org.projog.core.predicate.udp

Class TailRecursivePredicateMetaData

java.lang.Object

org.projog.core.predicate.udp.TailRecursivePredicateMetaData

public final class TailRecursivePredicateMetaData
extends Object

Defines the characteristics of a tail recursive user defined predicate.

Projog uses the following rules to determine if a user defined predicate is "tail recursive" (and therefore suitable for tail recursion optimisation using a TailRecursivePredicate):

• The user defined predicate must consist of exactly 2 rules.
• It must be possible to detect, at the point that the user defined predicate is defined, that the antecedent of the first rule will never generate multiple solutions per-query.
• If the antecedent of the second rule is not a conjunction, it must be a call to itself (i.e. the user defined predicate being defined) - this is what makes the predicate recursive.
• If the antecedent of the second rule is a conjunction, the final element (i.e. the tail) of the conjunction must be a call to itself (i.e. the user defined predicate being defined) - this is what makes the predicate recursive. It must be possible to detect, at the point that the user defined predicate is defined, that all elements prior to the final element of the conjunction will never generate multiple solutions per-query.

Examples of tail recursive predicates suitable for tail recursion optimisation:

 :- list([]).
 list([X|Xs]) :- list(Xs).
 

 r(N).
 r(N) :- N > 1, N1 is N-1, r(N1).
 

 writeAndRepeat(N) :- write(N), nl.
 writeAndRepeat(N) :- N > 1, N1 is N-1, writeAndRepeat(N1).
 

See Also:

TailRecursivePredicate

Method Summary

Modifier and Type	Method and Description
static TailRecursivePredicateMetaData	create(KnowledgeBase kb, List<ClauseModel> clauses) Returns a new TailRecursivePredicateMetaData representing the user defined predicate defined by the specified clauses or null if the predicate is not tail recursive.
ClauseModel	getFirstClause()
ClauseModel	getSecondClause()
boolean	isPotentialSingleResult()
boolean	isSingleResultIfArgumentImmutable(int idx)
boolean	isTailRecursiveArgument(int idx)

Methods inherited from class java.lang.Object

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

Method Detail

create

public static TailRecursivePredicateMetaData create(KnowledgeBase kb,
                                                    List<ClauseModel> clauses)

Returns a new TailRecursivePredicateMetaData representing the user defined predicate defined by the specified clauses or null if the predicate is not tail recursive.

Parameters:

clauses - the clauses that the user defined predicate consists of

Returns:

a new TailRecursivePredicateMetaData or null if the predicate is not tail recursive

getFirstClause

public ClauseModel getFirstClause()

getSecondClause

public ClauseModel getSecondClause()

isPotentialSingleResult

public boolean isPotentialSingleResult()

isTailRecursiveArgument

public boolean isTailRecursiveArgument(int idx)

isSingleResultIfArgumentImmutable

public boolean isSingleResultIfArgumentImmutable(int idx)