[m-rev.] for review: make get_functor handle existential types

[Zoltan Somogyi]

On 13-Dec-2004, Ralph Becket <rafe at cs.mu.OZ.AU> wrote:
> > library/list.m:
> > 	Add two general-purpose predicates, all_true and all_false,
> > 	for use in the other library modules.
> 
> Are these really that useful?

I think so.

> > +list__all_true(_P, []).
> > +list__all_true(P, [X | Xs]) :-
> > +	P(X),
> > +	list__all_true(P, Xs).
> > +
> > +list__all_false(_P, []).
> > +list__all_false(P, [X | Xs]) :-
> > +	not P(X),
> > +	list__all_false(P, Xs).
> 
> Is there any efficiency difference between the above and these?
> 
> 	all [X] ( member(X, Xs) => P(X) )
> and
> 	all [X] ( member(X, Xs) => not P(X) )

Yes. Backtracking is slower than iteration.

> Stylistically, I prefer the latter.

Questions of taste are not all that useful as subjects of discussion.

Zoltan.
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