Re: [9fans] multiple inputs

[Noah Evans <noah.evans@cwru.edu>]

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I think the idea of the hygenic macro is to implement the macro facility in to the compiler as a change to the parse tree rather than a change to the program text with a preprocessor(sorry if I'm being painfully obvious here).

This means that your macros don't have the normal problems associated with macros(precedence problems, multiple evaluation of arguments etc.). I haven't put very much thought into this, but from I'm guessing an implementation would act like a simplified yacc that worked with the compiler directly.

Again I'm not sure how practical this would be. The only implementation I know of, in scheme, is aided by scheme's use of prefix notation. Figuring out the precedence order would be a pain.

Thoughts?

Noah

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From: rog@vitanuova.com
To: 9fans@cse.psu.edu
Subject: Re: [9fans] multiple inputs
Date: Thu, 01 Apr 2004 18:36:36 +0100
Message-ID: <8cdad86de9428072d82f8764a903f798@vitanuova.com>

> which is much clearer and doesn't require us to wade through
> custom macro syntax.

i sympathise completely.

problem is the moment you have something that's flexible enough
to allow alt, you'll get someone that wants to do all kinds of other
things with it. remember:

LOCAL TREPTR	list(flg)
{
	REG TREPTR	r;
	REG INT		b;

	r = term(flg);
	WHILE r ANDF ((b=(wdval==ANDFSYM)) ORF wdval==ORFSYM)
	DO	r = makelist((b ? TAND : TORF), r, term(NLFLG));
	OD
	return(r);
}

what you're after, i think, is a different language, one with one or
two extra features, not really a way to customise C in an arbitrary
way.  a pre-processor could do the job, but you'd pay the price.

if many people defined syntax like the alt stuff, you'd really struggle
to work out what was going on. IMHO a language requires a small,
coherently designed set of features, not a way to add every feature
under the sun.