There is an unfill-paragraph mentioned here that does the opposite of fill-paragraph. I would like to bind the key like the follows. M-q once to fill-paragraph. If the cursor does not move, push M-q again to unfill-paragraph. What is an elegant way to implement this in Emacs?


The answer provided by @icarus does not let you keep toggling back and forth. If you want that then you also need to set this-command, so that it alternates.

(defun my-fill-paragraph (&optional arg)
  "Fill or unfill paragraph.  If repeated, alternate.
A prefix arg for filling means justify (as for `fill-paragraph')."
  (interactive "P")
  (let ((fillp  (not (eq last-command 'fill-paragraph))))
    (apply (setq this-command  (if fillp 'fill-paragraph 'unfill-paragraph))
           (and fillp  arg  '(full t)))))
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  • 1
    Using "icarus's answer" rather than "the answer of @icarus" stops stack exchange from notifying me. In general I dislike updating this-command, although it works in this case. It stops you being able to use my-fill-paragraph as a function to call from some other toggle. You should refactor the body to be (interactive)(funcall (setq this-command (if (eq last-command #'fill-paragraph) #'unfill-paragraph #'fill-paragraph))). I look forward to you adding the support for prefix arg to be passed on to fill-paragraph. – icarus Dec 31 '16 at 6:18
  • @icarus: (I didn't know about "@icarus's".) Edited as suggested (except using a symbol, not a function object, for this-command value). HTH. – Drew Dec 31 '16 at 17:30

Something like

(defun xuhdev/fill-paragraph ()
  (if (eq last-command this-command)

and then binding xuhdev/fill-paragraph to M-q perhaps? I can't say I am a great fan of the idea, and I am leaving off support for arguments to fill-paragraph...

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