Emacs lisp function to toggle variable 'tab-width' between 4 & 8

Question

The source tree that I work on has files indented with different tab values, (not to mention spaces) and the best I can do is to set emacs to use the style found in the region of code I am modifying. Instead of doing M-x set-variable tab-width to 4 or 8, a key binding to toggle the tab-width among these two value would help immensely.

Thanks.

Answer 1

Throw this in your .emacs or .emacs.d/init.el file:

(defun toggle-spaces ()
  "Toggle tab-width between 4 and 8"
  (interactive)
  (if (eq tab-width 4)
      (setq tab-width 8)
    (setq tab-width 4)))

;; This will set Ctrl-g to toggle but you can set it to anything
;; you want.
(global-set-key "\C-g" 'toggle-spaces)

Answer 2

;; Obviously substitute your preferred key for <f8>
(global-set-key (kbd "<f8>") 'tf-toggle-tab-width-setting) ; ' "fix" highlighting

(defun tf-toggle-tab-width-setting ()
    "Toggle setting tab widths between 4 and 8"
    (interactive)
    (setq tab-width (if (= tab-width 8) 4 8))
    (redraw-display))

Edited to add redraw-display as per comment suggested

Answer 3

Not quite answering the question (the answers given are good enough), but you might want to consider setting a per-file local variable. For example, assuming that "//" means comment in your language, you would put the following in the first line of the file:

// -*- tab-width: 4 -*-

And emacs will set the variable for you whenever you visit the file. See http://www.gnu.org/software/emacs/manual/html_node/emacs/Specifying-File-Variables.html for more information on file-based variables.

Of course this might not be a choice if the file is shared among a group - unless you can convince your colleges that this first line comment is completely harmless and extremely useful!

Answer 4

Thanks for all the answers. I added a redraw-display call so that the change is reflected immediately. (Tried posting this as a comment, but can't.)

(global-set-key (kbd "<f8>") 'tf-toggle-tab-width-setting)
(defun tf-toggle-tab-width-setting ()    "toggle setting tab widths between 4 and 8"
    (interactive)
    (setq tab-width (if (= tab-width 8) 4 8))
    (message "set tab-width to %d." tab-width)
    (redraw-display)
)

And along the same lines. :(

(global-set-key (kbd "<f7>") 'tf-toggle-indent-mode-setting)
(defun tf-toggle-indent-mode-setting ()
    "toggle indenting modes"
    (interactive)
    (setq indent-tabs-mode (if (eq indent-tabs-mode t) nil t))
    (message "Indenting using %s." (if (eq indent-tabs-mode t) "tabs" "spaces"))
)