On Oct 20, 2011, at 3:53 AM, Stephen Bloch wrote: > > On Oct 20, 2011, at 1:20 AM, John Clements wrote: > >> I'm pleased to report that the sound library works pretty transparently with >> the universe teachpack. >> ... >> (define (accelerate b) >> (cond [(and (<= (ball-posn b) 6) >> (<= (ball-vel b) 0)) >> (begin (play pop) >> (make-ball 6 (- (ball-vel b))))] >> [else >> (make-ball (+ (ball-posn b) (ball-vel b)) >> (- (ball-vel b) 1))])) >> ... >> The larger question could potentially be whether the sound-playing should be >> less imperative. If you wanted, you could add a "to-play" along with >> "to-draw", and just make the sound-playing part of the world state. This >> would avoid the "begin". > > > "to-play" MIGHT be a good way to do things, but in many cases (including the > above "accelerate" example) it'll be more natural to specify a sound as you > determine the new world, rather than as a separate function of the state of > the world. It's analogous to the difference between "stop-when" and > "stop-with". One could provide this ability very simply: > > (define (play-with sound world) > (begin (play sound) world))
Yes, but how do you write test cases for this? John
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