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  1. ; circular arrays
  2.  
  3. (define (make-queue n)
  4.   (let ((q (make-vector n #f))
  5.         (start 0) (end 0) (size 0))
  6.     (lambda (command . args)
  7.       (case command
  8.       ((empty?) (zero? size))
  9.       ((enqueue)
  10.         (if (= n size)
  11.             (error 'enqueue "Full")
  12.             (begin
  13.               (set! size (+ size 1))
  14.               (vector-set! q end (car args))
  15.               (set! end (modulo (+ end 1) n)))))
  16.       ((dequeue)
  17.         (if (zero? size)
  18.             (error 'enqueue "Empty")
  19.             (let ((x (vector-ref q start)))
  20.               (set! size (- size 1))
  21.               (vector-set! q start #f)
  22.               (set! start (modulo (+ start 1) n))
  23.               x)))))))
  24.  
  25. (define q (make-queue 3))
  26. (q 'enqueue 1)
  27. (q 'enqueue 2)
  28. (q 'enqueue 3)
  29. (display (q 'dequeue)) (newline)
  30. (display (q 'dequeue)) (newline)
  31. (display (q 'dequeue)) (newline)
  32. (display (q 'empty?)) (newline)
  33.  
  34. (define (make-queue)
  35.   (let ((q (cons (list) (list)))) ; front/back
  36.     (lambda (command . args)
  37.       (case command
  38.       ((empty?)
  39.         (and (null? (car q)) (null? (cdr q))))
  40.       ((enqueue)
  41.         (set-cdr! q (cons (car args) (cdr q))))
  42.       ((dequeue)
  43.         (cond ((pair? (car q))
  44.                 (let ((x (caar q)))
  45.                   (set-car! q (cdar q))
  46.                   x))
  47.         (else (set-car! q (reverse (cdr q)))
  48.               (set-cdr! q (list))
  49.               (if (null? (car q))
  50.                   (error 'dequeue "Empty")
  51.                   (let ((x (caar q)))
  52.                     (set-car! q (cdar q))
  53.                     x)))))))))
  54.  
  55. (set! q (make-queue))
  56. (display (q 'empty?)) (newline)
  57. (q 'enqueue 1)
  58. (q 'enqueue 2)
  59. (display (q 'empty?)) (newline)
  60. (display (q 'dequeue)) (newline)
  61. (q 'enqueue 3)
  62. (q 'enqueue 4)
  63. (display (q 'dequeue)) (newline)
  64. (display (q 'dequeue)) (newline)
  65. (display (q 'dequeue)) (newline)
Success #stdin #stdout 0.02s 8800KB
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https://ideone.com/uEPCIJ
language:
Scheme (guile 2.2.4)
created:
7 years ago
visibility:
public

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