From: Stephane Chazelas <Stephane_Chazelas@yahoo.fr>
To: "Jun T." <takimoto-j@kba.biglobe.ne.jp>
Cc: zsh-workers@sunsite.dk
Subject: Re: arithmetic operator precedence
Date: Thu, 19 Jun 2008 10:54:54 +0100 [thread overview]
Message-ID: <20080619095454.GE5016@sc.homeunix.net> (raw)
In-Reply-To: <a0600102dc47fd2c6184e@kba.biglobe.ne.jp>
On Thu, Jun 19, 2008 at 06:37:17PM +0900, Jun T. wrote:
>
> At 0:46 PM +0100 08.6.17, Peter Stephenson wrote:
> >As it looks like "some sort of"
> >compatibility might as well be with other shells (so the option could
> >really be called "SH_PRECEDENCES", although it's perhaps less obvious that
> >means "something approximating to the precedences you probably expect if
> >you are a regular programmer") this doesn't give us room for manoeuvre
> >without yet another option.
>
> -3**2 = 9 is quite counter-intuitive and "mathematically wrong",
[...]
I don't find it counter-intuitive nor mathematically wrong as
there's no "**" operator of that shape in "maths".
But to rephrase what I was trying to say rather awkwardly
before.
With all the existing operators, one can do
x=$(( some-expression ))
y=$(( some-other-expression ))
z=$(( $x <op> $y ))
and it's OK whatever some-expression and some-other-expression
and <op> as long as they are POSIX.
The syntax above is the only one you can write in a POSIX
script, and POSIX guarantees it to work at the moment.
If you change ** so that it has higher precedence than the
unary minus, you break that harmony.
Typically, that means you'll have to write:
z=$(( ($x) <op> ($y) ))
because you now have operators that have higher precedence than
the unary "-" and unary "+".
Again ** is not a POSIX operator, so it's not really a concern
at this time, as you can't use ** in a POSIX script anyway. But
that's to show how it could become one if POSIX was to include
"**" in a future version of the standard and set its precedence
as you suggest.
--
Stéphane
next prev parent reply other threads:[~2008-06-19 9:55 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 [this message]
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20080619095454.GE5016@sc.homeunix.net \
--to=stephane_chazelas@yahoo.fr \
--cc=takimoto-j@kba.biglobe.ne.jp \
--cc=zsh-workers@sunsite.dk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://git.vuxu.org/mirror/zsh/
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).