Once

java.lang.Object
- org.projog.core.predicate.AbstractSingleResultPredicate
- - org.projog.core.predicate.builtin.compound.Once

All Implemented Interfaces:

KnowledgeBaseConsumer, PredicateFactory, PreprocessablePredicateFactory
```
public final class Once
extends AbstractSingleResultPredicate
implements PreprocessablePredicateFactory
```
once(X) - calls the goal represented by a term.
The once(X) goal succeeds if an attempt to satisfy the goal represented by the term X succeeds. No attempt is made to retry the goal during backtracking - it is only evaluated once.

- Nested Class Summary
  
  Nested Classes
  Modifier and Type Class Description
  
  private static class Once.OptimisedOnce
- Constructor Summary
  
  Constructors
  Constructor Description
  
  Once()
- Method Summary
  
  All Methods Instance Methods Concrete Methods
  Modifier and Type Method Description
  
  protected boolean evaluate(Term t)
  
  PredicateFactory preprocess(Term term)
  - Methods inherited from class org.projog.core.predicate.AbstractSingleResultPredicate
    evaluate, evaluate, evaluate, evaluate, evaluate, getArithmeticOperators, getFileHandles, getKnowledgeBase, getOperands, getPredicate, getPredicates, getProjogListeners, getSpyPoints, getTermFormatter, init, isRetryable, setKnowledgeBase
  - Methods inherited from class java.lang.Object
    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
  - Methods inherited from interface org.projog.core.predicate.PredicateFactory
    getPredicate, isAlwaysCutOnBacktrack, isRetryable

- Constructor Detail
  - Once
```
public Once()
```
- Method Detail
  - evaluate
```
protected boolean evaluate(Term t)
```
    Overrides:
    
    evaluate in class AbstractSingleResultPredicate
  - preprocess
```
public PredicateFactory preprocess(Term term)
```
    Specified by:
    
    preprocess in interface PreprocessablePredicateFactory