Path: utzoo!utgpu!water!watmath!clyde!att!rutgers!cmcl2!lanl!jlg
From: jlg@lanl.gov (Jim Giles)
Newsgroups: comp.lang.fortran
Subject: Re: Fortran versus C for numerical analysis
Message-ID: <3185@lanl.gov>
Date: 2 Sep 88 20:43:10 GMT
References: <344@quintus.UUCP>
Organization: Los Alamos National Laboratory
Lines: 26

From article <344@quintus.UUCP>, by ok@quintus.uucp (Richard A. O'Keefe):
> What I meant was that there is no method of saying "this grouping is
> just syntactic so that I can read the expression, mathematical laws may
> be applied".  The point is that some expressions can't be written
> without using parens, and there is no way of distinguishing those parens
> from ones that you *want* to have the special effect.  For example,
> unless I am mistaken, (1.0+X)*2.0 must be evaluated that way rather than
> as 2.0+2.0*X. Sometimes you care, but sometimes you don't.

This is what I meant when I said that parenthesis aren't necessarily
the _best_ way of doing this.  But _some_ method is needed.  In this
respect, Fortran beats C.

> [...]                                                       In This
> particular example, unless you want to do part of the calculation
> yourself, you have to put the parens in to get around the operator
> priorities.  If, however, I write 2*I+2, the compiler *is* free to
> rearrange this as 2*(I+1).  Isn't it?

YES!  Fortran _can_ optimize using the distributive rule in reverse.
Maybe what's needed is a new syntax which specifies meaning without
forcing order.  How about {A+B}*C, which the compiler would be allowed 
to implement as A*C+B*C.

J. Giles
Los Alamos