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From: gateley@mips.csc.ti.com (John Gateley)
Newsgroups: comp.lang.c
Subject: Re: Unnecessary Macros (was Re: Unnecessary Parenthesis)
Message-ID: <60009@ti-csl.CSNET>
Date: 1 Oct 88 18:38:27 GMT
References: <2089@ssc-vax.UUCP> <441@kaon.uchicago.edu> <1401@devsys.oakhill.UUCP> <1851@loral.UUCP> <956@l.cc.purdue.edu>
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Reply-To: gateley@mips.UUCP (John Gateley)
Organization: TI Computer Science Center, Dallas
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In article <956@l.cc.purdue.edu> cik@l.cc.purdue.edu (Herman Rubin) writes:
>What is needed is something like
>#define fc(x,y) (LOCAL tmp1,tmp2; tmp1=x; tmp2=y; fc(x,y)=tmp1*tmp1+tmp2*tmp2)
>which should be interpreted correctly even if x or y happens to be tmp1 or tmp2.
>I do not know to what extent compiler implementations do this, but I doubt
>that a #define is treated other than a macro expansion, and I do not see
>how the problem can be avoided without something like this.

The ONLY place I have heard of this being done for macros is in the
programming language Scheme: using Eugene Kohlbecker's et al. beta-expansion
macro expander, or more recently Johnathon Rees's syntactic closures. I think
you are out of luck with C. What might help is a generate symbol operation.
This should give you a brand new symbol each time it is called. You might
be able to fake it in C somehow.

John Gateley
gateley@mips.csc.ti.com