Arthur Barraux
33 lines
581 B
Scheme
33 lines
581 B
Scheme
(==> (force (delay (+ 1 2))) 3)
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(==> (let ((p (delay (+ 1 2))))
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(list (force p) (force p))) (3 3))
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(assert (promise? (delay (+ 1 2))))
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; promises computed at most once
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(define count 0)
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(define p
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(delay
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(begin
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(set! count (+ count 1))
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(* x 3))))
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(define x 5)
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(==> count 0)
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(assert (promise? p))
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(==> (force p) 15)
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(assert (promise? p))
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(==> count 1)
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(==> (force p) 15)
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(==> count 1)
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(define (integers-starting-from n)
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(cons-stream n (integers-starting-from (+ n 1))))
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(assert (equal? (stream-head (integers-starting-from 0) 5) '(0 1 2 3 4)))
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