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;;; master.el --- make a buffer the master over another buffer

;; Copyright (C) 1999, 2000, 2001  Alexander Schroeder

;; Author: Alex Schroeder <alex@gnu.org>
;; Maintainer: Alex Schroeder <alex@gnu.org>
;; Version: 1.0.2
;; Keywords: comm

;; 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:

;; master-mode is a minor mode which enables you to scroll another
;; buffer (the slave) without leaving your current buffer (the master).

;; It can be used by sql.el, for example: The SQL buffer is the master
;; and its SQLi buffer is the slave.  This allows you to scroll the SQLi
;; buffer containing the output from the SQL buffer containing the
;; commands.
;;
;; This is how to use sql.el and master.el together: The variable
;; sql-buffer contains the slave buffer.  It is a local variable in the
;; SQL buffer.
;;
;; (add-hook 'sql-mode-hook
;;	   (function (lambda ()
;;		       (master-mode t)
;;		       (master-set-slave sql-buffer))))
;; (add-hook 'sql-set-sqli-hook
;;	   (function (lambda ()
;;		       (master-set-slave sql-buffer))))

;;; Thanks to all the people who helped me out:
;;
;; Rob Riepel <networking.stanford.edu>

;;; History:
;;

;;; Code:

(require 'easy-mmode)

;; Variables that don't need initialization.

(defvar master-of nil
  "Slave buffer of the current buffer.  See `master-mode'.
You can set this variable using `master-set-slave'.")

(defvar master-set-slave-hook nil
  "Hook run after the slave is changed using \\[master-set-slave].")

;;; Define master mode.

;;;###autoload
(define-minor-mode master-mode
  "Toggle Master mode.
With no argument, this command toggles the mode.
Non-null prefix argument turns on the mode.
Null prefix argument turns off the mode.

When Master mode is enabled, you can scroll the slave buffer using the
following commands:

\\{master-mode-map}

The slave buffer is stored in the buffer-local variable `master-of'.
You can set this variable using `master-set-slave'.  You can show
yourself the value of `master-of' by calling `master-show-slave'."
 ;; The initial value.
 nil
 ;; The indicator for the mode line.
 nil
 ;; The minor mode bindings.
 '(("\C-c\C-n" . master-says-scroll-up)
   ("\C-c\C-p" . master-says-scroll-down)
   ("\C-c<" . master-says-beginning-of-buffer)
   ("\C-c>" . master-says-end-of-buffer)
   ("\C-c\C-l" . master-says-recenter)))

;; Initialize Master mode by setting a slave buffer.

(defun master-set-slave (buffer)
  "Makes BUFFER the slave of the current buffer.
Use \\[master-mode] to toggle control of the slave buffer."
  (interactive "bSlave: ")
  (make-local-variable 'master-of)
  (setq master-of buffer)
  (run-hooks 'master-set-slave-hook))

(defun master-show-slave ()
  "Displays a message with the name of the slave buffer."
  (interactive)
  (message "This buffer is the master of %s.  Master-mode is %S."
	   (or master-of "none")
	   master-mode))



;;; Functions that the master buffer can call for the slave buffer.

(defun master-says-scroll-up (&optional arg)
  "Display and scroll the slave buffer up.
See `scroll-up'."
  (interactive)
  (master-says 'scroll-up arg))

(defun master-says-scroll-down (&optional arg)
  "Display and scroll the slave buffer down.
See `scroll-down'."
  (interactive)
  (master-says 'scroll-down arg))

(defun master-says-beginning-of-buffer (&optional arg)
  "Display and move to the beginning of the slave buffer.
See `beginning-of-buffer'."
  (interactive)
  (master-says 'beginning-of-buffer arg))

(defun master-says-end-of-buffer (&optional arg)
  "Display and move to the end of the slave buffer.
See `end-of-buffer'."
  (interactive)
  (master-says 'end-of-buffer arg))

(defun master-says-recenter (&optional arg)
  "Recenter the slave buffer.
See `recenter'."
  (interactive)
  (master-says 'recenter arg))

;; The master function doing the stuff.

(defun master-says (&optional command arg)
  "Display slave buffer and execute COMMAND with ARG in its window."
  (interactive)
  (if (null (buffer-live-p (get-buffer master-of)))
      (error "Slave buffer has disappeared")
    (let ((window  (selected-window)))
      (if (not (eq (window-buffer window) (get-buffer master-of)))
	  (switch-to-buffer-other-window master-of))
      (if command (condition-case nil (apply command arg) (error nil)))
      (select-window window))))

(provide 'master)

;;; master.el ends here