RE: [External] : interactive to do `use-region-p'

[Drew Adams]

> > case of region/buffer-limit args, plus additional args.
> > (defun foo (beg end other)
> >   (interactive `(,@(dtrt) ,(+ 2 7)))
> >   ...)
> 
> You mean like this?
...
> (defun enum (&optional beg end suf)
>   "Enumerate each line from BEG to END, counting from one.
> Use SUF as a suffix to the digits inserted.
> BEG defaults to the beginning of the buffer,
> END defaults to the end of the buffer, and
> SUF defaults to \". \""
>   (interactive
>    `(,@(if (use-region-p)
>            (list (region-beginning) (region-end))
>          (list nil nil) )
>      ,(when current-prefix-arg
>         (read-string "suffix: ") )))
>   (or beg (setq beg (point-min)))
>   (or end (setq end (point-max)))
...

Sure, why not?
Or define that (if...) as a function and use that.