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;;; tabify.el --- tab conversion commands for Emacs
;; Copyright (C) 1985, 1994, 2001-2013 Free Software Foundation, Inc.
;; Maintainer: FSF
;; Package: emacs
;; 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 3 of the License, 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. If not, see <http://www.gnu.org/licenses/>.
;;; Commentary:
;; Commands to optimize spaces to tabs or expand tabs to spaces in a region
;; (`tabify' and `untabify'). The variable tab-width does the obvious.
;;; Code:
;;;###autoload
(defun untabify (start end)
"Convert all tabs in region to multiple spaces, preserving columns.
Called non-interactively, the region is specified by arguments
START and END, rather than by the position of point and mark.
The variable `tab-width' controls the spacing of tab stops."
(interactive "r")
(let ((c (current-column)))
(save-excursion
(save-restriction
(narrow-to-region (point-min) end)
(goto-char start)
(while (search-forward "\t" nil t) ; faster than re-search
(forward-char -1)
(let ((tab-beg (point))
(indent-tabs-mode nil)
column)
(skip-chars-forward "\t")
(setq column (current-column))
(delete-region tab-beg (point))
(indent-to column)))))
(move-to-column c)))
(defvar tabify-regexp " [ \t]+"
"Regexp matching whitespace that tabify should consider.
Usually this will be \" [ \\t]+\" to match a space followed by whitespace.
\"^\\t* [ \\t]+\" is also useful, for tabifying only initial whitespace.")
;;;###autoload
(defun tabify (start end)
"Convert multiple spaces in region to tabs when possible.
A group of spaces is partially replaced by tabs
when this can be done without changing the column they end at.
Called non-interactively, the region is specified by arguments
START and END, rather than by the position of point and mark.
The variable `tab-width' controls the spacing of tab stops."
(interactive "r")
(save-excursion
(save-restriction
;; Include the beginning of the line in the narrowing
;; since otherwise it will throw off current-column.
(goto-char start)
(beginning-of-line)
(narrow-to-region (point) end)
(goto-char start)
(let ((indent-tabs-mode t))
(while (re-search-forward tabify-regexp nil t)
;; The region between (match-beginning 0) and (match-end 0) is just
;; spacing which we want to adjust to use TABs where possible.
(let ((end-col (current-column))
(beg-col (save-excursion (goto-char (match-beginning 0))
(skip-chars-forward "\t")
(current-column))))
(if (= (/ end-col tab-width) (/ beg-col tab-width))
;; The spacing (after some leading TABs which we wouldn't
;; want to touch anyway) does not straddle a TAB boundary,
;; so it neither contains a TAB, nor will we be able to use
;; a TAB here anyway: there's nothing to do.
nil
(delete-region (match-beginning 0) (point))
(indent-to end-col))))))))
(provide 'tabify)
;;; tabify.el ends here
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