Calling function as if it had a C-u prefix

Calling function as if it had a C-u prefix

[Tory S. Anderson]

I'm playing around with hydra and am trying to bind a key to do the equivalent of `C-u org-clock-in`. I've tried following a related question on SO[1] but it doesn't seem to be working. Can anyone tell me where I'm off? 

--8<---------------cut here---------------start------------->8---
(global-set-key
 (kbd "C-c o")
 (defhydra hydra-org-time-management (:color blue)
   "Org"
   ("w" (let ((current-prefix-arg 4)) (org-clock-in)) "clock-in")))
--8<---------------cut here---------------end--------------->8---

Footnotes: 
[1] http://stackoverflow.com/questions/12827887/emacs-universal-argument-c-u-in-a-function

RE: Calling function as if it had a C-u prefix

[Drew Adams]

> I'm playing around with hydra and am trying to bind a key to do the
> equivalent of `C-u org-clock-in`. I've tried following a related question on
> SO[1] but it doesn't seem to be working. Can anyone tell me where I'm off?

Call `org-clock-in' passing it an explicit argument that corresponds to
the prefix arg value.  (I don't have the function info, but if you do
`C-h f' you should see what the signature is.)

Sometimes a function does not pass the prefix arg as a parameter, but
typically functions do, and the advice above should be sufficient.

Re: Calling function as if it had a C-u prefix

[Michael Heerdegen]

Drew Adams <drew.adams@oracle.com> writes:

> Sometimes a function does not pass the prefix arg as a parameter, but
> typically functions do, and the advice above should be sufficient.

Should work.  `org-clock-in' uses (interactive "P"), so

    (org-clock-in '(4))

should do it.

Re: Calling function as if it had a C-u prefix

[Tory S. Anderson]

Ah, that did it! I had already tried both

    (org-clock-in t)
and
    (org-clock-in 4)

And they didn't do the trick. For whatever reason, the quote and the parentheses did the trick. Thanks!

Michael Heerdegen <michael_heerdegen@web.de> writes:

> Drew Adams <drew.adams@oracle.com> writes:
>
>> Sometimes a function does not pass the prefix arg as a parameter, but
>> typically functions do, and the advice above should be sufficient.
>
> Should work.  `org-clock-in' uses (interactive "P"), so
>
>     (org-clock-in '(4))
>
> should do it.

Re: Calling function as if it had a C-u prefix

[Michael Heerdegen]

torys.anderson@gmail.com (Tory S. Anderson) writes:

> For whatever reason, the quote and the
> parentheses did the trick. Thanks!

See (info "(elisp) Prefix Command Arguments").

One has to look at the interactive spec of the defun in the source to
see whether a numeric or raw prefix arg is used and expected in the
body.

When `org-clock-in' had used (interactive "p") instead, your version

    (org-clock-in 4)

would have worked.  But the function wants to treat a C-u prefix
specially, so it uses "P".

Re: Calling function as if it had a C-u prefix

[Emanuel Berg]

torys.anderson@gmail.com (Tory S. Anderson) writes:

> I'm playing around with hydra and am trying to bind
> a key to do the equivalent of `C-u org-clock-in`.
> I've tried following a related question on SO[1] but
> it doesn't seem to be working. Can anyone tell me
> where I'm off?

I don't have hydra (?) or `org-clock-in' but usually
those functions have an optional argument. For
example, the docstring of `forward-char':

    (forward-char &optional N)

In such a case, simply put an invocation with an
explicit argument in a wrapper (an interactive defun)
and bind that to the desired command (shortcut).

If you cannot use the optional argument try this:

    (defun forward-fourteen ()
      (interactive)
      (let ((current-prefix-arg 14))
        (call-interactively 'forward-char) ))

    (forward-fourteen) ; evaluate me and see how far

    (global-set-key "\C-x\M-o" 'forward-fourteen)

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underground experts united