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prologswi-prolog

How to call a goal and bind the number of logical inferences to a variable in Prolog?

According to the manual, time(+Goal) executes Goal and prints, amongst other things, the number of logical inferences used.

How can I bind the number of logical inferences to a variable?

Solution

  • The following code is specific to SWI-Prolog. Currently, many other Prologs do not permit to count the number of inferences, mainly due to many different optimizations that would blur that number.

    :- meta_predicate(call_inferences(0, -)).

call_inferences(Goal_0, Inferences) :-
   statistics(inferences, I0),
   Goal_0,
   statistics(inferences, I1),
   Inferences is I1-I0-1.

    Usage:

    ?- call_inferences(true,N).
   N = 1.
?- call_inferences(nreverse([1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30],L), N).
   L = [30, 29, 28, 27, 26, 25, 24, 23, 22|...], N = 496.