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  1. ; two homework problems
  2.  
  3. (define (read-line . port)
  4.   (define (eat p c)
  5.     (if (and (not (eof-object? (peek-char p)))
  6.              (char=? (peek-char p) c))
  7.         (read-char p)))
  8.   (let ((p (if (null? port) (current-input-port) (car port))))
  9.     (let loop ((c (read-char p)) (line '()))
  10.       (cond ((eof-object? c) (if (null? line) c (list->string (reverse line))))
  11.             ((char=? #\newline c) (eat p #\return) (list->string (reverse line)))
  12.             ((char=? #\return c) (eat p #\newline) (list->string (reverse line)))
  13.             (else (loop (read-char p) (cons c line)))))))
  14.  
  15. (define (inflect xs)
  16.   (define (x i) (vector-ref xs i))
  17.   (let loop ((lo 0) (left-sum 0)
  18.              (hi (- (vector-length xs) 1))
  19.              (right-sum 0))
  20.     (cond ((< hi lo)
  21.             (values lo left-sum right-sum
  22.               (abs (- left-sum right-sum))))
  23.           ((< left-sum right-sum)
  24.             (loop (+ lo 1) (+ left-sum (x lo))
  25.                   hi right-sum))
  26.           (else (loop lo left-sum (- hi 1)
  27.                       (+ right-sum (x hi)))))))
  28.  
  29. (call-with-values
  30.   (lambda () (inflect '#(3 7 9 8 2 5 6)))
  31.   (lambda (point left-sum right-sum diff)
  32.     (display point) (newline)
  33.     (display left-sum) (newline)
  34.     (display right-sum) (newline)
  35.     (display diff) (newline)))
  36.  
  37. (define (tail n file-name)
  38.   (with-input-from-file file-name
  39.     (lambda ()
  40.       (let ((buffer (make-vector n "")))
  41.         (let loop ((i 0) (line (read-line)))
  42.           (cond ((eof-object? line)
  43.                   (do ((j 0 (+ j 1))) ((= j n))
  44.                     (display (vector-ref buffer (modulo (+ i j) n)))
  45.                     (newline)))
  46.           (else (vector-set! buffer i line)
  47.                 (loop (modulo (+ i 1) n)
  48.                       (read-line)))))))))
  49.  
  50. ; (tail 5 "bible.txt")
Success #stdin #stdout 0.01s 7272KB
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Standard input is empty
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3
19
21
2
https://ideone.com/Kz1XuS
language:
Scheme (chicken 4.13)
created:
8 years ago
visibility:
public

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