From: Andrew Hyatt <ahyatt@gmail.com>
To: rms@gnu.org
Cc: emacs-devel@gnu.org
Subject: Re: pcase defuns
Date: Sun, 17 Apr 2022 18:09:24 -0400 [thread overview]
Message-ID: <m235ibfjl7.fsf@andrews-mbp.lan> (raw)
In-Reply-To: <E1nZmOs-0002uf-Vj@fencepost.gnu.org>
On Thu, Mar 31, 2022 at 12:27 AM Richard Stallman <rms@gnu.org>
wrote:
> [[[ To any NSA and FBI agents reading my email: please consider
> ]]] [[[ whether defending the US Constitution against all
> enemies, ]]] [[[ foreign or domestic, requires you to follow
> Snowden's example. ]]]
>
> > 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)
next prev parent reply other threads:[~2022-04-17 22:09 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-19 4:53 pcase defuns Andrew Hyatt
2021-12-19 8:34 ` Tassilo Horn
2021-12-19 15:33 ` Andrew Hyatt
2021-12-19 17:16 ` Tassilo Horn
2021-12-19 19:05 ` Stefan Monnier
2021-12-20 5:56 ` Tassilo Horn
2021-12-22 14:07 ` LdBeth
2021-12-19 17:23 ` Stefan Monnier
2021-12-19 21:08 ` Andrew Hyatt
2021-12-21 4:15 ` Richard Stallman
2021-12-21 5:20 ` Andrew Hyatt
2021-12-22 4:18 ` Richard Stallman
2021-12-23 1:52 ` Andrew Hyatt
2021-12-24 4:13 ` Richard Stallman
2021-12-21 15:32 ` Stefan Monnier
2021-12-20 4:43 ` Richard Stallman
2021-12-23 2:30 ` Po Lu
2022-03-26 17:41 ` Andrew Hyatt
2022-03-27 9:31 ` Stefan Monnier
2022-03-27 18:17 ` Andrew Hyatt
2022-03-28 4:15 ` Richard Stallman
2022-03-30 1:28 ` Andrew Hyatt
2022-03-31 4:27 ` Richard Stallman
2022-04-17 22:09 ` Andrew Hyatt [this message]
2022-04-19 3:48 ` Richard Stallman
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