Class Length

java.lang.Object
org.projog.core.predicate.builtin.list.Length
All Implemented Interfaces:
PredicateFactory
public final class Length extends Object implements PredicateFactory
length(X,Y) - determines the length of a list.

The length(X,Y) goal succeeds if the number of elements in the list X matches the integer value Y.

  • Constructor Details

    • Length

      public Length()

  • Method Details

    • 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:

    • 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