--- /dev/null
+;;; regexp-opt.el --- generate efficient regexps to match strings.
+
+;; Copyright (C) 1994, 1995, 1996, 1997 Free Software Foundation, Inc.
+
+;; Author: Simon Marshall <simon@gnu.ai.mit.edu>
+;; Keywords: strings, regexps
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 2, or (at your option)
+;; any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs; see the file COPYING. If not, write to the
+;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+;; Boston, MA 02111-1307, USA.
+
+;;; Commentary:
+
+;; The "opt" in "regexp-opt" stands for "optim\\(al\\|i\\(se\\|ze\\)\\)".
+;;
+;; This package generates a regexp from a given list of strings (which matches
+;; one of those strings) so that the regexp generated by:
+;;
+;; (regexp-opt strings)
+;;
+;; is equivalent to, but more efficient than, the regexp generated by:
+;;
+;; (mapconcat 'regexp-quote strings "\\|")
+;;
+;; For example:
+;;
+;; (let ((strings '("cond" "if" "when" "unless" "while"
+;; "let" "let*" "progn" "prog1" "prog2"
+;; "save-restriction" "save-excursion" "save-window-excursion"
+;; "save-current-buffer" "save-match-data"
+;; "catch" "throw" "unwind-protect" "condition-case")))
+;; (concat "(" (regexp-opt strings t) "\\>"))
+;; => "(\\(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\\)\\)\\>"
+;;
+;; Searching using the above example `regexp-opt' regexp takes approximately
+;; two-thirds of the time taken using the equivalent `mapconcat' regexp.
+
+;; Since this package was written to produce efficient regexps, not regexps
+;; efficiently, it is probably not a good idea to in-line too many calls in
+;; your code, unless you use the following trick with `eval-when-compile':
+;;
+;; (defvar definition-regexp
+;; (eval-when-compile
+;; (concat "^("
+;; (regexp-opt '("defun" "defsubst" "defmacro" "defalias"
+;; "defvar" "defconst") t)
+;; "\\>")))
+;;
+;; The `byte-compile' code will be as if you had defined the variable thus:
+;;
+;; (defvar definition-regexp
+;; "^(\\(def\\(alias\\|const\\|macro\\|subst\\|un\\|var\\)\\)\\>")
+;;
+;; Note that if you use this trick for all instances of `regexp-opt' and
+;; `regexp-opt-depth' in your code, regexp-opt.el would only have to be loaded
+;; at compile time. But note also that using this trick means that should
+;; regexp-opt.el be changed, perhaps to fix a bug or to add a feature to
+;; improve the efficiency of `regexp-opt' regexps, you would have to recompile
+;; your code for such changes to have effect in your code.
+
+;; Originally written for font-lock.el, from an idea from Stig's hl319.el, with
+;; thanks for ideas also to Michael Ernst, Bob Glickstein and Dan Nicolaescu.
+;; Please don't tell me that it doesn't produce optimal regexps; I know that
+;; already. For example, the above explanation for the meaning of "opt" would
+;; be more efficient as "optim\\(al\\|i[sz]e\\)", but this requires complex
+;; forward looking. But (ideas or) code to improve things (are) is welcome.
+\f
+;;; Code:
+
+;;;###autoload
+(defun regexp-opt (strings &optional paren)
+ "Return a regexp to match a string in STRINGS.
+Each string should be unique in STRINGS and should not contain any regexps,
+quoted or not. If optional PAREN is non-nil, ensure that the returned regexp
+is enclosed by at least one regexp grouping construct.
+The returned regexp is typically more efficient than the equivalent regexp:
+
+ (let ((open-paren (if PAREN \"\\\\(\" \"\")) (close-paren (if PAREN \"\\\\)\" \"\")))
+ (concat open-paren (mapconcat 'regexp-quote STRINGS \"\\\\|\") close-paren))
+
+but typically contains more regexp grouping constructs.
+Use `regexp-opt-depth' to count them."
+ (save-match-data
+ ;; Recurse on the sorted list.
+ (let ((max-lisp-eval-depth (* 1024 1024))
+ (completion-ignore-case nil))
+ (regexp-opt-group (sort (copy-sequence strings) 'string-lessp) paren))))
+
+;;;###autoload
+(defun regexp-opt-depth (regexp)
+ "Return the depth of REGEXP.
+This means the number of regexp grouping constructs (parenthesised expressions)
+in REGEXP."
+ (save-match-data
+ ;; Hack to signal an error if REGEXP does not have balanced parentheses.
+ (string-match regexp "")
+ ;; Count the number of open parentheses in REGEXP.
+ (let ((count 0) start)
+ (while (string-match "\\\\(" regexp start)
+ (setq count (1+ count) start (match-end 0)))
+ count)))
+\f
+;;; Workhorse functions.
+
+(eval-when-compile
+ (require 'cl))
+
+(unless (fboundp 'make-bool-vector)
+ (defalias 'make-bool-vector 'make-vector))
+
+(defun regexp-opt-group (strings &optional paren lax)
+ ;;
+ ;; Return a regexp to match a string in STRINGS.
+ ;; If PAREN non-nil, output regexp parentheses around returned regexp.
+ ;; If LAX non-nil, don't output parentheses if it doesn't require them.
+ ;; Merges keywords to avoid backtracking in Emacs' regexp matcher.
+ ;;
+ ;; The basic idea is to find the shortest common prefix, remove it and
+ ;; recurse. If there is no prefix, we divide the list into two so that (at
+ ;; least) one half will have at least a one-character common prefix.
+ ;;
+ ;; Also we delay the addition of grouping parenthesis as long as possible
+ ;; until we're sure we need them, and try to remove one-character sequences
+ ;; so we can use character sets rather than grouping parenthesis.
+ ;;
+ (let* ((open-group (if paren "\\(" ""))
+ (close-group (if paren "\\)" ""))
+ (open-charset (if lax "" open-group))
+ (close-charset (if lax "" close-group)))
+ (cond
+ ;;
+ ;; If there is only one string, just return it.
+ ((= (length strings) 1)
+ (if (= (length (car strings)) 1)
+ (concat open-charset (regexp-quote (car strings)) close-charset)
+ (concat open-group (regexp-quote (car strings)) close-group)))
+ ;;
+ ;; If there is an empty string, remove it and recurse on the rest.
+ ((= (length (car strings)) 0)
+ (concat open-charset
+ (regexp-opt-group (cdr strings) t t) "?"
+ close-charset))
+ ;;
+ ;; If all are one-character strings, just return a character set.
+ ((= (length strings) (apply '+ (mapcar 'length strings)))
+ (concat open-charset
+ (regexp-opt-charset strings)
+ close-charset))
+ ;;
+ ;; We have a list of different length strings.
+ (t
+ (let ((prefix (try-completion "" (mapcar 'list strings)))
+ (letters (let ((completion-regexp-list '("^.$")))
+ (all-completions "" (mapcar 'list strings)))))
+ (cond
+ ;;
+ ;; If there is a common prefix, remove it and recurse on the suffixes.
+ ((> (length prefix) 0)
+ (let* ((length (length prefix))
+ (suffixes (mapcar (lambda (s) (substring s length)) strings)))
+ (concat open-group
+ (regexp-quote prefix) (regexp-opt-group suffixes t t)
+ close-group)))
+ ;;
+ ;; If there are several one-character strings, remove them and recurse
+ ;; on the rest (first so the final regexp finds the longest match).
+ ((> (length letters) 1)
+ (let ((rest (let ((completion-regexp-list '("^..+$")))
+ (all-completions "" (mapcar 'list strings)))))
+ (concat open-group
+ (regexp-opt-group rest) "\\|" (regexp-opt-charset letters)
+ close-group)))
+ ;;
+ ;; Otherwise, divide the list into those that start with a particular
+ ;; letter and those that do not, and recurse on them.
+ (t
+ (let* ((char (substring (car strings) 0 1))
+ (half1 (all-completions char (mapcar 'list strings)))
+ (half2 (nthcdr (length half1) strings)))
+ (concat open-group
+ (regexp-opt-group half1) "\\|" (regexp-opt-group half2)
+ close-group)))))))))
+
+(defun regexp-opt-charset (chars)
+ ;;
+ ;; Return a regexp to match a character in CHARS.
+ ;;
+ ;; The basic idea is to find character ranges. Also we take care in the
+ ;; position of character set meta characters in the character set regexp.
+ ;;
+ (let* ((charwidth 256) ; Yeah, right.
+ (charmap (make-bool-vector charwidth nil))
+ (charset "")
+ (bracket "") (dash "") (caret ""))
+ ;;
+ ;; Make a character map but extract character set meta characters.
+ (dolist (char (mapcar 'string-to-char chars))
+ (case char
+ (?\]
+ (setq bracket "]"))
+ (?^
+ (setq caret "^"))
+ (?-
+ (setq dash "-"))
+ (otherwise
+ (aset charmap char t))))
+ ;;
+ ;; Make a character set from the map using ranges where applicable.
+ (dotimes (char charwidth)
+ (let ((start char))
+ (while (and (< char charwidth) (aref charmap char))
+ (incf char))
+ (cond ((> char (+ start 3))
+ (setq charset (format "%s%c-%c" charset start (1- char))))
+ ((> char start)
+ (setq charset (format "%s%c" charset (setq char start)))))))
+ ;;
+ ;; Make sure a caret is not first and a dash is first or last.
+ (if (and (string-equal charset "") (string-equal bracket ""))
+ (concat "[" dash caret "]")
+ (concat "[" bracket charset caret dash "]"))))
+
+(provide 'regexp-opt)
+
+;;; regexp-opt.el ends here
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