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1 ;;; assoc.el --- insert/delete/sort functions on association lists
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3 ;; Copyright (C) 1996 Free Software Foundation, Inc.
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5 ;; Author: Barry A. Warsaw <bwarsaw@cen.com>
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6 ;; Keywords: extensions
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7
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8 ;; This file is part of XEmacs.
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9
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10 ;; XEmacs is free software; you can redistribute it and/or modify
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11 ;; it under the terms of the GNU General Public License as published by
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12 ;; the Free Software Foundation; either version 2, or (at your option)
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13 ;; any later version.
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14
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15 ;; XEmacs is distributed in the hope that it will be useful, but
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16 ;; WITHOUT ANY WARRANTY; without even the implied warranty of
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17 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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18 ;; General Public License for more details.
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19
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20 ;; You should have received a copy of the GNU General Public License
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21 ;; along with XEmacs; see the file COPYING. If not, write to the Free
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22 ;; Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
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23 ;; 02111-1307, USA.
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24
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25 ;;; Synched up with: FSF 19.34.
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26
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27 ;;; Commentary:
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28
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29 ;; Association list utilities providing insertion, deletion, sorting
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30 ;; fetching off key-value pairs in association lists.
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31
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32 ;;; Code:
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33
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34 (defun asort (alist-symbol key)
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35 "Move a specified key-value pair to the head of an alist.
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36 The alist is referenced by ALIST-SYMBOL. Key-value pair to move to
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37 head is one matching KEY. Returns the sorted list and doesn't affect
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38 the order of any other key-value pair. Side effect sets alist to new
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39 sorted list."
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40 (set alist-symbol
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41 (sort (copy-alist (eval alist-symbol))
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42 (function (lambda (a b) (equal (car a) key))))))
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43
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44
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45 (defun aelement (key value)
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46 "Makes a list of a cons cell containing car of KEY and cdr of VALUE.
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47 The returned list is suitable as an element of an alist."
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48 (list (cons key value)))
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49
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50
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51 (defun aheadsym (alist)
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52 "Return the key symbol at the head of ALIST."
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53 (car (car alist)))
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54
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55
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56 (defun anot-head-p (alist key)
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57 "Find out if a specified key-value pair is not at the head of an alist.
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58 The alist to check is specified by ALIST and the key-value pair is the
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59 one matching the supplied KEY. Returns nil if ALIST is nil, or if
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60 key-value pair is at the head of the alist. Returns t if key-value
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61 pair is not at the head of alist. ALIST is not altered."
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62 (not (equal (aheadsym alist) key)))
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63
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64
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65 (defun aput (alist-symbol key &optional value)
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66 "Inserts a key-value pair into an alist.
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67 The alist is referenced by ALIST-SYMBOL. The key-value pair is made
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68 from KEY and optionally, VALUE. Returns the altered alist or nil if
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69 ALIST is nil.
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70
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71 If the key-value pair referenced by KEY can be found in the alist, and
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72 VALUE is supplied non-nil, then the value of KEY will be set to VALUE.
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73 If VALUE is not supplied, or is nil, the key-value pair will not be
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74 modified, but will be moved to the head of the alist. If the key-value
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75 pair cannot be found in the alist, it will be inserted into the head
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76 of the alist (with value nil if VALUE is nil or not supplied)."
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77 (let ((elem (aelement key value))
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78 alist)
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79 (asort alist-symbol key)
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80 (setq alist (eval alist-symbol))
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81 (cond ((null alist) (set alist-symbol elem))
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82 ((anot-head-p alist key) (set alist-symbol (nconc elem alist)))
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83 (value (setcar alist (car elem)))
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84 (t alist))))
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85
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86
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87 (defun adelete (alist-symbol key)
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88 "Delete a key-value pair from the alist.
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89 Alist is referenced by ALIST-SYMBOL and the key-value pair to remove
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90 is pair matching KEY. Returns the altered alist."
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91 (asort alist-symbol key)
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92 (let ((alist (eval alist-symbol)))
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93 (cond ((null alist) nil)
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94 ((anot-head-p alist key) alist)
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95 (t (set alist-symbol (cdr alist))))))
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96
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97
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98 (defun aget (alist key &optional keynil-p)
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99 "Returns the value in ALIST that is associated with KEY.
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100 Optional KEYNIL-P describes what to do if the value associated with
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101 KEY is nil. If KEYNIL-P is not supplied or is nil, and the value is
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102 nil, then KEY is returned. If KEYNIL-P is non-nil, then nil would be
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103 returned.
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104
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105 If no key-value pair matching KEY could be found in ALIST, or ALIST is
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106 nil then nil is returned. ALIST is not altered."
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107 (let ((copy (copy-alist alist)))
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108 (cond ((null alist) nil)
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109 ((progn (asort 'copy key)
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110 (anot-head-p copy key)) nil)
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111 ((cdr (car copy)))
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112 (keynil-p nil)
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113 ((car (car copy)))
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114 (t nil))))
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115
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116
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117 (defun amake (alist-symbol keylist &optional valuelist)
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118 "Make an association list.
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119 The association list is attached to the alist referenced by
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120 ALIST-SYMBOL. Each element in the KEYLIST becomes a key and is
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121 associated with the value in VALUELIST with the same index. If
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122 VALUELIST is not supplied or is nil, then each key in KEYLIST is
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123 associated with nil.
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124
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125 KEYLIST and VALUELIST should have the same number of elements, but
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126 this isn't enforced. If VALUELIST is smaller than KEYLIST, remaining
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127 keys are associated with nil. If VALUELIST is larger than KEYLIST,
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128 extra values are ignored. Returns the created alist."
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129 (let ((keycar (car keylist))
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130 (keycdr (cdr keylist))
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131 (valcar (car valuelist))
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132 (valcdr (cdr valuelist)))
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133 (cond ((null keycdr)
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134 (aput alist-symbol keycar valcar))
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135 (t
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136 (amake alist-symbol keycdr valcdr)
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137 (aput alist-symbol keycar valcar))))
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138 (eval alist-symbol))
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139
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140 (provide 'assoc)
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141
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142 ;;; assoc.el ends here
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