Path: utzoo!utgpu!attcan!uunet!garfield!john13
From: john13@garfield.MUN.EDU (John Russell)
Newsgroups: comp.lang.c
Subject: Re: Unnecessary Macros (was Re: Unnecessary Parenthesis)
Message-ID: <4920@garfield.MUN.EDU>
Date: 10 Oct 88 23:54:06 GMT
References: <2089@ssc-vax.UUCP> <441@kaon.uchicago.edu> <1527@devsys.oakhill.UUCP>
Reply-To: john13@garfield.UUCP (John Russell)
Organization: Memorial University of Newfoundland
Lines: 29

In article <1527@devsys.oakhill.UUCP> steve@oakhill.UUCP (steve) writes:
><1401@devsys.oakhill.UUCP> <8629@smoke.ARPA>
>As I pointed out at that time, the use of temp was not optimal.  The two
>big draw backs are :
>  1) It is inefficient. 
>  2) the use of a temp which must be supplied.  

How about this for an addition to C: a special keyword, similar to const,
which declares that a function which is passed identical values will always
return the same value, and that the function has no side effects.

Example:

consistent double cos();

#define square(x) ((x) * (x))

a = PI / 2.0;
b = square(cos(a));

The compiler knows "a" does not change in the expanded expression, so it uses
its own temp and only calls cos once.

Is this feasible? Doesn't sound too hard...

John
-- 
"...and intuition, in a case such as this, is of crucial importance."
			-- William Gibson, _Count_Zero_