🚀 go-pugleaf

I implemented the following meta-interpreter for iterative
deepening in Prolog:

/*1*/	prove(G,N) :- prove(G,N,0).

	prove(true,N,N).
	prove((G1,G2),N,M) :-
		prove(G1,N,N1),
		prove(G2,N1,M).
	prove(G,N,M) :-
		N>0,
		N1 is N-1,
		clause(G,Gs),
		prove(Gs,N1,M).

One can add cuts as first subgoals to get more speed. Just for
fun I replaced the integer arithmetic for computing the depth
by peano arithmetic using a successor function s(N). I only had
to change the last clause into:

/*2*/	...
	prove(G,s(N),M) :-
		clause(G,Gs).
		prove(Gs,N,M).

Surprisingly, version /*2*/ is about 25% faster than version /*1*/.
After that I found out that it takes more time on my Prolog to
do a comparison and a substraction than to unfiy with s(N).

As Richard O'Keefe says "Elegancy is not optional". Version /*2*/
is more readable, uses no built-ins but clause/2 and one can even
call prove(G,N) with N unbound to get the behaviour of a standard
meta-interpreter!

thom fruehwirth, vienna