Re: elisp exercise: toggle-letter-case

[Andreas Politz <politza@fh-trier.de>]

Xah wrote:
> here's a little interesting exercise.
> 
> I'm writing a toggle-letter-case function below. However, it has some
> problems. (see the doc string). After thinking on this for a while,
> the problem seems a bit complex. It'll take perhaps few hours to fix
> these, in particular, if it is to cover chars like éÉ èÈ üÜ. Also, it
> seems a good solution will require this function to have a state, but
> i'm reluctant to introduce a global variable for it.
> 
> I'm wondering, if anyone have a better solution?
> 
> (defun toggle-letter-case ()
>   "Toggle the letter case of current word or text selection.
> Toggles from 3 cases: upper case, lower case, title case,
> in that order.
> Title case means upcase first letter of each word.
> 
> Todo:
> • this command only consider English alphabets. For example, it may
> not work properly if you have éÉ èÈ üÜ.
> • It may not work when the first or second letter is a number, e.g.
> “1time”.
> • It may not work when you only have a single letter. e.g. “A
> teapot”."
> (interactive)
> 
> (save-excursion
> (let (pt pos1 pos2 cap1p cap2p (deactivate-mark nil) (case-fold-search
> nil)
>          )
>   (setq pt (point))
>   (if (and transient-mark-mode mark-active)
>       (setq pos1 (region-beginning)
>             pos2 (region-end))
>     (setq pos1 (car (bounds-of-thing-at-point 'word))
>           pos2 (cdr (bounds-of-thing-at-point 'word))))
> 
> ;; check 1th and 2th letters cases
>   (goto-char pos1)
>   (setq cap1p (looking-at "[A-Z]"))
>   (goto-char (1+ pos1))
>   (setq cap2p (looking-at "[A-Z]"))
> 
>   (cond
>    ((and (not cap1p) (not cap2p)) (upcase-initials-region pos1 pos2))
>    ((and cap1p (not cap2p)) (upcase-region pos1 pos2) )
>    ((and cap1p cap2p) (downcase-region pos1 pos2) )
>    (t (downcase-region pos1 pos2) )
>    )
>   )
> )
> )
> 
> PS the above assumes you have transient-mode on.
> 
>   Xah
> ∑ http://xahlee.org/
> 
> ☄


Giving the command a state makes it so much easier, because you
don't have to look at the text at all.  Unless you want it to
consider the current textstate.
Anyway, here is how I would do it:
					
(defun up/down/camel-case (&optional start end)
   (interactive (if (and transient-mark-mode mark-active)
		   (list (region-beginning)
			 (region-end))))

   (if (not (eq last-command this-command))
       (put this-command 'call-count 0))
   (let* ((mark (and transient-mark-mode mark-active))
	(call-count (get this-command 'call-count))
	deactivate-mark
	(action
	 (nth call-count
	      (if mark
		  '(downcase-region upcase-region capitalize-region)
		'(downcase-word upcase-word capitalize-word)))))
     (if mark
	(apply action (list start end))
       (funcall action 1)
       (backward-word))
     (put this-command 'call-count (% (1+ call-count) 3))))

-ap