From: Jay Belanger <jay.p.belanger@gmail.com>
To: emacs-devel@gnu.org
Cc: jay.p.belanger@gmail.com
Subject: Re: Calc: `*' binds more strongly than `/'
Date: Wed, 25 Apr 2007 15:54:36 -0500 [thread overview]
Message-ID: <87d51sqinn.fsf@gmail.com> (raw)
In-Reply-To: <f0obnu$gkh$2@sea.gmane.org> (Christian Schlauer's message of "Wed\, 25 Apr 2007 21\:56\:51 +0200")
Christian Schlauer <cs-muelleimer-rubbish.bin@arcor.de> writes:
> Jay Belanger <belanger@truman.edu> writes:
...
>> Well, I think that's the proper way of doing it; even though there are
>> rules for interpreting expressions like a*b/c*d, that doesn't mean
>> writing the expression that way is a good thing to do -- it's just bad
>> form. I don't think there is any difference between Calc's current
>> precedence rule and the more standard one for properly written
>> expressions.
>
> I did some more `research', and a*b/c*d is not bad form, and it is a
> properly written expression, see Wikipedia. Let me cite from
> <http://en.wikipedia.org/wiki/Order_of_operations#Examples_from_arithmetic>:
As I said, there are rules for interpreting the above expressions.
I also said that avoiding the parentheses is bad form; note that the
wikipedia article also says:
Proper use of parentheses and other grouping symbols
When restricted to using a straight text editor, parentheses (or
more generally "grouping symbols") must be used generously to make
up for the lack of graphics, like square root symbols. Here are some
rules for doing so:
1) Whenever there is a fraction formed with a slash, put the
numerator (the number on top of the fraction) in one set of
parentheses, and the denominator (the number on the bottom of the
fraction) in another set of parentheses. This is not required for
fractions formed with underlines:
y = (x+1)/(x+2)
...
5) An exception to the rules requiring parentheses applies when only
one character is present. While correct either way, it is more
readable if parentheses around a single character are omitted:
y = (3)/(x) or y = 3/x
y = (3)/(2x) or y = 3/(2x)
> So besides Excel, Gnumeric, MATLAB, all pocket calculators, Wikipedia
> agrees with me, too.
Well, wikipedia also says
Calculators
Different calculators follow different orders of operations.
and gives several examples.
The reason for Calc's current behavior is because Dave Gillespie,
Calc's author, thought of "a b / c d" as representing
a b
---
c d
To have it represent "a(b/c)d", the parentheses can (and, according to
wikipedia, should be) put in. For those that really don't like
parentheses, an option to allow the user to decide for themselves the
relative precedence of * and / in Calc will be added, of course.
Jay
next prev parent reply other threads:[~2007-04-25 20:54 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-04-14 11:57 Calc: `*' binds more strongly than `/' Christian Schlauer
2007-04-14 15:09 ` Jay Belanger
2007-04-15 19:21 ` Chong Yidong
2007-04-15 20:05 ` Stefan Monnier
2007-04-17 12:47 ` Randal L. Schwartz
2007-04-17 18:03 ` Stefan Monnier
2007-04-18 8:44 ` Kim F. Storm
2007-04-18 19:27 ` Stefan Monnier
2007-04-18 20:02 ` Davis Herring
2007-04-18 20:16 ` David Kastrup
2007-04-18 21:43 ` Davis Herring
2007-04-19 16:10 ` Stefan Monnier
2007-04-20 11:13 ` Randal L. Schwartz
2007-04-20 13:40 ` Stefan Monnier
2007-04-20 14:07 ` Jay Belanger
2007-04-22 1:31 ` Miles Bader
2007-04-22 10:19 ` Christian Schlauer
2007-04-22 10:23 ` Christian Schlauer
2007-04-22 19:47 ` Jay Belanger
2007-04-23 10:46 ` Jason Rumney
2007-04-23 13:03 ` Kim F. Storm
2007-04-23 15:54 ` Jay Belanger
2007-04-25 19:56 ` Christian Schlauer
2007-04-25 20:54 ` Jay Belanger [this message]
2007-04-26 3:35 ` Stefan Monnier
2007-04-26 4:06 ` Jay Belanger
2007-04-26 14:11 ` Stefan Monnier
2007-04-26 21:07 ` Christian Schlauer
2007-04-26 15:07 ` Davis Herring
2007-04-26 16:01 ` Stefan Monnier
2007-04-26 18:32 ` Luc Teirlinck
2007-04-26 21:29 ` Christian Schlauer
2007-04-26 23:17 ` Luc Teirlinck
2007-04-26 21:07 ` Christian Schlauer
2007-04-27 1:27 ` Jay Belanger
2007-04-26 17:47 ` Davis Herring
2007-06-20 15:23 ` Jay Belanger
2007-06-20 16:02 ` Kim F. Storm
2007-06-20 17:13 ` Jay Belanger
2007-06-20 17:29 ` Luc Teirlinck
2007-06-20 17:54 ` Jay Belanger
2007-06-20 19:14 ` Kim F. Storm
2007-06-20 19:28 ` Luc Teirlinck
2007-06-20 20:18 ` Jay Belanger
2007-04-17 18:54 ` Jay Belanger
2007-04-18 21:55 ` Christian Schlauer
2007-04-19 2:58 ` Daniel Brockman
2007-04-22 10:27 ` Christian Schlauer
2007-04-26 16:00 ` Daniel Brockman
2007-04-19 15:16 ` Drew Adams
2007-04-19 17:05 ` David Kastrup
2007-04-19 17:18 ` Drew Adams
2007-04-19 17:33 ` David Kastrup
2007-04-16 15:38 ` Richard Stallman
2007-04-17 12:47 ` Randal L. Schwartz
2007-04-18 21:29 ` Christian Schlauer
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