1 ;;; <queue.ss> ---- Excessively simple queue implementation.

2 ;;; Copyright (C) 2004 by Tony Garnock-Jones.

3

4 ;;; This is free software; you can redistribute it and/or

5 ;;; modify it under the terms of the GNU Lesser General Public

6 ;;; License as published by the Free Software Foundation; either

7 ;;; version 2.1 of the License, or (at your option) any later version.

8

9 ;;; This software is distributed in the hope that it will be useful,

10 ;;; but WITHOUT ANY WARRANTY; without even the implied warranty of

11 ;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU

12 ;;; Lesser General Public License for more details.

13

14 ;;; You should have received a copy of the GNU Lesser General Public

15 ;;; License along with this software; if not, write to the Free Software

16 ;;; Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA

17

18 ;;; Author: Tony Garnock-Jones <tonyg@kcbbs.gen.nz>

19

20 (module queue mzscheme

21 (provide make-q enq! deq! q->list list->q q-empty?)

22

23 (define (make-q)

24 (cons '() '()))

25

26 (define (enq! q e)

27 (let ((cell (cons e '())))

28 (if (null? (car q))

29 (set-car! q cell)

30 (set-cdr! (cdr q) cell))

31 (set-cdr! q cell)))

32

33 (define (deq! q)

34 (if (null? (car q))

35 #f

36 (let ((v (caar q)))

37 (set-car! q (cdar q))

38 (if (null? (car q))

39 (set-cdr! q '()))

40 v)))

41

42 (define (q->list q)

43 (car q))

44

45 (define (list->q lst)

46 (let ((q (make-q)))

47 (for-each (lambda (x) (enq! q x)) lst)

48 q))

49

50 (define (q-empty? q)

51 (null? (car q)))

52 )