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

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

[Sam Steingold]

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.

-- 
Sam Steingold (http://sds.podval.org/) on darwin Ns 10.3.1504
http://steingoldpsychology.com http://www.childpsy.net http://iris.org.il
https://ffii.org http://honestreporting.com http://islamexposedonline.com
If you cannot improve on silence, keep it.

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

[Ingo Lohmar]

On Thu, Mar 16 2017 13:20 (-0400), Sam Steingold wrote:
> --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---

Hi Sam,

AFAIK, you cannot use the (interactive "r") form for this "dwim-ish"
kind of behavior.  I find it easiest to just omit the arguments and the
interactive form, and then use (region-beginning) and (region-end) in
the function body.

If you want to be able to use the function non-interactively as well,
you could make the arguments optional and check for (or (beg
(use-region-p))).

HTH.

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

[Andreas Röhler]

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On 16.03.2017 19:31, Ingo Lohmar wrote:
> On Thu, Mar 16 2017 13:20 (-0400), Sam Steingold wrote:
>> --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---
> Hi Sam,
>
> AFAIK, you cannot use the (interactive "r") form for this "dwim-ish"
> kind of behavior.

Why that? If a region is set, why should (use-region-p) fail?

The answer is: there are contradictions in implementation.
Which was discussed at time.

Thanks Sam for showing that.




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

[Noam Postavsky]

On Fri, Mar 17, 2017 at 4:16 AM, Andreas Röhler
<andreas.roehler@online.de> wrote:
>>> --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---
>> AFAIK, you cannot use the (interactive "r") form for this "dwim-ish"
>> kind of behavior.
>
> Why that? If a region is set, why should (use-region-p) fail?

(use-region-p) doesn't fail, the "r" in interactive fails, when there
is no mark (i.e., when a region is not and has never been set). It's
basically equivalent to this:

(defun my-command (beg end)
  (interactive (sort (list (point) (mark)) #'<))
  (if (use-region-p)
      (my-command-region beg end)
    (my-command-non-region)))

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

[Andreas Röhler]

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On 17.03.2017 14:05, Noam Postavsky wrote:
> On Fri, Mar 17, 2017 at 4:16 AM, Andreas Röhler
> <andreas.roehler@online.de> wrote:
>>>> --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---
>>> AFAIK, you cannot use the (interactive "r") form for this "dwim-ish"
>>> kind of behavior.
>> Why that? If a region is set, why should (use-region-p) fail?
> (use-region-p) doesn't fail, the "r" in interactive fails, when there
> is no mark (i.e., when a region is not and has never been set). It's
> basically equivalent to this:
>
> (defun my-command (beg end)
>    (interactive (sort (list (point) (mark)) #'<))
>    (if (use-region-p)
>        (my-command-region beg end)
>      (my-command-non-region)))

Okay, thanks. So that's no occasion to question the use-region-p, 
region-active-p design.
For the case given, think the error is reasonable, as a command 
explicitly working on region might expect an existing one.




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

[Stefan Monnier]

> --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)))

I think this should be

    (defun my-command (beg end)
      (interactive
       (if (use-region-p) (list (region-beginning) (region-end))
         (lit something else)))
      ...)

IOW the command should depend on (use-region-p) but not the
function.


        Stefan