emacs/lisp/textmodes/outline.el

;;; outline.el --- outline mode commands for Emacs

;; Copyright (C) 1986, 1993, 1994, 1995, 1997 Free Software Foundation, Inc.

;; Maintainer: FSF
;; Keywords: outlines

;; 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:

;; This package is a major mode for editing outline-format documents.
;; An outline can be `abstracted' to show headers at any given level,
;; with all stuff below hidden.  See the Emacs manual for details.

;;; Code:

(defgroup outlines nil
  "Support for hierarchical outlining"
  :prefix "outline-"
  :group 'editing)

(defcustom outline-regexp nil
  "*Regular expression to match the beginning of a heading.
Any line whose beginning matches this regexp is considered to start a heading.
The recommended way to set this is with a Local Variables: list
in the file it applies to.  See also outline-heading-end-regexp."
  :type '(choice regexp (const nil))
  :group 'outlines)

;; Can't initialize this in the defvar above -- some major modes have
;; already assigned a local value to it.
(or (default-value 'outline-regexp)
    (setq-default outline-regexp "[*\^L]+"))
  
(defcustom outline-heading-end-regexp "\n"
  "*Regular expression to match the end of a heading line.
You can assume that point is at the beginning of a heading when this
regexp is searched for.  The heading ends at the end of the match.
The recommended way to set this is with a `Local Variables:' list
in the file it applies to."
  :type 'regexp
  :group 'outlines)

(defvar outline-mode-prefix-map nil)

(if outline-mode-prefix-map
    nil
  (setq outline-mode-prefix-map (make-sparse-keymap))
  (define-key outline-mode-prefix-map "@" 'outline-mark-subtree)
  (define-key outline-mode-prefix-map "\C-n" 'outline-next-visible-heading)
  (define-key outline-mode-prefix-map "\C-p" 'outline-previous-visible-heading)
  (define-key outline-mode-prefix-map "\C-i" 'show-children)
  (define-key outline-mode-prefix-map "\C-s" 'show-subtree)
  (define-key outline-mode-prefix-map "\C-d" 'hide-subtree)
  (define-key outline-mode-prefix-map "\C-u" 'outline-up-heading)
  (define-key outline-mode-prefix-map "\C-f" 'outline-forward-same-level)
  (define-key outline-mode-prefix-map "\C-b" 'outline-backward-same-level)
  (define-key outline-mode-prefix-map "\C-t" 'hide-body)
  (define-key outline-mode-prefix-map "\C-a" 'show-all)
  (define-key outline-mode-prefix-map "\C-c" 'hide-entry)
  (define-key outline-mode-prefix-map "\C-e" 'show-entry)
  (define-key outline-mode-prefix-map "\C-l" 'hide-leaves)
  (define-key outline-mode-prefix-map "\C-k" 'show-branches)
  (define-key outline-mode-prefix-map "\C-q" 'hide-sublevels)
  (define-key outline-mode-prefix-map "\C-o" 'hide-other))

(defvar outline-mode-menu-bar-map nil)
(if outline-mode-menu-bar-map
    nil
  (setq outline-mode-menu-bar-map (make-sparse-keymap))

  (define-key outline-mode-menu-bar-map [hide]
    (cons "Hide" (make-sparse-keymap "Hide")))

  (define-key outline-mode-menu-bar-map [hide hide-other]
    '("Hide Other" . hide-other))
  (define-key outline-mode-menu-bar-map [hide hide-sublevels]
    '("Hide Sublevels" . hide-sublevels))
  (define-key outline-mode-menu-bar-map [hide hide-subtree]
    '("Hide Subtree" . hide-subtree))
  (define-key outline-mode-menu-bar-map [hide hide-entry]
    '("Hide Entry" . hide-entry))
  (define-key outline-mode-menu-bar-map [hide hide-body]
    '("Hide Body" . hide-body))
  (define-key outline-mode-menu-bar-map [hide hide-leaves]
    '("Hide Leaves" . hide-leaves))

  (define-key outline-mode-menu-bar-map [show]
    (cons "Show" (make-sparse-keymap "Show")))

  (define-key outline-mode-menu-bar-map [show show-subtree]
    '("Show Subtree" . show-subtree))
  (define-key outline-mode-menu-bar-map [show show-children]
    '("Show Children" . show-children))
  (define-key outline-mode-menu-bar-map [show show-branches]
    '("Show Branches" . show-branches))
  (define-key outline-mode-menu-bar-map [show show-entry]
    '("Show Entry" . show-entry))
  (define-key outline-mode-menu-bar-map [show show-all]
    '("Show All" . show-all))

  (define-key outline-mode-menu-bar-map [headings]
    (cons "Headings" (make-sparse-keymap "Headings")))

  (define-key outline-mode-menu-bar-map [headings outline-backward-same-level]
    '("Previous Same Level" . outline-backward-same-level))
  (define-key outline-mode-menu-bar-map [headings outline-forward-same-level]
    '("Next Same Level" . outline-forward-same-level))
  (define-key outline-mode-menu-bar-map [headings outline-previous-visible-heading]
    '("Previous" . outline-previous-visible-heading))
  (define-key outline-mode-menu-bar-map [headings outline-next-visible-heading]
    '("Next" . outline-next-visible-heading))
  (define-key outline-mode-menu-bar-map [headings outline-up-heading]
    '("Up" . outline-up-heading)))

(defvar outline-mode-map nil "")

(if outline-mode-map
    nil
  (setq outline-mode-map (nconc (make-sparse-keymap) text-mode-map))
  (define-key outline-mode-map "\C-c" outline-mode-prefix-map)
  (define-key outline-mode-map [menu-bar] outline-mode-menu-bar-map))

(defcustom outline-minor-mode nil
  "Non-nil if using Outline mode as a minor mode of some other mode."
  :type 'boolean
  :group 'outlines)
(make-variable-buffer-local 'outline-minor-mode)
(or (assq 'outline-minor-mode minor-mode-alist)
    (setq minor-mode-alist (append minor-mode-alist
				   (list '(outline-minor-mode " Outl")))))

(defvar outline-font-lock-keywords
  '(;;
    ;; Highlight headings according to the level.
    (eval . (list (concat "^" outline-regexp ".+")
		  0 '(or (cdr (assq (outline-font-lock-level)
				    '((1 . font-lock-function-name-face)
				      (2 . font-lock-variable-name-face)
				      (3 . font-lock-keyword-face)
				      (4 . font-lock-builtin-face)
				      (5 . font-lock-comment-face)
				      (6 . font-lock-reference-face)
				      (7 . font-lock-type-face)
				      (8 . font-lock-string-face))))
			 font-lock-warning-face)
		  nil t)))
  "Additional expressions to highlight in Outline mode.")

(defvar outline-view-change-hook nil
  "Normal hook to be run after outline visibility changes.")

;;;###autoload
(defun outline-mode ()
  "Set major mode for editing outlines with selective display.
Headings are lines which start with asterisks: one for major headings,
two for subheadings, etc.  Lines not starting with asterisks are body lines. 

Body text or subheadings under a heading can be made temporarily
invisible, or visible again.  Invisible lines are attached to the end 
of the heading, so they move with it, if the line is killed and yanked
back.  A heading with text hidden under it is marked with an ellipsis (...).

Commands:\\<outline-mode-map>
\\[outline-next-visible-heading]   outline-next-visible-heading      move by visible headings
\\[outline-previous-visible-heading]   outline-previous-visible-heading
\\[outline-forward-same-level]   outline-forward-same-level        similar but skip subheadings
\\[outline-backward-same-level]   outline-backward-same-level
\\[outline-up-heading]   outline-up-heading		    move from subheading to heading

\\[hide-body]	make all text invisible (not headings).
\\[show-all]	make everything in buffer visible.

The remaining commands are used when point is on a heading line.
They apply to some of the body or subheadings of that heading.
\\[hide-subtree]   hide-subtree	make body and subheadings invisible.
\\[show-subtree]   show-subtree	make body and subheadings visible.
\\[show-children]   show-children	make direct subheadings visible.
		 No effect on body, or subheadings 2 or more levels down.
		 With arg N, affects subheadings N levels down.
\\[hide-entry]	   make immediately following body invisible.
\\[show-entry]	   make it visible.
\\[hide-leaves]	   make body under heading and under its subheadings invisible.
		     The subheadings remain visible.
\\[show-branches]  make all subheadings at all levels visible.

The variable `outline-regexp' can be changed to control what is a heading.
A line is a heading if `outline-regexp' matches something at the
beginning of the line.  The longer the match, the deeper the level.

Turning on outline mode calls the value of `text-mode-hook' and then of
`outline-mode-hook', if they are non-nil."
  (interactive)
  (kill-all-local-variables)
  (use-local-map outline-mode-map)
  (setq mode-name "Outline")
  (setq major-mode 'outline-mode)
  (define-abbrev-table 'text-mode-abbrev-table ())
  (setq local-abbrev-table text-mode-abbrev-table)
  (set-syntax-table text-mode-syntax-table)
  (make-local-variable 'line-move-ignore-invisible)
  (setq line-move-ignore-invisible t)
  ;; Cause use of ellipses for invisible text.
  (add-to-invisibility-spec '(outline . t))
  (make-local-variable 'paragraph-start)
  (setq paragraph-start (concat paragraph-start "\\|\\("
				outline-regexp "\\)"))
  ;; Inhibit auto-filling of header lines.
  (make-local-variable 'auto-fill-inhibit-regexp)
  (setq auto-fill-inhibit-regexp outline-regexp)
  (make-local-variable 'paragraph-separate)
  (setq paragraph-separate (concat paragraph-separate "\\|\\("
				   outline-regexp "\\)"))
  (make-local-variable 'font-lock-defaults)
  (setq font-lock-defaults '(outline-font-lock-keywords t))
  (make-local-variable 'change-major-mode-hook)
  (add-hook 'change-major-mode-hook 'show-all)
  (run-hooks 'text-mode-hook 'outline-mode-hook))

(defcustom outline-minor-mode-prefix "\C-c@"
  "*Prefix key to use for Outline commands in Outline minor mode.
The value of this variable is checked as part of loading Outline mode.
After that, changing the prefix key requires manipulating keymaps."
  :type 'string
  :group 'outlines)

(defvar outline-minor-mode-map nil)
(if outline-minor-mode-map
    nil
  (setq outline-minor-mode-map (make-sparse-keymap))
  (define-key outline-minor-mode-map [menu-bar]
    outline-mode-menu-bar-map)
  (define-key outline-minor-mode-map outline-minor-mode-prefix
    outline-mode-prefix-map))

(or (assq 'outline-minor-mode minor-mode-map-alist)
    (setq minor-mode-map-alist
	  (cons (cons 'outline-minor-mode outline-minor-mode-map)
		minor-mode-map-alist)))

;;;###autoload
(defun outline-minor-mode (&optional arg)
  "Toggle Outline minor mode.
With arg, turn Outline minor mode on if arg is positive, off otherwise.
See the command `outline-mode' for more information on this mode."
  (interactive "P")
  (setq outline-minor-mode
	(if (null arg) (not outline-minor-mode)
	  (> (prefix-numeric-value arg) 0)))
  (if outline-minor-mode
      (progn
	(make-local-hook 'change-major-mode-hook)
	;; Turn off this mode if we change major modes.
	(add-hook 'change-major-mode-hook
		  '(lambda () (outline-minor-mode -1))
		  nil t)
	(make-local-variable 'line-move-ignore-invisible)
	(setq line-move-ignore-invisible t)
	;; Cause use of ellipses for invisible text.
	(add-to-invisibility-spec '(outline . t))
	(run-hooks 'outline-minor-mode-hook))
    (setq line-move-ignore-invisible nil)
    ;; Cause use of ellipses for invisible text.
    (remove-from-invisibility-spec '(outline . t)))
  ;; When turning off outline mode, get rid of any outline hiding.
  (or outline-minor-mode
      (show-all))
  (force-mode-line-update))

(defcustom outline-level 'outline-level
  "*Function of no args to compute a header's nesting level in an outline.
It can assume point is at the beginning of a header line."
  :type 'function
  :group 'outlines)

;; This used to count columns rather than characters, but that made ^L
;; appear to be at level 2 instead of 1.  Columns would be better for
;; tab handling, but the default regexp doesn't use tabs, and anyone
;; who changes the regexp can also redefine the outline-level variable
;; as appropriate.
(defun outline-level ()
  "Return the depth to which a statement is nested in the outline.
Point must be at the beginning of a header line.  This is actually
the number of characters that `outline-regexp' matches."
  (save-excursion
    (looking-at outline-regexp)
    (- (match-end 0) (match-beginning 0))))

(defun outline-next-preface ()
  "Skip forward to just before the next heading line.
If there's no following heading line, stop before the newline
at the end of the buffer."
  (if (re-search-forward (concat "\n\\(" outline-regexp "\\)")
			 nil 'move)
      (goto-char (match-beginning 0)))
  (if (and (bolp) (not (bobp)))
      (forward-char -1)))

(defun outline-next-heading ()
  "Move to the next (possibly invisible) heading line."
  (interactive)
  (if (re-search-forward (concat "\n\\(" outline-regexp "\\)")
			 nil 'move)
      (goto-char (1+ (match-beginning 0)))))

(defsubst outline-visible ()
  "Non-nil if the character after point is visible."
  (not (get-char-property (point) 'invisible)))

(defun outline-back-to-heading (&optional invisible-ok)
  "Move to previous heading line, or beg of this line if it's a heading.
Only visible heading lines are considered, unless INVISIBLE-OK is non-nil."
  (beginning-of-line)
  (or (outline-on-heading-p t)
      (let (found)
	(save-excursion
	  (while (not found)
	    (or (re-search-backward (concat "^\\(" outline-regexp "\\)")
				    nil t)
		(error "before first heading"))
	    (setq found (and (or invisible-ok (outline-visible)) (point)))))
	(goto-char found)
	found)))

(defun outline-on-heading-p (&optional invisible-ok)
  "Return t if point is on a (visible) heading line.
If INVISIBLE-OK is non-nil, an invisible heading line is ok too."
  (save-excursion
    (beginning-of-line)
    (and (bolp) (or invisible-ok (outline-visible))
	 (looking-at outline-regexp))))

(defun outline-end-of-heading ()
  (if (re-search-forward outline-heading-end-regexp nil 'move)
      (forward-char -1)))

(defun outline-next-visible-heading (arg)
  "Move to the next visible heading line.
With argument, repeats or can move backward if negative.
A heading line is one that starts with a `*' (or that
`outline-regexp' matches)."
  (interactive "p")
  (if (< arg 0)
      (beginning-of-line)
    (end-of-line))
  (while (and (not (bobp)) (< arg 0))
    (while (and (not (bobp))
		(re-search-backward (concat "^\\(" outline-regexp "\\)")
				    nil 'move)
		(not (outline-visible))))
    (setq arg (1+ arg)))
  (while (and (not (eobp)) (> arg 0))
    (while (and (not (eobp))
		(re-search-forward (concat "^\\(" outline-regexp "\\)")
				   nil 'move)
		(not (outline-visible))))
    (setq arg (1- arg)))
  (beginning-of-line))

(defun outline-previous-visible-heading (arg)
  "Move to the previous heading line.
With argument, repeats or can move forward if negative.
A heading line is one that starts with a `*' (or that
`outline-regexp' matches)."
  (interactive "p")
  (outline-next-visible-heading (- arg)))

(defun outline-mark-subtree ()
  "Mark the current subtree in an outlined document.
This puts point at the start of the current subtree, and mark at the end."
  (interactive)
  (let ((beg))
    (if (outline-on-heading-p)
	;; we are already looking at a heading
	(beginning-of-line)
      ;; else go back to previous heading
      (outline-previous-visible-heading 1))
    (setq beg (point))
    (outline-end-of-subtree)
    (push-mark (point))
    (goto-char beg)))

(defun outline-flag-region (from to flag)
  "Hides or shows lines from FROM to TO, according to FLAG.
If FLAG is nil then text is shown, while if FLAG is t the text is hidden."
  (let ((inhibit-read-only t))
    (save-excursion
      (goto-char from)
      (end-of-line)
      (outline-discard-overlays (point) to 'outline)
      (if flag
	  (let ((o (make-overlay (point) to)))
	    (overlay-put o 'invisible 'outline)
	    (overlay-put o 'outline t)))))
  (run-hooks 'outline-view-change-hook))

;; Exclude from the region BEG ... END all overlays
;; with a non-nil PROP property.
;; Exclude them by shrinking them to exclude BEG ... END,
;; or even by splitting them if necessary.
;; Overlays without a non-nil PROP property are not touched.
(defun outline-discard-overlays (beg end prop)
  (if (< end beg)
      (setq beg (prog1 end (setq end beg))))
  (save-excursion
    (let ((overlays (overlays-in beg end))
	  o
	  o1)
      (while overlays
	(setq o (car overlays))
	(if (overlay-get o prop)
	    ;; Either push this overlay outside beg...end
	    ;; or split it to exclude beg...end
	    ;; or delete it entirely (if it is contained in beg...end).
	    (if (< (overlay-start o) beg)
		(if (> (overlay-end o) end)
		    (progn 
		      (setq o1 (outline-copy-overlay o))
		      (move-overlay o1 (overlay-start o1) beg)
		      (move-overlay o end (overlay-end o)))
		  (move-overlay o (overlay-start o) beg))
	      (if (> (overlay-end o) end)
		  (move-overlay o end (overlay-end o))
		(delete-overlay o))))
	(setq overlays (cdr overlays))))))

;; Make a copy of overlay O, with the same beginning, end and properties.
(defun outline-copy-overlay (o)
  (let ((o1 (make-overlay (overlay-start o) (overlay-end o)
			  (overlay-buffer o)))
	(props (overlay-properties o)))
    (while props
      (overlay-put o1 (car props) (nth 1 props))
      (setq props (cdr (cdr props))))
    o1))

(defun hide-entry ()
  "Hide the body directly following this heading."
  (interactive)
  (outline-back-to-heading)
  (outline-end-of-heading)
  (save-excursion
   (outline-flag-region (point) (progn (outline-next-preface) (point)) t)))

(defun show-entry ()
  "Show the body directly following this heading.
Show the heading too, if it is currently invisible."
  (interactive)
  (save-excursion
    (outline-back-to-heading t)
    (outline-flag-region (1- (point))
			 (progn (outline-next-preface) (point)) nil)))

(defun hide-body ()
  "Hide all of buffer except headings."
  (interactive)
  (hide-region-body (point-min) (point-max)))

(defun hide-region-body (start end)
  "Hide all body lines in the region, but not headings."
  (save-excursion
    (save-restriction
      (narrow-to-region start end)
      (goto-char (point-min))
      (if (outline-on-heading-p)
	  (outline-end-of-heading))
      (while (not (eobp))
	(outline-flag-region (point)
			     (progn (outline-next-preface) (point)) t)
	(if (not (eobp))
	    (progn
	      (forward-char
	       (if (looking-at "\n\n")
		   2 1))
	      (outline-end-of-heading)))))))

(defun show-all ()
  "Show all of the text in the buffer."
  (interactive)
  (outline-flag-region (point-min) (point-max) nil))

(defun hide-subtree ()
  "Hide everything after this heading at deeper levels."
  (interactive)
  (outline-flag-subtree t))

(defun hide-leaves ()
  "Hide all body after this heading at deeper levels."
  (interactive)
  (outline-back-to-heading)
  (outline-end-of-heading)
  (hide-region-body (point) (progn (outline-end-of-subtree) (point))))

(defun show-subtree ()
  "Show everything after this heading at deeper levels."
  (interactive)
  (outline-flag-subtree nil))

(defun hide-sublevels (levels)
  "Hide everything but the top LEVELS levels of headers, in whole buffer."
  (interactive "p")
  (if (< levels 1)
      (error "Must keep at least one level of headers"))
  (setq levels (1- levels))
  (save-excursion
    (goto-char (point-min))
    ;; Keep advancing to the next top-level heading.
    (while (or (and (bobp) (outline-on-heading-p))
	       (outline-next-heading))
      (let ((end (save-excursion (outline-end-of-subtree) (point))))
	;; Hide everything under that.
	(outline-flag-region (point) end t)
	;; Show the first LEVELS levels under that.
	(if (> levels 0)
	    (show-children levels))
	;; Move to the next, since we already found it.
	(goto-char end)))))

(defun hide-other ()
  "Hide everything except current body and parent and top-level headings."
  (interactive)
  (hide-sublevels 1)
  (save-excursion
    (outline-back-to-heading t)
    (show-entry)
    (while (condition-case nil (progn (outline-up-heading 1) t) (error nil))
      (outline-flag-region (1- (point))
			   (save-excursion (forward-line 1) (point))
			   nil))))

(defun outline-flag-subtree (flag)
  (save-excursion
    (outline-back-to-heading)
    (outline-end-of-heading)
    (outline-flag-region (point)
			  (progn (outline-end-of-subtree) (point))
			  flag)))

(defun outline-end-of-subtree ()
  (outline-back-to-heading)
  (let ((opoint (point))
	(first t)
	(level (funcall outline-level)))
    (while (and (not (eobp))
		(or first (> (funcall outline-level) level)))
      (setq first nil)
      (outline-next-heading))
    (if (bolp)
	(progn
	  ;; Go to end of line before heading
	  (forward-char -1)
	  (if (bolp)
	      ;; leave blank line before heading
	      (forward-char -1))))))

(defun show-branches ()
  "Show all subheadings of this heading, but not their bodies."
  (interactive)
  (show-children 1000))

(defun show-children (&optional level)
  "Show all direct subheadings of this heading.
Prefix arg LEVEL is how many levels below the current level should be shown.
Default is enough to cause the following heading to appear."
  (interactive "P")
  (setq level
	(if level (prefix-numeric-value level)
	  (save-excursion
	    (outline-back-to-heading)
	    (let ((start-level (funcall outline-level)))
	      (outline-next-heading)
	      (if (eobp)
		  1
		(max 1 (- (funcall outline-level) start-level)))))))
  (save-excursion
    (save-restriction
      (outline-back-to-heading)
      (setq level (+ level (funcall outline-level)))
      (narrow-to-region (point)
			(progn (outline-end-of-subtree)
			       (if (eobp) (point-max) (1+ (point)))))
      (goto-char (point-min))
      (while (and (not (eobp))
		  (progn
		    (outline-next-heading)
		    (not (eobp))))
	(if (<= (funcall outline-level) level)
	    (save-excursion
	      (outline-flag-region (save-excursion
				     (forward-char -1)
				     (if (bolp)
					 (forward-char -1))
				     (point))
				   (progn (outline-end-of-heading) (point))
				   nil)))))))

(defun outline-up-heading (arg)
  "Move to the heading line of which the present line is a subheading.
With argument, move up ARG levels."
  (interactive "p")
  (outline-back-to-heading)
  (if (eq (funcall outline-level) 1)
      (error "Already at top level of the outline"))
  (while (and (> (funcall outline-level) 1)
	      (> arg 0)
	      (not (bobp)))
    (let ((present-level (funcall outline-level)))
      (while (and (not (< (funcall outline-level) present-level))
		  (not (bobp)))
	(outline-previous-visible-heading 1))
      (setq arg (- arg 1)))))

(defun outline-forward-same-level (arg)
  "Move forward to the ARG'th subheading at same level as this one.
Stop at the first and last subheadings of a superior heading."
  (interactive "p")
  (outline-back-to-heading)
  (while (> arg 0)
    (let ((point-to-move-to (save-excursion
			      (outline-get-next-sibling))))  
      (if point-to-move-to
	  (progn
	    (goto-char point-to-move-to)
	    (setq arg (1- arg)))
	(progn
	  (setq arg 0)
	  (error "No following same-level heading"))))))

(defun outline-get-next-sibling ()
  "Move to next heading of the same level, and return point or nil if none."
  (let ((level (funcall outline-level)))
    (outline-next-visible-heading 1)
    (while (and (> (funcall outline-level) level)
		(not (eobp)))
      (outline-next-visible-heading 1))
    (if (< (funcall outline-level) level)
	nil
      (point))))
	
(defun outline-backward-same-level (arg)
  "Move backward to the ARG'th subheading at same level as this one.
Stop at the first and last subheadings of a superior heading."
  (interactive "p")
  (outline-back-to-heading)
  (while (> arg 0)
    (let ((point-to-move-to (save-excursion
			      (outline-get-last-sibling))))
      (if point-to-move-to
	  (progn
	    (goto-char point-to-move-to)
	    (setq arg (1- arg)))
	(progn
	  (setq arg 0)
	  (error "No previous same-level heading"))))))

(defun outline-get-last-sibling ()
  "Move to next heading of the same level, and return point or nil if none."
  (let ((level (funcall outline-level)))
    (outline-previous-visible-heading 1)
    (while (and (> (funcall outline-level) level)
		(not (bobp)))
      (outline-previous-visible-heading 1))
    (if (< (funcall outline-level) level)
	nil
        (point))))

(provide 'outline)
(provide 'noutline)

;;; outline.el ends here