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Re: Calc: `*' binds more strongly than `/'

From: Luc Teirlinck
Subject: Re: Calc: `*' binds more strongly than `/'
Date: Wed, 20 Jun 2007 14:28:45 -0500 (CDT)

Jay Belanger wrote:

   I can't offhand; that's what I asked about.

It can never make any difference in an expression containing only *
and /.

Indeed, what happens with equal precedence and left associativity in
an expression without parentheses containing only * and / is that any
`* a' (`/ a'. resp.) anywhere in the expression results in the final
result being bigger by (smaller by, resp.) a factor of a.  Giving /
higher precedence results in exactly the same.

Things do make a difference if a third "multiplicative type operator",
say mod, is involved.  If you give / and * equal precedence, then you
can be consistent and give these other ones exactly the same
precedence, and use left associativity (this is exactly what most
mathematical software I know of does with `mod', _unless_ they
_require_, as many do, explicit parentheses do disambiguate and throw
an error if these parentheses are missing).  But if you give / higher
precedence than *. then you have to decide which relative precedence
these other operators get.  Of course, that same problem occurs just
as much if you give * higher precedence than /, as Calc did up to know
and still does by default now (unless I misunderstood).

I do not know what preference Calc gives to mod, relative to / and *,
for either value of `calc-multiplication-has-precedence'.



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