GNU bug report logs - #914
In CVS Emacs, calc-eval gives multiplication higher precedence than division

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Message #5 received at submit <at> emacsbugs.donarmstrong.com (full text, mbox):

From: Francis Litterio <flitterio <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org, emacs-devel <at> gnu.org
Subject: In CVS Emacs, calc-eval gives multiplication higher precidence than division
Date: Sun, 07 Sep 2008 12:06:38 -0400

In CVS Emacs, function calc-eval (in lisp/calc/calc.el) gives
multiplication higher precidence than division.  To reproduce, run
"emacs -q" and evaluate this form:

   (progn
     (require 'calc)
     (calc-eval "1 / 2 * 1000"))

The value of the above form is "5e-4" (as if operator '*' has higher
precidence than operator '/'), but it should be "500".
--
Fran

Message #16 received at 914 <at> emacsbugs.donarmstrong.com (full text, mbox):

From: "Lennart Borgman (gmail)" <lennart.borgman <at> gmail.com>
To: "Randal L. Schwartz" <merlyn <at> stonehenge.com>
Cc: Carsten Dominik <carsten.dominik <at> gmail.com>,
        914 <at> debbugs.gnu.org, emacs-devel <at> gnu.org
Subject: Re: In CVS Emacs, calc-eval gives multiplication higher  precidence
  than division
Date: Mon, 08 Sep 2008 22:53:54 +0200

Randal L. Schwartz wrote:
>>>>>> "Lennart" == Lennart Borgman (gmail) <lennart.borgman <at> gmail.com> writes:
> 
> Lennart> Of course I can see that the behaviour you want saves you a lot of key
> Lennart> strokes. My question is really about the default value. You can easily
> Lennart> change that, of course. The question is really if you prefer the old
> Lennart> default and in that case what arguments you want to present for that.
> 
> There's no need to change the longstanding defaults, because it would break
> things.  You already have a knob you can tweak if you think that "2 a / 3 b"
> should multiply by b, rather than divide by it.  That's a personal choice.

I think communication can be very difficult if you have too much
personal choice in it. Math is about communication (for a special class
of logical problems).

The original bug report was about this

  (calc-eval "1 / 2 * 1000")

Calc treats this as 1 / (2 * 1000) which is just plain wrong. I have
never seen a mathematician treat it that way - though I have seen many
pupils doing that.


> Frankly, I'd never touch that knob, because it looks to me like it should
> divide by b.  And I think most mathemeticians would agree, and that's the
> target for that part of Calc.  Stop thinking computer science.  Think
> *math* notation.

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