Class Nth

java.lang.Object

org.projog.core.predicate.builtin.list.Nth

All Implemented Interfaces:

PredicateFactory

public final class Nth
extends Object
implements PredicateFactory

nth0(X,Y,Z) / nth1(X,Y,Z) - examines an element of a list.

Indexing starts at 0 when using nth0. Indexing starts at 1 when using nth1.

Method Summary

Modifier and Type	Method	Description
Predicate	getPredicate(Term input)	Returns a Predicate to be used in the evaluation of a goal.
boolean	isRetryable()	Should instances of this implementation be re-evaluated when backtracking?
static Nth	nth0()
static Nth	nth1()

Methods inherited from class Object

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

Methods inherited from interface PredicateFactory

isAlwaysCutOnBacktrack, preprocess

Method Details

nth0

public static Nth nth0()

nth1

public static Nth nth1()

getPredicate

public Predicate getPredicate(Term input)

Description copied from interface: PredicateFactory

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

Specified by:

getPredicate in interface PredicateFactory

Parameters:

input - 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