Package org.projog.core.predicate.builtin.list

Class Fold.Retryable

java.lang.Object

org.projog.core.predicate.builtin.list.Fold.Retryable

All Implemented Interfaces:

Predicate

Enclosing class:

Fold

private static class Fold.Retryable
extends java.lang.Object
implements Predicate

Field Summary

Fields

Modifier and Type	Field	Description
private java.util.List<Variable>	accumulators
private Term	action
private java.util.List<Term>	backtrack1
private java.util.List<Term>	backtrack2
private int	idx
private PredicateFactory	pf
private java.util.List<Predicate>	predicates
private Term	result
private Term	start
private java.util.List<Term>	values

Constructor Summary

Constructors

Modifier	Constructor	Description
private	Retryable(PredicateFactory pf, Term action, java.util.List<Term> values, Term start, Term result)

Method Summary

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

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

pf

private final PredicateFactory pf

action

private final Term action

values

private final java.util.List<Term> values

start

private final Term start

result

private final Term result

predicates

private final java.util.List<Predicate> predicates

accumulators

private final java.util.List<Variable> accumulators

backtrack1

private final java.util.List<Term> backtrack1

backtrack2

private final java.util.List<Term> backtrack2

idx

private int idx

Constructor Detail

Retryable

private Retryable(PredicateFactory pf,
                  Term action,
                  java.util.List<Term> values,
                  Term start,
                  Term result)

Method Detail

evaluate

public boolean evaluate()

Description copied from interface: Predicate

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.

Specified by:

evaluate in interface Predicate

Returns:

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

See Also:

PredicateFactory.getPredicate(Term[])

couldReevaluationSucceed

public boolean couldReevaluationSucceed()

Description copied from interface: Predicate

Could the next re-evaluation of this instance succeed?

Specifies whether a specific instance of a specific implementation of Predicate, that has already had Predicate.evaluate() called on it at least once, could possibly return true the next time Predicate.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.)

Specified by:

couldReevaluationSucceed in interface Predicate

Returns:

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