From: Stephane Chazelas <Stephane_Chazelas@yahoo.fr>
To: Peter Stephenson <p.w.stephenson@ntlworld.com>
Cc: Zsh hackers list <zsh-workers@sunsite.dk>
Subject: Re: arithmetic operator precedence
Date: Mon, 16 Jun 2008 14:59:34 +0100 [thread overview]
Message-ID: <20080616135934.GD5091@sc.homeunix.net> (raw)
In-Reply-To: <20080616144211.276fb0e3@pws-pc>
On Mon, Jun 16, 2008 at 02:42:11PM +0100, Peter Stephenson wrote:
> On Mon, 16 Jun 2008 10:07:26 +0200
> Vincent Lefevre <vincent@vinc17.org> wrote:
> > Speaking of precedence, the following one is nasty:
> >
> > vin% zsh -c 'echo $((-3**2))'
> > 9
> > vin% bash -c 'echo $((-3**2))'
> > 9
> > vin% ksh93 -c 'echo $((-3**2))'
> > 9
> >
> > IMHO these shells should be fixed to give -9, i.e. ** should have
> > the precedence over the unary -, like conventional math writing.
>
> That's an interesting point for C_PRECEDENCES since I was trying to get
> it behave as much as possible like Perl. What does anyone else think?
[...]
It's at least consistent with other shells and bc at the moment:
~$ bash -c 'echo $((-2**2))'
4
~$ zsh -c 'echo $((-2**2))'
4
~$ ksh93 -c 'echo $((-2**2))'
4
~$ echo '-2 ^ 2' | bc
4
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.
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
TCL has pow(x, y) instead of an operator.
--
Stéphane
next prev parent reply other threads:[~2008-06-16 13:59 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 [this message]
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
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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