Class Call

java.lang.Object
org.projog.core.predicate.builtin.compound.Call
All Implemented Interfaces:
KnowledgeBaseConsumer, PredicateFactory
public final class Call extends 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.

  • Constructor Details

    • Call

      public Call()

  • Method Details

    • 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:

    • 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