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From: jimv@omepd.UUCP
Newsgroups: comp.lang.c
Subject: Re: C & fp (really parens)
Message-ID: <549@omepd>
Date: Fri, 10-Apr-87 00:46:43 EST
Article-I.D.: omepd.549
Posted: Fri Apr 10 00:46:43 1987
Date-Received: Sat, 11-Apr-87 14:30:17 EST
References: <6800@brl-adm.ARPA>
Reply-To: jimv@omepd.UUCP (Jim Valerio)
Organization: Intel Corp., Hillsboro
Lines: 31
Summary: some improvements are no improvement at all

In article <6800@brl-adm.ARPA> dsill@NSWC-OAS.arpa writes:
>Given that a means for forcing the compiler to respect parentheses is needed,
>couldn't something less syntactically "tacky" than the unary + have been found?
>I don't think it's intuitive or obvious.  Someone, I don't remember who,
>suggested a "respect" reserved word to be used as:
>	respect x = expression...;
>which wouldn't be too bad.

I'm sorry, but "respect ..." doesn't seem like an improvement over the
unary + syntax to me.  (There's a Rodney Dangerfield joke in here
somewhere.)

An alternate approach is to write a preprocessor to run over the C code
that enforces parentheses by rewriting those expressions as individual
statements to guarantee the order of evaluation.  I grant that some
rewrites are tricky to do since expressions and statements don't always
mix well in C, but this approach does enforce the order of evaluation.

One gotcha might be that, to get reasonable code generated, the
rewriting could require declaring extended-width floating-point data
types (such as long double) which may or may not be supported in any
particular compiler.  I'm thinking here of those floating-point chips
that prefer to keep intermediate expressions in an extended-width
format.

I consider the rewriting approach to be somewhat similar to the inline
function preprocessor I've been using here.  Source level rewriting is
useful, and can be done separately from the compiler, but it is easier
to directly implement the desired semantics in the compiler proper.
--
Jim Valerio	{verdix,intelca!mipos3}!omepd!jimv, jimv@omepd.intel.com