Stefan Monnier <[EMAIL PROTECTED]> wrote on Fri, 18 Feb 2005
08:59:24 -0500:
>> Is it possible to determine at run time how many parameters an elisp
>> function takes? For example, I'd like to write something like:
>> (how-many-params 'null)
>> and have it evaluate to 1. Or something like that. Together with
>> some reasonable convention for indicating &optional and &rest
>> arguments.
> Why do you want to know?
I'd like to fix `beginning-of-defun-raw', where it does (funcall
beginning-of-defun-function). The parameter `arg' from
beginning-of-defun should be passed through to b-o-d-f. We've talked
about this before. Unfortunately, there is no guarantee that existing
user supplied functions can accept an `arg'. I would thus replace the
call with
(if (>= (how-many-params beginnin-of-defun-function) 1)
(funcall beginning-of-defun-function arg)
(funcall beginning-of-defun-function))
> Every time this has shown up for me, what I truly wanted to know was
> more like "can I call this with 4 args?", and the reason why I wanted
> to know was to know whether to call it with 4 args or otherwise do
> something else (e.g. call it with fewer args).
Exactly.
> In practice, it's simpler to just do
> (condition-case nil
> (fooo)
> (wrong-number-of-arguments
> (bar)))
> It's not perfect, but I've found it to suffer from fewer problems than
> other solutions. It's also faster.
Good idea!
Why is there not such a function in the Emacs core? It seems such an
incredibly useful function, say for debuggers or code-analysers, or for
the uses mentioned above. Did somebody just overlook it in the early
days, perhaps?
> Stefan
--
Alan Mackenzie (Munich, Germany)
Email: [EMAIL PROTECTED]; to decode, wherever there is a repeated letter
(like "aa"), remove half of them (leaving, say, "a").
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