🚀 go-pugleaf

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)