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From: ok@goanna.cs.rmit.oz.au (Richard A. O'Keefe)
Newsgroups: comp.lang.prolog
Subject: Re: Prolog's Pitfalls?
Message-ID: <3449@goanna.cs.rmit.oz.au>
Date: 20 Jul 90 09:37:15 GMT
References: <1990Jun18.221058.11331@chaos.cs.brandeis.edu> <31467@cup.portal.com>
Organization: Comp Sci, RMIT, Melbourne, Australia
Lines: 27

In article <31467@cup.portal.com>, pgl@cup.portal.com (Peter G Ludemann) writes:
> There's another technique, which no-one seems to have mentioned:
> meta-grammar rules.  What you want here is a sequence of "prim"s:
> 
> 	expr(E) --> seq(prim,E) .
> 
> No problem: just define a meta-rule:
> 
> 	seq(X,[E1|E2]) --> X(E1), seq(X,E2) .
> 	seq(X,[])      --> [] .
> 
In current Quintus Prolog, use 'phrase':

	seq(X, [E1|E2]) --> {augment_term(X1, X, E1)}, phrase(X1),
			    seq(X, E2).
	seq(X, []) --> [].

I'll add phrase/N for N > 3 (i.e. phrase//M for M > 1) to the library
so that you'll be able to write

	seq(X, [E1|E2]) --> phrase(X, E1), seq(X, E2).

Generally speaking, where you would have used call/N in ordinary code
you would use phrase//N in a grammar rule.
-- 
Science is all about asking the right questions.  | ok@goanna.cs.rmit.oz.au
I'm afraid you just asked one of the wrong ones.  | (quote from Playfair)