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1 ;;; assoc.el --- insert/delete/sort functions on association lists
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2
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3 ;; Author: Barry A. Warsaw <bwarsaw@cen.com>
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4 ;; Keywords: extensions
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5
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6 ;; This software is distributed in the hope that it will be useful,
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7 ;; but WITHOUT ANY WARRANTY. No author or distributor accepts
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8 ;; responsibility to anyone for the consequences of using it or for
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9 ;; whether it serves any particular purpose or works at all, unless he
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10 ;; says so in writing.
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11
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12 ;; This software was written as part of the supercite author's
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13 ;; official duty as an employee of the United States Government and is
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14 ;; thus in the public domain. You are free to use that particular
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15 ;; software as you wish, but WITHOUT ANY WARRANTY WHATSOEVER. It
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16 ;; would be nice, though if when you use any of this code, you give
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17 ;; due credit to the author.
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18
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19 ;;; Synched up with: FSF 19.30.
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20
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21 ;;; Commentary:
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22
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23 ;; Association list utilities providing insertion, deletion, sorting
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24 ;; fetching off key-value pairs in association lists.
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25
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26 ;;; Code:
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27
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28 (defun asort (alist-symbol key)
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29 "Move a specified key-value pair to the head of an alist.
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30 The alist is referenced by ALIST-SYMBOL. Key-value pair to move to
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31 head is one matching KEY. Returns the sorted list and doesn't affect
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32 the order of any other key-value pair. Side effect sets alist to new
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33 sorted list."
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34 (set alist-symbol
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35 (sort (copy-alist (eval alist-symbol))
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36 (function (lambda (a b) (equal (car a) key))))))
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37
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38
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39 (defun aelement (key value)
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40 "Makes a list of a cons cell containing car of KEY and cdr of VALUE.
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41 The returned list is suitable as an element of an alist."
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42 (list (cons key value)))
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43
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44
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45 (defun aheadsym (alist)
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46 "Return the key symbol at the head of ALIST."
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47 (car (car alist)))
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48
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49
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50 (defun anot-head-p (alist key)
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51 "Find out if a specified key-value pair is not at the head of an alist.
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52 The alist to check is specified by ALIST and the key-value pair is the
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53 one matching the supplied KEY. Returns nil if ALIST is nil, or if
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54 key-value pair is at the head of the alist. Returns t if key-value
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55 pair is not at the head of alist. ALIST is not altered."
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56 (not (equal (aheadsym alist) key)))
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57
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58
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59 (defun aput (alist-symbol key &optional value)
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60 "Inserts a key-value pair into an alist.
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61 The alist is referenced by ALIST-SYMBOL. The key-value pair is made
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62 from KEY and optionally, VALUE. Returns the altered alist or nil if
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63 ALIST is nil.
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64
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65 If the key-value pair referenced by KEY can be found in the alist, and
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66 VALUE is supplied non-nil, then the value of KEY will be set to VALUE.
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67 If VALUE is not supplied, or is nil, the key-value pair will not be
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68 modified, but will be moved to the head of the alist. If the key-value
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69 pair cannot be found in the alist, it will be inserted into the head
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70 of the alist (with value nil if VALUE is nil or not supplied)."
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71 (let ((elem (aelement key value))
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72 alist)
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73 (asort alist-symbol key)
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74 (setq alist (eval alist-symbol))
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75 (cond ((null alist) (set alist-symbol elem))
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76 ((anot-head-p alist key) (set alist-symbol (nconc elem alist)))
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77 (value (setcar alist (car elem)))
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78 (t alist))))
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79
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80
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81 (defun adelete (alist-symbol key)
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82 "Delete a key-value pair from the alist.
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83 Alist is referenced by ALIST-SYMBOL and the key-value pair to remove
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84 is pair matching KEY. Returns the altered alist."
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85 (asort alist-symbol key)
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86 (let ((alist (eval alist-symbol)))
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87 (cond ((null alist) nil)
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88 ((anot-head-p alist key) alist)
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89 (t (set alist-symbol (cdr alist))))))
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90
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91
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92 (defun aget (alist key &optional keynil-p)
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93 "Returns the value in ALIST that is associated with KEY.
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94 Optional KEYNIL-P describes what to do if the value associated with
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95 KEY is nil. If KEYNIL-P is not supplied or is nil, and the value is
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96 nil, then KEY is returned. If KEYNIL-P is non-nil, then nil would be
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97 returned.
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98
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99 If no key-value pair matching KEY could be found in ALIST, or ALIST is
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100 nil then nil is returned. ALIST is not altered."
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101 (let ((copy (copy-alist alist)))
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102 (cond ((null alist) nil)
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103 ((progn (asort 'copy key)
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104 (anot-head-p copy key)) nil)
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105 ((cdr (car copy)))
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106 (keynil-p nil)
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107 ((car (car copy)))
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108 (t nil))))
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109
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110
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111 (defun amake (alist-symbol keylist &optional valuelist)
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112 "Make an association list.
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113 The association list is attached to the alist referenced by
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114 ALIST-SYMBOL. Each element in the KEYLIST becomes a key and is
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115 associated with the value in VALUELIST with the same index. If
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116 VALUELIST is not supplied or is nil, then each key in KEYLIST is
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117 associated with nil.
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118
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119 KEYLIST and VALUELIST should have the same number of elements, but
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120 this isn't enforced. If VALUELIST is smaller than KEYLIST, remaining
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121 keys are associated with nil. If VALUELIST is larger than KEYLIST,
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122 extra values are ignored. Returns the created alist."
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123 (let ((keycar (car keylist))
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124 (keycdr (cdr keylist))
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125 (valcar (car valuelist))
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126 (valcdr (cdr valuelist)))
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127 (cond ((null keycdr)
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128 (aput alist-symbol keycar valcar))
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129 (t
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130 (amake alist-symbol keycdr valcdr)
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131 (aput alist-symbol keycar valcar))))
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132 (eval alist-symbol))
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133
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134 (provide 'assoc)
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135
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136 ;;; assoc.el ends here
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