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1 ;;;; $Id: queue-m.el,v 1.1 1997/12/02 08:48:36 steve Exp $
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2 ;;;; This file implements a simple FIFO queue using macros.
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3
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4 ;; Copyright (C) 1991-1995 Free Software Foundation
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5
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6 ;; Author: Inge Wallin <inge@lysator.liu.se>
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7 ;; Maintainer: elib-maintainers@lysator.liu.se
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8 ;; Created: before 12 May 1991
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9 ;; Last Modified: $Date: 1997/12/02 08:48:36 $
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10 ;; Keywords: extensions, lisp
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11
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12 ;;;;
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13 ;;;; This file is part of the GNU Emacs lisp library, Elib.
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14 ;;;;
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15 ;;;; GNU Elib is free software; you can redistribute it and/or modify
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16 ;;;; it under the terms of the GNU General Public License as published by
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17 ;;;; the Free Software Foundation; either version 2, or (at your option)
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18 ;;;; any later version.
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19 ;;;;
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20 ;;;; GNU Elib is distributed in the hope that it will be useful,
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21 ;;;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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22 ;;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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23 ;;;; GNU General Public License for more details.
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24 ;;;;
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25 ;;;; You should have received a copy of the GNU General Public License
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26 ;;;; along with GNU Elib; see the file COPYING. If not, write to
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27 ;;;; the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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28 ;;;; Boston, MA 02111-1307, USA
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29 ;;;;
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30 ;;;; Author: Inge Wallin
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31 ;;;;
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32
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33 ;;; Commentary:
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34
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35 ;;; The queue is implemented as a two cons cell list, the first
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36 ;;; containing the tag 'QUEUE. The car of the the second cons
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37 ;;; cell points at the first element of the queue and the cdr points
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38 ;;; at the last. All entries and removals are done using destructive
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39 ;;; functions.
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40 ;;;
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41 ;;; This file implements the short functions as macros for speed in
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42 ;;; compiled code.
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43 ;;;
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44
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45
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46 ;;; Code:
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47
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48 ;; Provide the function version and remove the macro version
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49 (provide 'queue-m)
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50 (setq features (delq 'queue-f features))
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51
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52
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53 ;;; ================================================================
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54
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55
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56 (defmacro queue-create ()
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57 "Create an empty fifo queue."
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58 (` (cons 'QUEUE (cons nil nil))))
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59
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60
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61 (defmacro queue-p (queue)
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62 "Return t if QUEUE is a queue, otherwise return nil."
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63 (` (eq (car-safe (, queue)) 'QUEUE)))
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64
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65
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66 (defun queue-enqueue (queue element)
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67 "Enter an element into a queue.
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68 Args: QUEUE ELEMENT"
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69 (let ((elementcell (cons element nil)))
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70 (if (null (car (cdr queue)))
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71 ;; QUEUE is empty
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72 (setcar (cdr queue)
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73 (setcdr (cdr queue)
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74 elementcell))
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75 (setcdr (cdr (cdr queue))
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76 elementcell)
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77 (setcdr (cdr queue)
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78 elementcell))))
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79
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80
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81 (defun queue-dequeue (queue)
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82 "Remove the first element of QUEUE and return it.
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83 If QUEUE is empty, return nil and do nothing."
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84 (if (car (cdr queue))
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85 (prog1
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86 (car (car (cdr queue)))
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87 (setcar (cdr queue)
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88 (cdr (car (cdr queue))))
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89 (if (null (car (cdr queue)))
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90 (setcdr (cdr queue) nil)))))
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91
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92
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93 (defmacro queue-empty (queue)
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94 "Return t if QUEUE is empty, otherwise return nil."
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95 (` (null (car (cdr (, queue))))))
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96
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97
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98 (defmacro queue-first (queue)
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99 "Return the first element of QUEUE or nil if it is empty.
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100 The element is not removed."
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101 (` (car-safe (car (cdr (, queue))))))
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102
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103
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104 (defmacro queue-nth (queue n)
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105 "Return the nth element of a queue, but don't remove it.
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106 Args: QUEUE N
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107 If the length of the queue is less than N, return nil.
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108
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109 The oldest element (the first one) has number 0."
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110 (` (nth (, n) (car (cdr (, queue))))))
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111
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112
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113 (defmacro queue-last (queue)
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114 "Return the last element of QUEUE or nil if it is empty."
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115 (` (car-safe (cdr (cdr (, queue))))))
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116
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117
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118 (defmacro queue-all (queue)
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119 "Return a list of all elements of QUEUE or nil if it is empty.
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120 The oldest element in the queue is the first in the list."
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121 (` (car (cdr (, queue)))))
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122
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123
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124 (defun queue-copy (queue)
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125 "Return a copy of QUEUE. All entries in QUEUE are also copied."
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126 (let* ((first (copy-sequence (car (cdr queue))))
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127 (last first))
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128 (while (cdr last)
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129 (setq last (cdr last)))
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130 (cons 'QUEUE (cons first last))))
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131
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132
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133 (defmacro queue-length (queue)
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134 "Return the number of elements in QUEUE."
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135 (` (length (car (cdr (, queue))))))
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136
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137
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138 (defmacro queue-clear (queue)
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139 "Remove all elements from QUEUE."
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140 (` (setcdr (, queue) (cons nil nil))))
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141
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142 ;;; queue-m.el ends here
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