Path: utzoo!attcan!uunet!sco!seanf
From: seanf@sco.COM (Sean Fagan)
Newsgroups: comp.lang.fortran
Subject: Re: i++, i+=1, i=i+1
Message-ID: <1267@scolex>
Date: 16 Sep 88 19:45:57 GMT
References: <3976@h.cc.purdue.edu> <3659@lanl.gov>
Reply-To: seanf@sco.COM (Sean Fagan)
Organization: The Santa Cruz Operation, Inc.
Lines: 32

In article <3659@lanl.gov> jlg@lanl.gov (Jim Giles) writes:
>From article <3976@h.cc.purdue.edu>, by ags@h.cc.purdue.edu (Dave Seaman):
>> If you apply your preprocessor to 
>> 	x[i*f(j)+k*g(l)] += y
>> you get
>> 	x[i*f(j)+k*g(l)] = x[i*f(j)+k*g(l)] + y
>> which is not the same expression at all, becauses it causes the the subscript 
>> to be evaluated twice.
>
[functions not allowed to return different values on the same input]
[also not allowed to have side-effects]

Wrong.  They can.  Also, with regards to side-effects, a FORTRAN function
can modify a COMMON variable, or, happy happy, its argument.  So what
happens when j and l change between the first and second calls of f() and
g(), respectively?  Are you saying that the compiler can just optimize
(incorrectly, I should add) the function calls into one function call?
Which means that, in order to do what the programmer wants, he has to use
temporary variables?

Didn't I see an article a while ago saying that FORTRAN was nice because you
didn't have to use temporary variables to get what you wanted evaluated
correctly?

>J. Giles
>Los Alamos


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Sean Eric Fagan  | "Joy is in the ears that hear, not in the mouth that speaks"
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