org.projog.core.predicate

Interface Predicate

All Known Implementing Classes:

InterpretedUserDefinedPredicate, SucceedsNeverPredicate, SucceedsOncePredicate, TailRecursivePredicate

public interface Predicate

Represents a goal.

See Also:

PredicateFactory, Predicates.addPredicateFactory(PredicateKey, String)

Method Summary

Modifier and Type	Method and Description
boolean	couldReevaluationSucceed() Could the next re-evaluation of this instance succeed?
boolean	evaluate() Attempts to satisfy the goal this instance represents.

Method Detail

evaluate

boolean evaluate()

Attempts to satisfy the goal this instance represents.

Calling this method multiple times on a single instance allows all possible answers to be identified. An attempt to find a solution carries on from where the last successful call finished.

If PredicateFactory.isRetryable() returns false then this method should only be called once per individual query (no attempt should be made to find alternative solutions).

If PredicateFactory.isRetryable() returns true then, in order to find all possible solutions for an individual query, this method should be recalled on backtracking until it returns false.

Returns:

true if it was possible to satisfy the clause, false otherwise

See Also:

PredicateFactory.getPredicate(Term[])

couldReevaluationSucceed

boolean couldReevaluationSucceed()

Could the next re-evaluation of this instance succeed?

Specifies whether a specific instance of a specific implementation of Predicate, that has already had evaluate() called on it at least once, could possibly return true the next time evaluate() is called on it. i.e. is it worth trying to continue to find solutions for the specific query this particular instance represents and has been evaluating?

(Note: the difference between this method and PredicateFactory.isRetryable() is that PredicateFactory.isRetryable() deals with whether, in general, a specific implementation (rather than instance) of Predicate could ever produce multiple answers for an individual query.)

Returns:

true if an attempt to re-evaluate this instance could possible succeed, false otherwise