🚀 go-pugleaf

In article <1992Sep1.160505.6828@irisa.fr>, serge@irisa.fr (Serge Lehuitouze) writes:
> You, WAM gurus, do you do anything special about this construct, or do you just
> consider it as an ordinary predicate with a definition like:
> P ;_Q :- P.
> _P; Q :- Q.

There is a third possibility:  when a clause contains a goal of the form
(P ; Q), e.g. H :- A, (P ; Q), B
split that goal out as a separate predicate:
	T(Xs) :- P.
	T(Xs) :- Q.
	H :- A, T(Xs), B.
where Xs is vars([P,Q]) intersect vars([H,A,B]).

But yes, disjunction is usually compiled specially, for two important
reasons:
    1.  It would be unreasonably slow and inefficient to do otherwise.
    2.  Disjunction and if->then;else are transparent to cuts, that is,
	a cut inside one of them has effect on the whole predicate,
	not just the disjunction or if->then;else.

-- 
You can lie with statistics ... but not to a statistician.