Re: [Emacs-diffs] master b88e7c8: Make transpose-regions interactive (Bug#30343)

[Juri Linkov <juri@linkov.net>]

>> > Instead of defining transpose-regions (and its interactive spec) in
>> > Lisp (as the reverted patch did), we could take the current
>> > interactive spec of transpose-regions and use that to make a preloaded
>> > function named "read-two-regions" in simple.el.  That would allow its
>> > reuse by other commands, too.
>>
>> Where would such a function be useful?
>
> Nothing specific comes to mind.  There is one pair of commands that
> already reads multiple regions: ediff-regions-linewise and -wordwise,
> so it's not unlikely that there could be other applications.

Why not use a compromise and move only the interactive spec to simple.el:

(put 'transpose-regions
     'interactive-form
     '(if (< (length mark-ring) 2)
	  (error "Other region must be marked before transposing two regions")
	(let* ((num (if current-prefix-arg
			(prefix-numeric-value current-prefix-arg)
		      0))
	       (ring-length (length mark-ring))
	       (eltnum (mod num ring-length))
	       (eltnum2 (mod (1+ num) ring-length)))
	  (list (point) (mark) (elt mark-ring eltnum) (elt mark-ring eltnum2)))))