From: Vincent Lefevre <vincent@vinc17.org>
To: Zsh hackers list <zsh-workers@sunsite.dk>
Cc: Peter Stephenson <p.w.stephenson@ntlworld.com>
Subject: Re: arithmetic operator precedence
Date: Mon, 16 Jun 2008 16:33:28 +0200 [thread overview]
Message-ID: <20080616143328.GY10734@prunille.vinc17.org> (raw)
In-Reply-To: <20080616135934.GD5091@sc.homeunix.net>
On 2008-06-16 14:59:34 +0100, Stephane Chazelas wrote:
> It's at least consistent with other shells and bc at the moment:
>
> ~$ bash -c 'echo $((-2**2))'
> 4
> ~$ zsh -c 'echo $((-2**2))'
> 4
> ~$ ksh93 -c 'echo $((-2**2))'
> 4
> ~$ echo '-2 ^ 2' | bc
> 4
That are almost the only ones.
> bc is one place where POSIX specifies the precedence of
> unary-minus vs power:
> http://www.opengroup.org/onlinepubs/009695399/utilities/bc.html
> minus has higher precedence than ^ which I have to say is more
> intuitive to me.
Most users find the other way more intuitive, as with conventional
math writing
2
-2 = -4
(and that's also the reason why ** is right-associative, whereas
most operations are left-associative).
> Having said that:
>
> ~$ perl -le 'print -2 ** 2'
> -4
> ~$ python -c 'print -2 ** 2'
> -4
> ~$ ruby -e 'print -2 ** 2'
> -4%
> ~$ gawk 'BEGIN {print -2 ** 2}'
> -4
and:
vin:~> calc -- '-2 ^ 2'
-4
vin:~> qalc '-2 ^ 2'
-(2^2) = -4
vin:~> wcalc '-2 ^ 2'
= -4
vin:~> echo '-2 ^ 2' | gp -q
-4
vin:~> echo '-2 ^ 2;' | maple -q
-4
vin:~> echo '-2 ^ 2; quit' | mupad -S
>> -2 ^ 2; quit
-4
--
Vincent Lefèvre <vincent@vinc17.org> - Web: <http://www.vinc17.org/>
100% accessible validated (X)HTML - Blog: <http://www.vinc17.org/blog/>
Work: CR INRIA - computer arithmetic / Arenaire project (LIP, ENS-Lyon)
next prev parent reply other threads:[~2008-06-16 14:33 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 [this message]
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
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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