7.10.3 Restraint answer count

Finally, using “as max_answers(Count)” or the Prolog flag max_answers_for_subgoal, the number of answers in a table is restrained. In addition to the tripwire actions this restraint supports the action bounded_rationality^{171The action complete_soundly is supported as a synonym for XSB compatibility}. If the restraint is reached in the bounded rationality mode the system takes the following actions:

• Ignore the answer that triggered the restraint.
• Prune the choice points of the tabled goal to avoid more answers.
• Add an new answer to the table that does not bind any variables, i.e., an empty answer substitution. This answer is conditional on answer_count_restraint/0.

[undefined]answer_count_restraint

This predicate is undefined in the sense of well founded semantics (see section 7.6 and undefined/0). Any answer that depends on this condition is undefined because the max_answers restraint on some table was violated.

The program and subsequent query below illustrate the behavior.

:- table p/2 as max_answers(3).

p(M,N) :-
    between(1,M,N).

?- p(1 000 000, X).
X = 3 ;
X = 2 ;
X = 1 ;
% WFS residual program
    p(1000000, X) :-
        answer_count_restraint.
p(1000000, X).