Class IfThen

java.lang.Object

org.projog.core.predicate.builtin.compound.IfThen

All Implemented Interfaces:

PredicateFactory

public final class IfThen
extends Object
implements PredicateFactory

X->Y - if X succeeds then Y is evaluated.

Note: The behaviour of this predicate changes when it is specified as the first argument of a structure of the form ;/2, i.e. the "disjunction" predicate. When a ->/2 predicate is the first argument of a ;/2 predicate then the resulting behaviour is a "if/then/else" statement of the form ((if->then);else).

See Also:

• Disjunction

Constructor Summary

Constructors

Constructor	Description
IfThen(KnowledgeBase kb)

Method Summary

Modifier and Type	Method	Description
Predicate	getPredicate(Term term)	Returns a Predicate to be used in the evaluation of a goal.
boolean	isRetryable()	Should instances of this implementation be re-evaluated when backtracking?
PredicateFactory	preprocess(Term term)

Methods inherited from class Object

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

Methods inherited from interface PredicateFactory

isAlwaysCutOnBacktrack

Constructor Details

IfThen

public IfThen(KnowledgeBase kb)

Method Details

preprocess

public PredicateFactory preprocess(Term term)

Specified by:

preprocess in interface PredicateFactory

getPredicate

public Predicate getPredicate(Term term)

Description copied from interface: PredicateFactory

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

Specified by:

getPredicate in interface PredicateFactory

Parameters:

term - the term containing 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()

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