From: Stephane Chazelas <Stephane_Chazelas@yahoo.fr>
To: Zsh hackers list <zsh-workers@sunsite.dk>,
Richard Hartmann <richih.mailinglist@gmail.com>,
Peter Stephenson <p.w.stephenson@ntlworld.com>
Subject: Re: arithmetic operator precedence
Date: Tue, 17 Jun 2008 13:46:07 +0100 [thread overview]
Message-ID: <20080617124607.GH5016@sc.homeunix.net> (raw)
In-Reply-To: <20080617123551.GJ10734@prunille.vinc17.org>
On Tue, Jun 17, 2008 at 02:35:51PM +0200, Vincent Lefevre wrote:
[...]
> But POSIX does not say that variable expansion should be performed
> before the arithmetic expression (at least in th way you think).
> If POSIX said so, then with a="1 + 1", $((a * 3)) would give
> $((1 + 1 * 3)) after variable expansion (without being able to make
> the difference with $((1 + 1 * 3)) written directly), then 5 after
> arithmetic expansion. But neither zsh nor bash behaves in that way.
[...]
$((a * 3)) is unspecified as per POSIX if $a doesn't contain an
integer constant. That was my point.
If $a contains an integer constant such as -3, then as per
POSIX, $((a * 3)) should be the same as $(($a * 3)), that is
$((-3 * 3)). If we extend that to the non-POSIX **, that would
be:
a=-3; $((a ** 2)) should be the same as $((-3 ** 2)).
So, if a future version of POSIX adds a **, it is bound to
specify it as $((-3 ** 2)) == 9 if it wants to keep consistant.
That would even be in accordance with all the existing shell
implementations that have **.
So, I think that with SH_PRECEDENCE, $((-3 ** 2)) should give 9.
--
Stéphane
next prev parent reply other threads:[~2008-06-17 12:46 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-06-12 9:57 Stephane Chazelas
2008-06-12 13:12 ` Mikael Magnusson
2008-06-12 13:40 ` Peter Stephenson
2008-06-12 14:47 ` Bart Schaefer
2008-06-12 15:01 ` Stephane Chazelas
2008-06-16 8:17 ` Vincent Lefevre
2008-06-16 8:07 ` Vincent Lefevre
2008-06-16 13:42 ` Peter Stephenson
2008-06-16 13:59 ` Stephane Chazelas
2008-06-16 14:33 ` Vincent Lefevre
2008-06-17 9:19 ` Richard Hartmann
2008-06-17 9:45 ` Stephane Chazelas
2008-06-17 10:24 ` Richard Hartmann
2008-06-17 10:24 ` Richard Hartmann
2008-06-17 10:38 ` Stephane Chazelas
2008-06-17 10:43 ` Peter Stephenson
2008-06-17 11:28 ` Vincent Lefevre
2008-06-17 11:46 ` Peter Stephenson
2008-06-17 12:05 ` Vincent Lefevre
2008-06-19 9:37 ` Jun T.
2008-06-19 9:54 ` Stephane Chazelas
2008-06-19 16:00 ` Vincent Lefevre
2008-06-19 16:20 ` Stephane Chazelas
2008-06-19 17:14 ` Vincent Lefevre
2008-06-19 9:58 ` Peter Stephenson
2008-06-19 12:29 ` Richard Hartmann
2008-06-19 16:04 ` Vincent Lefevre
2008-06-19 16:10 ` Mikael Magnusson
2008-06-19 16:27 ` Stephane Chazelas
2008-06-19 17:25 ` Vincent Lefevre
2008-06-19 17:20 ` Vincent Lefevre
2008-06-17 10:45 ` Richard Hartmann
2008-06-17 11:38 ` Vincent Lefevre
2008-06-17 11:19 ` Vincent Lefevre
2008-06-17 11:57 ` Stephane Chazelas
2008-06-17 12:35 ` Vincent Lefevre
2008-06-17 12:46 ` Stephane Chazelas [this message]
2008-06-17 13:02 ` Vincent Lefevre
2008-06-17 13:20 ` Stephane Chazelas
2008-06-17 14:33 ` Vincent Lefevre
2008-06-17 14:53 ` Stephane Chazelas
2008-06-17 15:49 ` Vincent Lefevre
2008-06-17 14:35 ` Stephane Chazelas
2008-06-17 15:05 ` Vincent Lefevre
2008-06-17 10:54 ` Vincent Lefevre
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