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  1. ; extract number from string
  2.  
  3. (define (extract-number str)
  4.   (let loop ((cs (string->list str)) (prev #\X) (n 0))
  5.     (cond ((null? cs)
  6.             (* (if (char=? prev #\-) -1 1) n))
  7.           ((char-numeric? (car cs))
  8.             (loop (cdr cs) prev
  9.                   (+ (* n 10)
  10.                      (- (char->integer (car cs))
  11.                         (char->integer #\0)))))
  12.           ((positive? n)
  13.             (* (if (char=? prev #\-) -1 1) n))
  14.           (else (loop (cdr cs) (car cs) n)))))
  15.  
  16. (display (extract-number "-123")) (newline)
  17. (display (extract-number "-123junk")) (newline)
  18. (display (extract-number "junk-123")) (newline)
  19. (display (extract-number "junk-123junk")) (newline)
  20. (display (extract-number "junk-123junk456")) (newline)
  21. (display (extract-number "junk123junk456")) (newline)
Success #stdin #stdout 0.01s 50288KB
comments (?)
stdin
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Standard input is empty
stdout
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-123
-123
-123
-123
-123
123
https://ideone.com/cpk12l
language:
Scheme (guile 2.2.4)
created:
5 years ago
visibility:
public

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