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Re: pcase defuns
From: |
Andrew Hyatt |
Subject: |
Re: pcase defuns |
Date: |
Sun, 17 Apr 2022 18:09:24 -0400 |
On Thu, Mar 31, 2022 at 12:27 AM Richard Stallman <rms@gnu.org>
wrote:
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> The way I look at it, it does do this, but it's just
> structured differently. The normal defun as one arglist.
> Mine has one per matching clause, which means that it can
> take a variety of different arguments, all matching. And
> the arglist and the matching clauses are the same thing, so
> the arglist can be (n), or ('foo n), or (1 2 (3 n)), etc.
> Yes, it's weird, but I think the differentiation here is
> useful, see my next point.
The argument list is not just a concept in users' minds. The
command C-h f, which shows documentation for a function,
displays the function's argument list. If you try C-h f cons
RET, you'll see what I mean.
See also `func-arity'.
So there is a practical reason for defining constructs to set up
the function's argument list.
> In particular, with your proposal, we lose the ability to
> have fairly different arg patterns, with different numbers
> of args, or different destructuring patterns.
Not necessarily. You could specify `&rest args' for an arglist
that conveys no information. But users find it useful to see in
a simple way what the arguments of the function should be.
Thanks for the suggestion. I've implemented a new version along
the lines you suggested. So now things look like:
(defun-pattern fibonacci (n)
"Compute the fibonacci sequence."
(0 0)
(1 1)
(n
(+ (fibonacci (- n 1))
(fibonacci (- n 2)))))
and
(defun-pattern repeatedp (&rest args)
"Test for repeated pattern, returns nil, 'once, or 'twice, or
'split."
((a a) 'once)
((a a a) 'twice)
((a b a) 'split))
With this, I think I've answered your objections. Do you have an
opinion on what I should do with this? I can check this in the emacs
source code, as a GNU elpa package, or just put it in an external repository.
--
Dr Richard Stallman (https://stallman.org)
Chief GNUisance of the GNU Project (https://gnu.org)
Founder, Free Software Foundation (https://fsf.org)
Internet Hall-of-Famer (https://internethalloffame.org)
- Re: pcase defuns,
Andrew Hyatt <=