Question

EMACS 24.1.
I need to Rebind Ctrl-space to a custom function that:

• go to end of line
• delete trailing spaces if any
• set the Mark (as normal Ctrl-space)

This is my code not working:

(define-key global-map [?\C- ] 'my-set-mark-command)
(defun my-set-mark-command()
   (interactive)
   (end-of-line)
   (delete-char (* -1 (skip-chars-backward "\t\s")));;delete trailing spaces
   (set-mark-command nil))

When no trailing spaces it works normally: start to select and highlight the region.
When trailing spaces: it deletes trailing spaces, stop at end of line, set Mark but don’t highlight the region.

If I remove the last command (set-mark-command) and I run it manually M-xset-mark-command it works.
Please can somebody help me to make this function works properly??

Answer 1

Modification commands cause the variable deactivate-mark to be reset, causing the mark to be lost. In the documentation for save-excursion it says how to disable that behavior, by binding the deactivate-mark variable with let. You can then change the code to:

(defun my-set-mark-command ()
   (interactive)
   (end-of-line)
   (let (deactivate-mark)
     (delete-char (* -1 (skip-chars-backward "\t\s"))))  ;;delete trailing spaces
   (set-mark-command nil))

or even include the whole let inside a save-excursion.

See manual:

http://www.gnu.org/software/emacs/manual/html_node/elisp/The-Mark.html#index-deactivate_002dmark-2801