lisp/tabify.el

   1 ;;; tabify.el --- tab conversion commands for Emacs
   2
   3 ;; Copyright (C) 1985, 1994, 2001-2011 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   (save-excursion
  38     (save-restriction
  39       (narrow-to-region (point-min) end)
  40       (goto-char start)
  41       (while (search-forward "\t" nil t)        ; faster than re-search
  42         (forward-char -1)
  43         (let ((tab-beg (point))
  44               (indent-tabs-mode nil)
  45               column)
  46           (skip-chars-forward "\t")
  47           (setq column (current-column))
  48           (delete-region tab-beg (point))
  49           (indent-to column))))))
  50
  51 (defvar tabify-regexp " [ \t]+"
  52   "Regexp matching whitespace that tabify should consider.
  53 Usually this will be \" [ \\t]+\" to match a space followed by whitespace.
  54 \"^\\t* [ \\t]+\" is also useful, for tabifying only initial whitespace.")
  55
  56 ;;;###autoload
  57 (defun tabify (start end)
  58   "Convert multiple spaces in region to tabs when possible.
  59 A group of spaces is partially replaced by tabs
  60 when this can be done without changing the column they end at.
  61 Called non-interactively, the region is specified by arguments
  62 START and END, rather than by the position of point and mark.
  63 The variable `tab-width' controls the spacing of tab stops."
  64   (interactive "r")
  65   (save-excursion
  66     (save-restriction
  67       ;; Include the beginning of the line in the narrowing
  68       ;; since otherwise it will throw off current-column.
  69       (goto-char start)
  70       (beginning-of-line)
  71       (narrow-to-region (point) end)
  72       (goto-char start)
  73       (let ((indent-tabs-mode t))
  74         (while (re-search-forward tabify-regexp nil t)
  75           ;; The region between (match-beginning 0) and (match-end 0) is just
  76           ;; spacing which we want to adjust to use TABs where possible.
  77           (let ((end-col (current-column))
  78                 (beg-col (save-excursion (goto-char (match-beginning 0))
  79                                          (skip-chars-forward "\t")
  80                                          (current-column))))
  81             (if (= (/ end-col tab-width) (/ beg-col tab-width))
  82                 ;; The spacing (after some leading TABs which we wouldn't
  83                 ;; want to touch anyway) does not straddle a TAB boundary,
  84                 ;; so it neither contains a TAB, nor will we be able to use
  85                 ;; a TAB here anyway: there's nothing to do.
  86                 nil
  87               (delete-region (match-beginning 0) (point))
  88               (indent-to end-col))))))))
  89
  90 (provide 'tabify)
  91
  92 ;;; tabify.el ends here