Initial revision

lisp/paren.el

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+;;; paren.el --- highlight matching paren.
+;; Copyright (C) 1993 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 blink-paren-overlay nil)
+
+;; Find the place to blink, if there is one,
+;; and blink it until input arrives.
+(defun blink-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 blink.
+	(if mismatch
+	    (setq pos nil))))
+    (cond (pos
+	   (if blink-paren-overlay
+	       (move-overlay blink-paren-overlay (- pos dir) pos)
+	     (setq blink-paren-overlay
+		   (make-overlay (- pos dir) pos)))
+	   (overlay-put blink-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 blink-paren-overlay
+;;;			  'face
+;;;			  (if (overlay-get blink-paren-overlay
+;;;					   'face)
+;;;			      nil face)))
+	   )
+	  (t
+	   (delete-overlay blink-paren-overlay)))))
+
+(add-hook 'post-command-hook 'blink-paren-command-hook)
+