[rules-users] No eval with backward chaining?

[Mark Proctor]

Can you submit a pull request against master, 6.x, with the test. Put it in BackwardChainingTest. We'll back port the test and fix to 5.x.

thanks

Mark
On 21 Jun 2013, at 16:00, Wolfgang Laun <wolfgang.laun at gmail.com> wrote:

> Trying to use eval in a query for backward chaining causes a runtime
> crash running Drools 5.5.0. Looks like a bug. The details:
> 
> Given some Integer objects as facts,
>  rule "find triple forward"
>  when
>     Integer( $a: intValue )
>     Integer( $b: intValue > $a )
>     Integer( $c: intValue > $b )
>     eval( $a*$a + $b*$b == $c*$c )
>  then
>     System.out.println( "fwd: " + $a + " " + $b + " " + $c );
>  end
> finds Pythagorean triples.
> 
> But
>  query isTriple( Integer $a, Integer $b, Integer $c )
>     Integer( intValue == $a )
>     Integer( intValue == $b && > $a )
>     Integer( intValue == $c && > $b )
>     eval( $a*$a + $b*$b == $c*$c )
>  end
> intended to be used in combination with
>  rule "find triple backward"
>  when
>     isTriple( $a, $b, $c; )
>  then
>     System.out.println( "bwd: " + $a + " " + $b + " " + $c );
>  end
> causes a nasty runtime error (although DRL compilation succeeds):
> Exception in thread "main" java.lang.NoSuchMethodError:
> pythagoras.Rule_isTriple_17ac16f7237046ee9562afce35dfe174.eval0(III)Z
> 	at pythagoras.Rule_isTriple_17ac16f7237046ee9562afce35dfe174Eval0InvokerGenerated.evaluate(Unknown
> Source)
> 	at pythagoras.Rule_isTriple_17ac16f7237046ee9562afce35dfe174Eval0Invoker.evaluate(Unknown
> Source)
> 	at org.drools.rule.EvalCondition.isAllowed(EvalCondition.java:114)
> 	at org.drools.reteoo.EvalConditionNode.assertLeftTuple(EvalConditionNode.java:176)
> 	at org.drools.reteoo.SingleLeftTupleSinkAdapter.doPropagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:196)
> 	at org.drools.reteoo.SingleLeftTupleSinkAdapter.propagateAssertLeftTuple(SingleLeftTupleSinkAdapter.java:71)
> 	at org.drools.reteoo.JoinNode.propagateFromRight(JoinNode.java:159)
> 	at org.drools.reteoo.JoinNode.assertObject(JoinNode.java:148)
> 	at org.drools.reteoo.CompositeObjectSinkAdapter.doPropagateAssertObject(CompositeObjectSinkAdapter.java:497)
> 	at org.drools.reteoo.CompositeObjectSinkAdapter.propagateAssertObject(CompositeObjectSinkAdapter.java:382)
> 	at org.drools.reteoo.ObjectTypeNode.assertObject(ObjectTypeNode.java:235)
> 	at org.drools.reteoo.EntryPointNode.assertObject(EntryPointNode.java:240)
> 	at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:350)
> 	at org.drools.common.NamedEntryPoint.insert(NamedEntryPoint.java:311)
> 	at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:903)
> 	at org.drools.common.AbstractWorkingMemory.insert(AbstractWorkingMemory.java:847)
> 	at org.drools.impl.StatefulKnowledgeSessionImpl.insert(StatefulKnowledgeSessionImpl.java:269)
> 	at pythagoras.Main.makeFacts(Main.java:94)
> 	at pythagoras.Main.execute(Main.java:78)
> 	at pythagoras.Main.main(Main.java:103)
> 
> -W
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