Package org.projog.core.predicate.builtin.compound

Class Call

java.lang.Object

org.projog.core.predicate.builtin.compound.Call

All Implemented Interfaces:

KnowledgeBaseConsumer, PredicateFactory

public final class Call
extends java.lang.Object
implements PredicateFactory, KnowledgeBaseConsumer

call(X) - calls the goal represented by a term.

The predicate call makes it possible to call goals that are determined at runtime rather than when a program is written. call(X) succeeds if the goal represented by the term X succeeds. call(X) fails if the goal represented by the term X fails. An attempt is made to retry the goal during backtracking.

Projog also supports overloaded versions of call for which subsequent arguments are appended to the argument list of the goal represented by the first argument.

Field Summary

Fields

Modifier and Type	Field	Description
private KnowledgeBase	knowledgeBase

Constructor Summary

Constructors

Constructor	Description
Call()

Method Summary

Modifier and Type	Method	Description
private Predicate	getPredicate(Term arg)
Predicate	getPredicate(Term[] args)	Returns a Predicate to be used in the evaluation of a goal.
boolean	isRetryable()	Should instances of this implementation be re-evaluated when backtracking?
void	setKnowledgeBase(KnowledgeBase knowledgeBase)	Provides a reference to a KnowledgeBase.

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.projog.core.predicate.PredicateFactory

isAlwaysCutOnBacktrack

Field Detail

knowledgeBase

private KnowledgeBase knowledgeBase

Constructor Detail

Call

public Call()

Method Detail

getPredicate

public Predicate getPredicate(Term[] args)

Description copied from interface: PredicateFactory

Returns a Predicate to be used in the evaluation of a goal.

Specified by:

getPredicate in interface PredicateFactory

Parameters:

args - the arguments to use in the evaluation of the goal

Returns:

Predicate to be used in the evaluation of the goal

See Also:

Predicate.evaluate()

getPredicate

private Predicate getPredicate(Term arg)

isRetryable

public boolean isRetryable()

Description copied from interface: PredicateFactory

Should instances of this implementation be re-evaluated when backtracking?

Some goals (e.g. X is 1) are only meant to be evaluated once (the statement is either true or false) while others (e.g. repeat(3)) are meant to be evaluated multiple times. For instances of Predicate that are designed to possibly have Predicate.evaluate() called on them multiple times for the same individual query this method should return true. For instances of Predicate that are designed to only be evaluated once per individual query this method should return false.

Specified by:

isRetryable in interface PredicateFactory

Returns:

true if an attempt should be made to re-evaluate instances of implementing classes when backtracking, false otherwise

setKnowledgeBase

public void setKnowledgeBase(KnowledgeBase knowledgeBase)

Description copied from interface: KnowledgeBaseConsumer

Provides a reference to a KnowledgeBase.

Specified by:

setKnowledgeBase in interface KnowledgeBaseConsumer