From: Thierry Volpiatto <thierry.volpiatto@gmail.com>
To: emacs-devel@gnu.org
Subject: Re: pcase-dolist
Date: Thu, 09 Jul 2015 11:55:29 +0200 [thread overview]
Message-ID: <874mldwt7y.fsf@gmail.com> (raw)
In-Reply-To: 87oajlyif9.fsf@gnu.org
Tassilo Horn <tsdh@gnu.org> writes:
> Stefan Monnier <monnier@iro.umontreal.ca> writes:
>
>>> (pcase-let ((`(,w ,x ,y ,z) '(1 2 3)))
>>> (message "%s %s %s %s" w x y z))
>>
>>> prints "1 2 3 nil" although the pattern when used in `pcase' wouldn't
>>> match that list but only 4-element lists. So a pcase pattern has
>>> different semantics depending on whether it is used in `pcase' or
>>> `pcase-let' or `pcase-dolist' which doesn't feel right.
>>
>>> I'd prefer if `pcase-let' would signal an error if some pattern doesn't
>>> match.
>>
>> So you'd want the above to signal an error in the case of:
>>
>> (pcase-let ((`(,w ,x) '(1 2 3)))
>> (message "%s %s" w x))
>>
>> ?
>
> Yes, if you want to pick the first two elements of a list with 2 or more
> elements, you should use `(,w ,x . ,_). I see that the above is
> slightly more convenient and concise but I'd value consistency more.
This would be a regression IMHO, what if you want to do e.g:
(pcase-let ((`(,a ,b) (file-attributes "foo")))
(list a b))
It would be inconvenient to have to bind the 10 unused remaining elements.
Of course one can use `cl-multiple-value-bind' instead in such situation.
--
Thierry
Get my Gnupg key:
gpg --keyserver pgp.mit.edu --recv-keys 59F29997
next prev parent reply other threads:[~2015-07-09 9:55 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-08 12:20 pcase-dolist Michael Heerdegen
2015-07-08 13:54 ` pcase-dolist Stefan Monnier
2015-07-08 17:32 ` pcase-dolist Michael Heerdegen
2015-07-08 18:26 ` pcase-dolist Tassilo Horn
2015-07-08 21:27 ` pcase-dolist Stefan Monnier
2015-07-09 6:05 ` pcase-dolist Tassilo Horn
2015-07-09 9:55 ` Thierry Volpiatto [this message]
2015-07-09 10:17 ` pcase-dolist Tassilo Horn
2015-07-09 12:19 ` pcase-dolist Thierry Volpiatto
2015-07-09 13:34 ` pcase-dolist Tassilo Horn
2015-07-09 13:40 ` pcase-dolist Thierry Volpiatto
2015-07-09 19:26 ` pcase-dolist Stefan Monnier
2015-07-09 20:27 ` pcase-dolist Michael Heerdegen
2015-07-10 18:51 ` pcase-dolist Stefan Monnier
2015-10-12 11:27 ` pcase-setq (was: pcase-dolist) Michael Heerdegen
2015-10-12 11:54 ` pcase-setq Michael Heerdegen
2015-10-12 12:01 ` pcase-setq (was: pcase-dolist) Nicolas Petton
2015-10-12 12:36 ` pcase-setq Michael Heerdegen
2015-10-12 12:49 ` Semantic of pcase `seq' and `map' patterns (was: pcase-setq) Michael Heerdegen
2015-10-12 13:41 ` Semantic of pcase `seq' and `map' patterns Michael Heerdegen
2015-10-12 13:55 ` Nicolas Petton
2015-10-12 14:02 ` Michael Heerdegen
2015-10-17 12:21 ` Michael Heerdegen
2015-10-17 13:31 ` Nicolas Petton
2015-10-12 13:50 ` Semantic of pcase `seq' and `map' patterns (was: pcase-setq) Nicolas Petton
2015-10-13 0:59 ` pcase-setq Stefan Monnier
2015-10-13 13:52 ` pcase-setq Michael Heerdegen
2015-10-13 14:02 ` pcase-setq Michael Heerdegen
2015-10-13 15:52 ` pcase-setq Michael Heerdegen
[not found] ` <jwvfv1eboo8.fsf-monnier+emacs@gnu.org>
[not found] ` <87d1wh36as.fsf@web.de>
2015-10-14 15:49 ` pcase-setq Stefan Monnier
2015-07-10 14:44 ` pcase-dolist Tassilo Horn
2015-07-10 19:04 ` pcase-dolist Stefan Monnier
2015-07-08 19:44 ` pcase-dolist Artur Malabarba
2015-07-08 20:50 ` pcase-dolist Michael Heerdegen
-- strict thread matches above, loose matches on Subject: below --
2014-07-11 10:35 pcase-dolist Sebastian Wiesner
2014-07-11 13:47 ` pcase-dolist Stefan Monnier
2014-07-11 13:50 ` pcase-dolist Sebastian Wiesner
2014-07-11 14:14 ` pcase-dolist Stefan Monnier
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