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[emacs.git] / lisp / tabify.el
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1 ;;; tabify.el --- tab conversion commands for Emacs
3 ;; Copyright (C) 1985, 1994, 2001-2014 Free Software Foundation, Inc.
5 ;; Maintainer: emacs-devel@gnu.org
6 ;; Package: emacs
8 ;; This file is part of GNU Emacs.
10 ;; GNU Emacs is free software: you can redistribute it and/or modify
11 ;; it under the terms of the GNU General Public License as published by
12 ;; the Free Software Foundation, either version 3 of the License, or
13 ;; (at your option) any later version.
15 ;; GNU Emacs is distributed in the hope that it will be useful,
16 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
17 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
18 ;; GNU General Public License for more details.
20 ;; You should have received a copy of the GNU General Public License
21 ;; along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>.
23 ;;; Commentary:
25 ;; Commands to optimize spaces to tabs or expand tabs to spaces in a region
26 ;; (`tabify' and `untabify'). The variable tab-width does the obvious.
28 ;;; Code:
30 ;;;###autoload
31 (defun untabify (start end &optional _arg)
32 "Convert all tabs in region to multiple spaces, preserving columns.
33 If called interactively with prefix ARG, convert for the entire
34 buffer.
36 Called non-interactively, the region is specified by arguments
37 START and END, rather than by the position of point and mark.
38 The variable `tab-width' controls the spacing of tab stops."
39 (interactive (if current-prefix-arg
40 (list (point-min) (point-max) current-prefix-arg)
41 (list (region-beginning) (region-end) nil)))
42 (let ((c (current-column)))
43 (save-excursion
44 (save-restriction
45 (narrow-to-region (point-min) end)
46 (goto-char start)
47 (while (search-forward "\t" nil t) ; faster than re-search
48 (forward-char -1)
49 (let ((tab-beg (point))
50 (indent-tabs-mode nil)
51 column)
52 (skip-chars-forward "\t")
53 (setq column (current-column))
54 (delete-region tab-beg (point))
55 (indent-to column)))))
56 (move-to-column c)))
58 (defvar tabify-regexp " [ \t]+"
59 "Regexp matching whitespace that tabify should consider.
60 Usually this will be \" [ \\t]+\" to match a space followed by whitespace.
61 \"^\\t* [ \\t]+\" is also useful, for tabifying only initial whitespace.")
63 ;;;###autoload
64 (defun tabify (start end &optional _arg)
65 "Convert multiple spaces in region to tabs when possible.
66 A group of spaces is partially replaced by tabs
67 when this can be done without changing the column they end at.
68 If called interactively with prefix ARG, convert for the entire
69 buffer.
71 Called non-interactively, the region is specified by arguments
72 START and END, rather than by the position of point and mark.
73 The variable `tab-width' controls the spacing of tab stops."
74 (interactive (if current-prefix-arg
75 (list (point-min) (point-max) current-prefix-arg)
76 (list (region-beginning) (region-end) nil)))
77 (save-excursion
78 (save-restriction
79 ;; Include the beginning of the line in the narrowing
80 ;; since otherwise it will throw off current-column.
81 (goto-char start)
82 (beginning-of-line)
83 (narrow-to-region (point) end)
84 (goto-char start)
85 (let ((indent-tabs-mode t))
86 (while (re-search-forward tabify-regexp nil t)
87 ;; The region between (match-beginning 0) and (match-end 0) is just
88 ;; spacing which we want to adjust to use TABs where possible.
89 (let ((end-col (current-column))
90 (beg-col (save-excursion (goto-char (match-beginning 0))
91 (skip-chars-forward "\t")
92 (current-column))))
93 (if (= (/ end-col tab-width) (/ beg-col tab-width))
94 ;; The spacing (after some leading TABs which we wouldn't
95 ;; want to touch anyway) does not straddle a TAB boundary,
96 ;; so it neither contains a TAB, nor will we be able to use
97 ;; a TAB here anyway: there's nothing to do.
98 nil
99 (delete-region (match-beginning 0) (point))
100 (indent-to end-col))))))))
102 (provide 'tabify)
104 ;;; tabify.el ends here