ball)) 0) dir1)
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((> (access (ball-speed ball)) 0) dir2)
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(else (error 'make-direction "can't happen")))))
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;; ns-direction : ball -> {'NORTH, 'SOUTH}
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(define ns-direction (make-direction speed-y 'NORTH 'SOUTH))
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;; ew-direction : ball -> {'EAST, 'WEST}
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(define ew-direction (make-direction speed-x 'WEST 'EAST))
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;; make-distance : (posn -> num) (ball -> sym) sym num num -> (ball -> num)
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(define (make-distance direction access dir bound1 bound2)
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(lambda (ball)
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(if (eq? (direction ball) dir)
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(- (access (ball-posn ball)) bound1)
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(- bound2 (access (ball-posn ball))))))
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;; make-time : (ball -> num) (speed -> num) -> (ball -> number)
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(define (make-time distance access)
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(lambda (ball)
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(/ (distance ball) (abs (access (ball-speed ball))))))
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;; ns-time-to-wall : ball -> number (time before ns wall is hit)
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(define ns-time-to-wall
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(make-time (make-distance ns-direction posn-y 'NORTH NORTH SOUTH) speed-y))
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;; ew-time-to-wall : ball -> number (time before ew wall is hit)
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(define ew-time-to-wall
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(make-time (make-distance ew-direction posn-x 'WEST WEST EAST) speed-x))
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;; Moving a Ball
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;; -------------
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;; move-in-box : ball number -> ball
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(define (move-in-box ball t)
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(case (bounces-from ball t)
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((NORTH SOUTH) (bouncing-move ns-bounce (ns-time-to-wall ball) t ball))
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((EAST WEST) (bouncing-move ew-bounce (ew-time-to-wall ball) t ball))
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(else (move-ball ball t))))
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;; bouncing-move : (ball -> ball) num num ball -> ball
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(define (bouncing-move bounce t-bounce t ball)
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(move-in-box (bounce (move-ball ball t-bounce)) (- t t-bounce)))
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;; bounces-from : ball number -> {'NORTH, 'SOUTH, 'EAST, 'WEST, 'none}
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(define (bounces-from ball t)
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(cond
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((<= (ns-time-to-wall ball) (min (ew-time-to-wall ball) t)) (ns-direction ball))
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((<= (ew-time-to-wall ball) (min t (ns-time-to-wall ball))) (ew-direction ball))
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(else 'none)))
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;; move : ball number -> ball
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(define (move-ball ball t)
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(make-ball (posn+ (ball-posn ball) (posn*s t (ball-speed ball))) (ball-speed ball)))
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;; make-bounce : speed -> (ball -> ball)
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(define (make-bounce bounceV)
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(lambda (ball)
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(make-ball (ball-posn ball) (vec* (ball-speed ball) bounceV))))
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;; ns-bounce : ball -> ball
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(define ns-bounce (make-bounce (make-speed 1 -1)))
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;; ew-bounce-west : ball -> ball
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(define ew-bounce (make-bounce (make-speed -1 1)))
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;; mover : posn speed number -> posn
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(define (mover p s t)
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(posn+ p (posn*s t s)))
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(trace-ball (make-ball (make-posn 100 100) (make-speed 8 -2)) ball-posn move-in-box 222)
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(trace (make-posn 100 100) (make-speed 8 -2) mover 222)
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