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1 ;;; regexp-opt.el --- generate efficient regexps to match strings.
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2
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3 ;; Copyright (C) 1994, 1995, 1996, 1997 Free Software Foundation, Inc.
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4
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5 ;; Author: Simon Marshall <simon@gnu.ai.mit.edu>
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6 ;; Keywords: strings, regexps
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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,
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16 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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17 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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18 ;; GNU 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
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22 ;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
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23 ;; Boston, MA 02111-1307, USA.
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24
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25 ;;; Commentary:
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26
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27 ;; The "opt" in "regexp-opt" stands for "optim\\(al\\|i\\(se\\|ze\\)\\)".
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28 ;;
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29 ;; This package generates a regexp from a given list of strings (which matches
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30 ;; one of those strings) so that the regexp generated by:
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31 ;;
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32 ;; (regexp-opt strings)
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33 ;;
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34 ;; is equivalent to, but more efficient than, the regexp generated by:
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35 ;;
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36 ;; (mapconcat 'regexp-quote strings "\\|")
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37 ;;
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38 ;; For example:
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39 ;;
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40 ;; (let ((strings '("cond" "if" "when" "unless" "while"
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41 ;; "let" "let*" "progn" "prog1" "prog2"
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42 ;; "save-restriction" "save-excursion" "save-window-excursion"
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43 ;; "save-current-buffer" "save-match-data"
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44 ;; "catch" "throw" "unwind-protect" "condition-case")))
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45 ;; (concat "(" (regexp-opt strings t) "\\>"))
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46 ;; => "(\\(c\\(atch\\|ond\\(ition-case\\)?\\)\\|if\\|let\\*?\\|prog[12n]\\|save-\\(current-buffer\\|excursion\\|match-data\\|restriction\\|window-excursion\\)\\|throw\\|un\\(less\\|wind-protect\\)\\|wh\\(en\\|ile\\)\\)\\>"
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47 ;;
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48 ;; Searching using the above example `regexp-opt' regexp takes approximately
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49 ;; two-thirds of the time taken using the equivalent `mapconcat' regexp.
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50
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51 ;; Since this package was written to produce efficient regexps, not regexps
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52 ;; efficiently, it is probably not a good idea to in-line too many calls in
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53 ;; your code, unless you use the following trick with `eval-when-compile':
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54 ;;
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55 ;; (defvar definition-regexp
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56 ;; (eval-when-compile
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57 ;; (concat "^("
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58 ;; (regexp-opt '("defun" "defsubst" "defmacro" "defalias"
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59 ;; "defvar" "defconst") t)
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60 ;; "\\>")))
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61 ;;
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62 ;; The `byte-compile' code will be as if you had defined the variable thus:
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63 ;;
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64 ;; (defvar definition-regexp
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65 ;; "^(\\(def\\(alias\\|const\\|macro\\|subst\\|un\\|var\\)\\)\\>")
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66 ;;
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67 ;; Note that if you use this trick for all instances of `regexp-opt' and
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68 ;; `regexp-opt-depth' in your code, regexp-opt.el would only have to be loaded
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69 ;; at compile time. But note also that using this trick means that should
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70 ;; regexp-opt.el be changed, perhaps to fix a bug or to add a feature to
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71 ;; improve the efficiency of `regexp-opt' regexps, you would have to recompile
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72 ;; your code for such changes to have effect in your code.
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73
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74 ;; Originally written for font-lock.el, from an idea from Stig's hl319.el, with
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75 ;; thanks for ideas also to Michael Ernst, Bob Glickstein and Dan Nicolaescu.
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76 ;; Please don't tell me that it doesn't produce optimal regexps; I know that
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77 ;; already. For example, the above explanation for the meaning of "opt" would
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78 ;; be more efficient as "optim\\(al\\|i[sz]e\\)", but this requires complex
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79 ;; forward looking. But (ideas or) code to improve things (are) is welcome.
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80
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81 ;;; Code:
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82
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83 ;;;###autoload
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84 (defun regexp-opt (strings &optional paren)
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85 "Return a regexp to match a string in STRINGS.
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86 Each string should be unique in STRINGS and should not contain any regexps,
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87 quoted or not. If optional PAREN is non-nil, ensure that the returned regexp
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88 is enclosed by at least one regexp grouping construct.
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89 The returned regexp is typically more efficient than the equivalent regexp:
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90
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91 (let ((open-paren (if PAREN \"\\\\(\" \"\")) (close-paren (if PAREN \"\\\\)\" \"\")))
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92 (concat open-paren (mapconcat 'regexp-quote STRINGS \"\\\\|\") close-paren))
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93
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94 but typically contains more regexp grouping constructs.
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95 Use `regexp-opt-depth' to count them."
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96 (save-match-data
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97 ;; Recurse on the sorted list.
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98 (let ((max-lisp-eval-depth (* 1024 1024))
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99 (completion-ignore-case nil))
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100 (regexp-opt-group (sort (copy-sequence strings) 'string-lessp) paren))))
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101
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102 ;;;###autoload
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103 (defun regexp-opt-depth (regexp)
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104 "Return the depth of REGEXP.
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105 This means the number of regexp grouping constructs (parenthesised expressions)
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106 in REGEXP."
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107 (save-match-data
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108 ;; Hack to signal an error if REGEXP does not have balanced parentheses.
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109 (string-match regexp "")
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110 ;; Count the number of open parentheses in REGEXP.
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111 (let ((count 0) start)
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112 (while (string-match "\\\\(" regexp start)
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113 (setq count (1+ count) start (match-end 0)))
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114 count)))
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115
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116 ;;; Workhorse functions.
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117
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118 (eval-when-compile
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119 (require 'cl))
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120
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121 (unless (fboundp 'make-bool-vector)
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122 (defalias 'make-bool-vector 'make-vector))
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123
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124 (defun regexp-opt-group (strings &optional paren lax)
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125 ;;
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126 ;; Return a regexp to match a string in STRINGS.
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127 ;; If PAREN non-nil, output regexp parentheses around returned regexp.
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128 ;; If LAX non-nil, don't output parentheses if it doesn't require them.
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129 ;; Merges keywords to avoid backtracking in Emacs' regexp matcher.
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130 ;;
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131 ;; The basic idea is to find the shortest common prefix, remove it and
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132 ;; recurse. If there is no prefix, we divide the list into two so that (at
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133 ;; least) one half will have at least a one-character common prefix.
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134 ;;
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135 ;; Also we delay the addition of grouping parenthesis as long as possible
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136 ;; until we're sure we need them, and try to remove one-character sequences
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137 ;; so we can use character sets rather than grouping parenthesis.
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138 ;;
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139 (let* ((open-group (if paren "\\(" ""))
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140 (close-group (if paren "\\)" ""))
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141 (open-charset (if lax "" open-group))
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142 (close-charset (if lax "" close-group)))
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143 (cond
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144 ;;
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145 ;; If there is only one string, just return it.
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146 ((= (length strings) 1)
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147 (if (= (length (car strings)) 1)
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148 (concat open-charset (regexp-quote (car strings)) close-charset)
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149 (concat open-group (regexp-quote (car strings)) close-group)))
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150 ;;
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151 ;; If there is an empty string, remove it and recurse on the rest.
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152 ((= (length (car strings)) 0)
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153 (concat open-charset
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154 (regexp-opt-group (cdr strings) t t) "?"
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155 close-charset))
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156 ;;
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157 ;; If all are one-character strings, just return a character set.
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158 ((= (length strings) (apply '+ (mapcar 'length strings)))
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159 (concat open-charset
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160 (regexp-opt-charset strings)
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161 close-charset))
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162 ;;
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163 ;; We have a list of different length strings.
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164 (t
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165 (let ((prefix (try-completion "" (mapcar 'list strings)))
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166 (letters (let ((completion-regexp-list '("^.$")))
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167 (all-completions "" (mapcar 'list strings)))))
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168 (cond
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169 ;;
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170 ;; If there is a common prefix, remove it and recurse on the suffixes.
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171 ((> (length prefix) 0)
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172 (let* ((length (length prefix))
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173 (suffixes (mapcar (lambda (s) (substring s length)) strings)))
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174 (concat open-group
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175 (regexp-quote prefix) (regexp-opt-group suffixes t t)
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176 close-group)))
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177 ;;
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178 ;; If there are several one-character strings, remove them and recurse
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179 ;; on the rest (first so the final regexp finds the longest match).
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180 ((> (length letters) 1)
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181 (let ((rest (let ((completion-regexp-list '("^..+$")))
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182 (all-completions "" (mapcar 'list strings)))))
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183 (concat open-group
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184 (regexp-opt-group rest) "\\|" (regexp-opt-charset letters)
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185 close-group)))
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186 ;;
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187 ;; Otherwise, divide the list into those that start with a particular
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188 ;; letter and those that do not, and recurse on them.
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189 (t
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190 (let* ((char (substring (car strings) 0 1))
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191 (half1 (all-completions char (mapcar 'list strings)))
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192 (half2 (nthcdr (length half1) strings)))
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193 (concat open-group
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194 (regexp-opt-group half1) "\\|" (regexp-opt-group half2)
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195 close-group)))))))))
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196
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197 (defun regexp-opt-charset (chars)
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198 ;;
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199 ;; Return a regexp to match a character in CHARS.
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200 ;;
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201 ;; The basic idea is to find character ranges. Also we take care in the
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202 ;; position of character set meta characters in the character set regexp.
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203 ;;
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204 (let* ((charwidth 256) ; Yeah, right.
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205 ;; XEmacs: use bit-vectors instead of bool-vectors
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206 (charmap (make-bit-vector charwidth 0))
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207 (charset "")
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208 (bracket "") (dash "") (caret ""))
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209 ;;
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210 ;; Make a character map but extract character set meta characters.
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211 (dolist (char (mapcar 'string-to-char chars))
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212 (case char
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213 (?\]
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214 (setq bracket "]"))
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215 (?^
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216 (setq caret "^"))
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217 (?-
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218 (setq dash "-"))
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219 (otherwise
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220 ;; XEmacs: 1
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221 (aset charmap char 1))))
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222 ;;
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223 ;; Make a character set from the map using ranges where applicable.
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224 (dotimes (char charwidth)
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225 (let ((start char))
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226 (while (and (< char charwidth)
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227 ;; XEmacs: (not (zerop ...))
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228 (not (zerop (aref charmap char))))
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229 (incf char))
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230 (cond ((> char (+ start 3))
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231 (setq charset (format "%s%c-%c" charset start (1- char))))
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232 ((> char start)
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233 (setq charset (format "%s%c" charset (setq char start)))))))
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234 ;;
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235 ;; Make sure a caret is not first and a dash is first or last.
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236 (if (and (string-equal charset "") (string-equal bracket ""))
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237 (concat "[" dash caret "]")
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238 (concat "[" bracket charset caret dash "]"))))
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239
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240 (provide 'regexp-opt)
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241
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242 ;;; regexp-opt.el ends here
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