[elpa] externals/quarter-plane 8cf26bf 1/7: New package quarter-plane.

[Stefan Monnier]

branch: externals/quarter-plane
commit 8cf26bf19d0193068bef34dd0103e8a7ea566afa
Author: Peter J. Weisberg <pj@irregularexpressions.net>
Commit: Stefan Monnier <monnier@iro.umontreal.ca>

    New package quarter-plane.
---
 quarter-plane.el | 112 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 112 insertions(+)

diff --git a/quarter-plane.el b/quarter-plane.el
new file mode 100644
index 0000000..dbde423
--- /dev/null
+++ b/quarter-plane.el
@@ -0,0 +1,112 @@
+;;; quarter-plane.el --- editing using quarter-plane screen model
+
+;; Copyright (C) 2011  Free Software Foundation, Inc.
+
+;; Author: Peter J. Weisberg
+;; Version: 0.1
+;; Keywords: convenience wp
+
+;; This program 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 3 of the License, or
+;; (at your option) any later version.
+
+;; This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; This code provides a minor mode to enable the some of picture-mode
+;; commands documented in the Emacs manual in order to treat the
+;; screen as a semi-infinite quarter-plane, without changing the
+;; buffer's major mode.
+
+;; Known issues:
+
+;; Quarter-Plane mode doesn't work in read-only buffers, where it
+;; can't insert spaces.
+
+;; The user doesn't really care about the "modifications" of adding
+;; whitespace that's going to be trimmed when he exits quarter-plane
+;; mode or saves, but it's still part of the undo history.
+
+;; Both of these are due to the disconnect between what the user
+;; really wants--movement of the cursor within the window, regardless
+;; of where the text is--and what the mode can actually do--add dummy
+;; text to give the cursor a place to move to.
+
+;;; Code:
+
+(require 'picture)
+
+(defvar quarter-plane-mode-map
+  (let ((map (make-sparse-keymap)))
+    (define-key map [remap right-char] 'picture-forward-column)
+    (define-key map [remap forward-char] 'picture-forward-column)
+    (define-key map [remap previous-line] 'picture-move-up)
+    (define-key map [remap next-line] 'picture-move-down)
+    (define-key map [remap mouse-set-point] 'picture-mouse-set-point)
+    map))
+
+(defconst quarter-plane-saved-symbols
+  '(truncate-lines show-trailing-whitespace)
+  "Buffer-local variables whose modified by `quarter-plane-mode`.
+Their values are saved when `quarter-plane-mode` is enabled and restored
+when it's disabled.")
+
+(defvar quarter-plane-saved-values)
+(make-variable-buffer-local 'quarter-plane-saved-values)
+(put 'quarter-plane-saved-values 'permanent-local t)
+
+;;;###autoload
+(define-minor-mode quarter-plane-mode
+  "Toggle Quarter-Plane mode on or off.
+Interactively, with no prefix argument, toggle the mode.
+With universal prefix ARG turn mode on.
+With zero or negative ARG turn mode off.
+
+Use point movement commands that act as if the text extended
+infinitely down and to the right, inserting spaces as necessary.
+Excess whitespace is trimmed when saving or exiting Quarter-Plane mode.
+
+Because it works by inserting spaces, Quarter-Plane mode won't work in
+read-only buffers
+
+\\{quarter-plane-mode-map}"
+  :lighter " Plane"
+  :group 'picture
+  :keymap quarter-plane-mode-map
+  (cond
+   (quarter-plane-mode
+    (add-hook 'before-save-hook 'quarter-plane-delete-whitespace nil t)
+    (setq quarter-plane-saved-values nil)
+    (dolist (sym quarter-plane-saved-symbols)
+      (push (symbol-value sym) quarter-plane-saved-values))
+    (setq quarter-plane-saved-values (nreverse quarter-plane-saved-values))
+    (setq truncate-lines t)
+    (setq show-trailing-whitespace nil))
+   (t
+    (remove-hook 'before-save-hook 'quarter-plane-delete-whitespace t)
+    (dolist (sym quarter-plane-saved-symbols)
+      (set sym (pop quarter-plane-saved-values))))))
+
+;;;###autoload
+(define-global-minor-mode global-quarter-plane-mode quarter-plane-mode
+  turn-on-quarter-plane-mode
+  :group 'picture)
+
+(defun quarter-plane-delete-whitespace ()
+  "Call `delete-trailing-whitespace' if the buffer is not read-only."
+  (if (not buffer-read-only)
+      (delete-trailing-whitespace)))
+
+(add-hook 'quarter-plane-mode-off-hook 'quarter-plane-delete-whitespace)
+
+(provide 'quarter-plane)
+
+;;; quarter-plane.el ends here