GNU bug report logs - #13678
24.2.93; pcase: mention list-like QPatterns in the doc

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

From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: bug-gnu-emacs <at> gnu.org
Subject: 24.2.93; pcase: mention list-like QPatterns in the doc
Date: Sun, 10 Feb 2013 18:49:33 +0100

Hi,

due to the doc of `pcase' (similarly in the manual), this is the list of
forms that is valid as a QPattern:

,----------------------------------------------------------------------
| QPatterns can take the following forms:
|   (QPAT1 . QPAT2)	matches if QPAT1 matches the car and QPAT2 the cdr.
|   ,UPAT			matches if the UPattern UPAT matches.
|   STRING		matches if the object is `equal' to STRING.
|   ATOM			matches if the object is `eq' to ATOM.
`----------------------------------------------------------------------

I think it should also mention list-like patterns (without dot):

    (QPat1 ...QPatn)    matches any n-element list were each
                        element matches the according QPattern

Sure, `(QPAT1 . QPAT2)' also matches lists - but `(QPAT1 . QPAT2)' and
`(QPat1 ...QPatn)' are different forms (expressions) (although those
expressions could match equal values), so IMHO both should be mentioned.


Thanks,

Michael.


In GNU Emacs 24.2.93.1 (x86_64-unknown-linux-gnu, GTK+ Version 2.24.10)
 of 2013-02-09 on drachen
Bzr revision: cyd <at> gnu.org-20130209044342-t2b063zu2fqy8nud
Windowing system distributor `The X.Org Foundation', version 11.0.10707000
System Description:	Debian GNU/Linux 7.0 (wheezy)

Configured using:
 `configure '--prefix=/usr/local/built/''

Message #8 received at 13678 <at> debbugs.gnu.org (full text, mbox):

From: Stefan Monnier <monnier <at> iro.umontreal.ca>
To: Michael Heerdegen <michael_heerdegen <at> web.de>
Cc: 13678 <at> debbugs.gnu.org
Subject: Re: bug#13678: 24.2.93; pcase: mention list-like QPatterns in the doc
Date: Sun, 10 Feb 2013 20:43:57 -0500

> Sure, `(QPAT1 . QPAT2)' also matches lists - but `(QPAT1 . QPAT2)' and
> `(QPat1 ...QPatn)' are different forms (expressions)

Actually, no, they are identical:

  (QPAT1 QPAT2 QPAT3) is indistinguishable from
  (QPAT1 . (QPAT2 . (QPAT3 . nil)))

the equivalence between the two is imposed by the reader, long before we
know that these things will be "patterns in a pcase" rather than
expressions, or data in a quoted thingy, ...
  

        Stefan

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

From: Michael Heerdegen <michael_heerdegen <at> web.de>
To: bug-gnu-emacs <at> gnu.org
Subject: Re: bug#13678: 24.2.93; pcase: mention list-like QPatterns in the doc
Date: Mon, 11 Feb 2013 14:37:48 +0100

Hi Stefan,

> > Sure, `(QPAT1 . QPAT2)' also matches lists - but `(QPAT1 . QPAT2)' and
> > `(QPat1 ...QPatn)' are different forms (expressions)
>
> Actually, no, they are identical:
>
>   (QPAT1 QPAT2 QPAT3) is indistinguishable from
>   (QPAT1 . (QPAT2 . (QPAT3 . nil)))
>
> the equivalence between the two is imposed by the reader, long before we
> know that these things will be "patterns in a pcase" rather than
> expressions, or data in a quoted thingy, ...

Simply right, thanks.  I wonder, however, if that's clear for every
user.  Nonetheless, there are enough examples in

  (elisp) Pattern matching case statement

that use the (QPAT1 QPAT2 QPAT3) syntax.  So, I'll close this, thanks.


Regards,

Michael.

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