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;;; paren.el --- highlight matching paren.
;; Copyright (C) 1993 Free Software Foundation, Inc.
;; 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, 675 Mass Ave, Cambridge, MA 02139, USA.
;;; Commentary:
;; Load this and it will display highlighting on whatever
;; paren matches the one before or after point.
;;; Code:
(defvar show-paren-overlay nil)
;; Find the place to show, if there is one,
;; and show it until input arrives.
(defun show-paren-command-hook ()
(let (pos dir mismatch (oldpos (point))
(face (if (face-equal 'highlight 'region)
'underline 'highlight)))
(cond ((eq (char-syntax (following-char)) ?\()
(setq dir 1))
((eq (char-syntax (preceding-char)) ?\))
(setq dir -1)))
(save-excursion
(save-restriction
;; Determine the range within which to look for a match.
(if blink-matching-paren-distance
(narrow-to-region (max (point-min)
(- (point) blink-matching-paren-distance))
(min (point-max)
(+ (point) blink-matching-paren-distance))))
;; Scan across one sexp within that range.
(condition-case ()
(setq pos (scan-sexps (point) dir))
(error nil))
;; See if the "matching" paren is the right kind of paren
;; to match the one we started at.
(if pos
(let ((beg (min pos oldpos)) (end (max pos oldpos)))
(and (/= (char-syntax (char-after beg)) ?\$)
(setq mismatch
(/= (char-after (1- end))
(logand (lsh (aref (syntax-table)
(char-after beg))
-8)
255))))))
;; If they don't properly match, don't show.
(if mismatch
(setq pos nil))))
(cond (pos
(if show-paren-overlay
(move-overlay show-paren-overlay (- pos dir) pos)
(setq show-paren-overlay
(make-overlay (- pos dir) pos)))
(overlay-put show-paren-overlay 'face face)
;;; This is code to blink the highlighting.
;;; It is desirable to avoid this because
;;; it would interfere with auto-save and gc when idle.
;;; (while (sit-for 1)
;;; (overlay-put show-paren-overlay
;;; 'face
;;; (if (overlay-get show-paren-overlay
;;; 'face)
;;; nil face)))
)
(t
(and show-paren-overlay (overlay-buffer show-paren-overlay)
(delete-overlay show-paren-overlay))))))
(add-hook 'post-command-hook 'show-paren-command-hook)
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