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Re: question on assert and retract--ground testing.

From: spratt
Subject: Re: question on assert and retract--ground testing.
Date: Tue, 27 Aug 2002 15:32:43 -0500

You piqued my interest, so I went to my benchmark source and looked at the 'ground' implementations. The implementation you provided is very near what appears to be the fastest implementation among the four I have.

Years ago (on Fri Feb 28 00:33:49 1992, to be precise), Richard A. O'Keefe posted an extensive note on 'ground' checking in the comp.lang.prolog newsgroup (as part of a discussion with David Bowen and Saumy K. Debray). I adopted RAOK's various forms of definition of ground as part of my 'benchmark' program.

Of these various forms (there are four, using univ and functor/arg in different ways), the fastest one for gprolog 1.2.13 on my G4 Mac is currently:

ground(Term) :-
        (   atomic(Term) -> true
        ;   nonvar(Term),
            Term =.. [_|Args],

ground_args([H|T]) :-

This one is two to three times faster than the functor/arg-based ground/1 programs. Go figure. (I'd expect functor/arg to be faster than univ.) As RAOK points out, it's important to measure actual performance, not just speculate. In the case of various ground/1 implementations, RAOK found that different implementations were the fastest on different systems.

This one differs from David's is_ground/1 in that:
is_ground/1 uses multiple clauses to test atom, number, and var, instead of a single clause using the builtin if-then-else in ground/1. There are no uses of cut in ground/1 or ground_args/1, and particularly is_ground_list/1 seems to have a spurious final clause and thus needless uses of cut .


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