(interactive "r") and (use-region-p)

[Sam Steingold <sds@gnu.org>]

Hi

Is this a valid coding pattern:

--8<---------------cut here---------------start------------->8---
(defun my-command (beg end)
  (interactive "r")
  (if (use-region-p)
      (my-command-region beg end)
    (my-command-non-region)))
--8<---------------cut here---------------end--------------->8---

Alas, it fails with

(error "The mark is not set now, so there is no region")

when the mark is not set, instead of calling `my-command-non-region'.

What is the correct metaphor/pattern?

Maybe we should add "R" interactive code which would pass nil/nil if
`use-region-p' returns nil?

Thanks.

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Sam Steingold (http://sds.podval.org/) on darwin Ns 10.3.1504
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