GNU bug report logs - #20643
24.5; Please improve documentation of `pcase-let'

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Philipp Stephani <p.stephani2 <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.5; Please improve documentation of `pcase-let'
Date: Sun, 24 May 2015 12:36:47 +0200

The documentation of `pcase-let' is very terse.  Please expand it to
state what happens to each binding in the case that the pattern of a
binding matches, in the case where it doesn't match, and in the case
where there are no binding constructs in a pattern.



In GNU Emacs 24.5.1 (x86_64-apple-darwin14.1.0, NS apple-appkit-1344.72)
 of 2015-04-12 on p
Configured using:
 `configure --prefix=/usr/local/Cellar/emacs/24.5
 --enable-locallisppath=/usr/local/share/emacs/site-lisp
 --infodir=/usr/local/Cellar/emacs/24.5/share/info/emacs
 --with-file-notification=gfile --with-dbus --with-gnutls --with-rsvg
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Message #8 received at 20643 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Philipp Stephani <p.stephani2 <at> gmail.com>
Cc: 20643 <at> debbugs.gnu.org
Subject: Re: bug#20643: 24.5; Please improve documentation of `pcase-let'
Date: Sun, 24 May 2015 22:39:47 -0400

> The documentation of `pcase-let' is very terse.  Please expand it to
> state what happens to each binding in the case that the pattern of a
> binding matches, in the case where it doesn't match, and in the case
> where there are no binding constructs in a pattern.

I added:

   The macro is expanded and optimized under the assumption that those
   patterns *will* match, so a mismatch may go undetected or may cause
   any kind of error."


-- Stefan

Message #11 received at 20643 <at> debbugs.gnu.org (full text, mbox):

From: Philipp Stephani <p.stephani2 <at> gmail.com>
To: Stefan Monnier <monnier <at> iro.umontreal.ca>
Cc: 20643 <at> debbugs.gnu.org
Subject: Re: bug#20643: 24.5; Please improve documentation of `pcase-let'
Date: Sun, 21 Jun 2015 13:10:13 +0000

[Message part 1 (text/plain, inline)]

Stefan Monnier <monnier <at> iro.umontreal.ca> schrieb am Mo., 25. Mai 2015 um
04:39 Uhr:

> > The documentation of `pcase-let' is very terse.  Please expand it to
> > state what happens to each binding in the case that the pattern of a
> > binding matches, in the case where it doesn't match, and in the case
> > where there are no binding constructs in a pattern.
>
> I added:
>
>    The macro is expanded and optimized under the assumption that those
>    patterns *will* match, so a mismatch may go undetected or may cause
>    any kind of error."
>
>
>
Thanks. Though I think it would be better to be more defensive and
guarantee to raise a signal in the case of a mismatch.

[Message part 2 (text/html, inline)]

Message #14 received at 20643 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Philipp Stephani <p.stephani2 <at> gmail.com>
Cc: 20643 <at> debbugs.gnu.org
Subject: Re: bug#20643: 24.5; Please improve documentation of `pcase-let'
Date: Sun, 21 Jun 2015 21:23:47 -0400

> Thanks. Though I think it would be better to be more defensive and
> guarantee to raise a signal in the case of a mismatch.

If you want that, you need to use pcase, or pcase-exclusive.

This is a judgment call, but it lets pcase-let generate significantly
shorter and more efficient code and hence better serve the expected
common case.


        Stefan

Message #19 received at 20643-quiet <at> debbugs.gnu.org (full text, mbox):

From: Noam Postavsky <npostavs <at> gmail.com>
To: 20643-quiet <at> debbugs.gnu.org
Subject: Re: bug#20643: 24.5; Please improve documentation of `pcase-let'
Date: Sun, 02 Sep 2018 11:13:52 -0400

tags 20643 fixed
close 20643 25.1
quit

Stefan Monnier <monnier <at> iro.umontreal.ca> writes:

> I added:
>
>    The macro is expanded and optimized under the assumption that those
>    patterns *will* match, so a mismatch may go undetected or may cause
>    any kind of error."

[1: dde09cdbce]: 2015-05-24 22:38:05 -0400
  * lisp/emacs-lisp/pcase.el: Use PAT rather than UPAT in docstring
  (pcase-let): Document the behavior in case the pattern doesn't match.
  https://git.savannah.gnu.org/cgit/emacs.git/commit/?id=dde09cdbce0239bba0248a8ed5c1f4d85c5e8476

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