* (call-interactively FN) leaks prefix arg into FN when called from within an interactive command
@ 2018-04-24 1:05 Göktuğ Kayaalp
2018-04-24 13:21 ` Stefan Monnier
0 siblings, 1 reply; 3+ messages in thread
From: Göktuğ Kayaalp @ 2018-04-24 1:05 UTC (permalink / raw)
To: help-gnu-emacs
So, I have the following function:
,----
| (defun gk-find-file (arg)
| (interactive "P")
| (call-interactively (if arg #'find-file #'ffap)))
`----
bound to C-x C-f. That key sequence runs ffap, and with prefix argument
(i.e. C-u C-x C-f) it runs find-file. But that's not what I want, I
want the inverse, so I swap find-file and ffap:
,----
| (defun gk-find-file (arg)
| (interactive "P")
| (call-interactively (if arg #'ffap #'find-file)))
`----
but with this version, it always runs find file. After trying various
things I came up with this:
,----
| (defun gk-find-file (arg)
| (interactive "P")
| (if (null arg) (call-interactively #'find-file)
| (let (current-prefix-arg)
| (call-interactively #'ffap))))
`----
which worked as intended (yes I tried it w/o the let too). So the
prefix argument to gk-find-file leaks to ffap, causing it to think it
got a prefix argument too. Is this intentional, or a bug?
Nevertheless, this is really confusing. And reading "(elisp) Prefix
Command Arguments", it does not really indicate this:
,----
| -- Variable: current-prefix-arg
| This variable holds the raw prefix argument for the _current_
| command. Commands may examine it directly, but the usual method
| for accessing it is with ‘(interactive "P")’.
`----
This is a more generic example:
,----
| (defun foo (arg)
| (interactive "P")
| (call-interactively
| (lambda (arg)
| (interactive "P")
| (message "%S %S %S" arg current-prefix-arg prefix-arg))))
|
| M-x foo => nil nil nil
| C-u M-x foo => (4) (4) nil
`----
But is it really the _current_ command when it's invoked by
call-interactively? It was totally unexpected for me that the value of
current-prefix-arg leaks into a function F in (call-interactively F). I
believe call-interactively should be, at least optionally, able to
suppress the prefix arg from the context it was called in. Is this
expected behaviour? If so, why is it not documented?
--
İ. Göktuğ Kayaalp <https://www.gkayaalp.com/>
024C 30DD 597D 142B 49AC
40EB 465C D949 B101 2427
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: (call-interactively FN) leaks prefix arg into FN when called from within an interactive command
2018-04-24 1:05 (call-interactively FN) leaks prefix arg into FN when called from within an interactive command Göktuğ Kayaalp
@ 2018-04-24 13:21 ` Stefan Monnier
2018-04-24 14:10 ` Göktuğ Kayaalp
0 siblings, 1 reply; 3+ messages in thread
From: Stefan Monnier @ 2018-04-24 13:21 UTC (permalink / raw)
To: help-gnu-emacs
> | (if (null arg) (call-interactively #'find-file)
> | (let (current-prefix-arg)
> | (call-interactively #'ffap))))
> `----
I'd use
(let ((current-prefix-arg nil))
(call-interactively (if arg #'ffap #'find-file)))
> So the prefix argument to gk-find-file leaks to ffap,
The (interactive "P") does not *consume* the value of
current-prefix-arg, indeed. It just uses it to set the value of `arg`.
> Is this intentional, or a bug?
Neither. It's a consecuence of the design.
> But is it really the _current_ command when it's invoked by
> call-interactively?
The "current command" is defined in terms of read-eval-loop, not in
terms of `call-interactively`. For the same reason `call-interactively`
does not run pre-command-hook and post-command-hook.
Stefan
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: (call-interactively FN) leaks prefix arg into FN when called from within an interactive command
2018-04-24 13:21 ` Stefan Monnier
@ 2018-04-24 14:10 ` Göktuğ Kayaalp
0 siblings, 0 replies; 3+ messages in thread
From: Göktuğ Kayaalp @ 2018-04-24 14:10 UTC (permalink / raw)
To: Stefan Monnier; +Cc: help-gnu-emacs
On 2018-04-24 09:21 -04, Stefan Monnier <monnier@iro.umontreal.ca> wrote:
>> So the prefix argument to gk-find-file leaks to ffap,
>
> The (interactive "P") does not *consume* the value of
> current-prefix-arg, indeed. It just uses it to set the value of `arg`.
>
>> Is this intentional, or a bug?
>
> Neither. It's a consecuence of the design.
>
>> But is it really the _current_ command when it's invoked by
>> call-interactively?
>
> The "current command" is defined in terms of read-eval-loop, not in
> terms of `call-interactively`. For the same reason `call-interactively`
> does not run pre-command-hook and post-command-hook.
Thanks a lot for the explanation!
--
İ. Göktuğ Kayaalp <https://www.gkayaalp.com/>
024C 30DD 597D 142B 49AC
40EB 465C D949 B101 2427
^ permalink raw reply [flat|nested] 3+ messages in thread
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2018-04-24 1:05 (call-interactively FN) leaks prefix arg into FN when called from within an interactive command Göktuğ Kayaalp
2018-04-24 13:21 ` Stefan Monnier
2018-04-24 14:10 ` Göktuğ Kayaalp
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