lisp/tabify.el

   1 ;;; tabify.el --- tab conversion commands for Emacs
   2
   3 ;; Copyright (C) 1985, 1994, 2001-2012 Free Software Foundation, Inc.
   4
   5 ;; Maintainer: FSF
   6 ;; Package: emacs
   7
   8 ;; This file is part of GNU Emacs.
   9
  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.
  14
  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.
  19
  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/>.
  22
  23 ;;; Commentary:
  24
  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.
  27
  28 ;;; Code:
  29
  30 ;;;###autoload
  31 (defun untabify (start end)
  32   "Convert all tabs in region to multiple spaces, preserving columns.
  33 Called non-interactively, the region is specified by arguments
  34 START and END, rather than by the position of point and mark.
  35 The variable `tab-width' controls the spacing of tab stops."
  36   (interactive "r")
  37   (let ((c (current-column)))
  38     (save-excursion
  39       (save-restriction
  40         (narrow-to-region (point-min) end)
  41         (goto-char start)
  42         (while (search-forward "\t" nil t)      ; faster than re-search
  43           (forward-char -1)
  44           (let ((tab-beg (point))
  45                 (indent-tabs-mode nil)
  46                 column)
  47             (skip-chars-forward "\t")
  48             (setq column (current-column))
  49             (delete-region tab-beg (point))
  50             (indent-to column)))))
  51     (move-to-column c)))
  52
  53 (defvar tabify-regexp " [ \t]+"
  54   "Regexp matching whitespace that tabify should consider.
  55 Usually this will be \" [ \\t]+\" to match a space followed by whitespace.
  56 \"^\\t* [ \\t]+\" is also useful, for tabifying only initial whitespace.")
  57
  58 ;;;###autoload
  59 (defun tabify (start end)
  60   "Convert multiple spaces in region to tabs when possible.
  61 A group of spaces is partially replaced by tabs
  62 when this can be done without changing the column they end at.
  63 Called non-interactively, the region is specified by arguments
  64 START and END, rather than by the position of point and mark.
  65 The variable `tab-width' controls the spacing of tab stops."
  66   (interactive "r")
  67   (save-excursion
  68     (save-restriction
  69       ;; Include the beginning of the line in the narrowing
  70       ;; since otherwise it will throw off current-column.
  71       (goto-char start)
  72       (beginning-of-line)
  73       (narrow-to-region (point) end)
  74       (goto-char start)
  75       (let ((indent-tabs-mode t))
  76         (while (re-search-forward tabify-regexp nil t)
  77           ;; The region between (match-beginning 0) and (match-end 0) is just
  78           ;; spacing which we want to adjust to use TABs where possible.
  79           (let ((end-col (current-column))
  80                 (beg-col (save-excursion (goto-char (match-beginning 0))
  81                                          (skip-chars-forward "\t")
  82                                          (current-column))))
  83             (if (= (/ end-col tab-width) (/ beg-col tab-width))
  84                 ;; The spacing (after some leading TABs which we wouldn't
  85                 ;; want to touch anyway) does not straddle a TAB boundary,
  86                 ;; so it neither contains a TAB, nor will we be able to use
  87                 ;; a TAB here anyway: there's nothing to do.
  88                 nil
  89               (delete-region (match-beginning 0) (point))
  90               (indent-to end-col))))))))
  91
  92 (provide 'tabify)
  93
  94 ;;; tabify.el ends here