65 lines
1.3 KiB
Scheme
65 lines
1.3 KiB
Scheme
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; Copyright (c) 1994 by Richard Kelsey. See file COPYING.
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(define (fact n)
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(let loop ((i n) (r 1))
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(if (<= i 1)
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r
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(loop (- i 1) (* i r)))))
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(define (default y) y)
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(define do-it (make-vector 5))
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(do ((i 0 (+ i 1)))
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((>= i 5))
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(vector-set! do-it i default))
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(define (add-entry i k)
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(let ((f (fact k)))
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(vector-set! do-it i (lambda (x) (+ x f)))))
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(add-entry 0 1)
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;(add-entry 1 1)
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(add-entry 2 3)
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(add-entry 3 4)
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(add-entry 4 4)
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(define (test x)
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((vector-ref do-it x) 5))
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(define (main)
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(write-number (test (read-number (current-input-port)))
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(current-output-port)))
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(define (digit? ch)
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(let ((ch (char->ascii ch)))
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(and (>= ch (char->ascii #\0))
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(<= ch (char->ascii #\9)))))
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(define (read-number port)
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(let loop ((r 0))
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(ps-read-char port
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(lambda (ch)
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(cond ((digit? ch)
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(loop (+ (- (char->ascii ch) (char->ascii #\0))
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(* r 10))))
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(else r)))
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(lambda () 0))))
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(define (write-number x port)
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(really-write-number (cond ((< x 0)
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(write-char #\- port)
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(- 0 x))
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(else
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x))
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port)
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(newline port))
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(define (really-write-number x port)
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(if (>= x 10)
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(really-write-number (quotient x 10) port))
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(write-char (ascii->char (+ (remainder x 10)
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(char->ascii #\0)))
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port))
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