[rules-users] No eval with backward chaining?

[Wolfgang Laun]

Below is a self-contained DRL file where Drools crashes during evaluation
at runtime, even though it compiles and appears to be correct.

package pythagoras;

rule "kickoff"
salience 100
when
then
    for( Integer i: new Integer[]{3,4,5,12,13 } ){
       insert( i );
    }
end

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

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

rule "find triple backward"
when
   isTriple( $a, $b, $c; )
then
   System.out.println( "bwd: " + $a + " " + $b + " " + $c );
end


On 21/06/2013, Mark Proctor <mproctor at codehaus.org> wrote:
> 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
>> _______________________________________________
>> rules-users mailing list
>> rules-users at lists.jboss.org
>> https://lists.jboss.org/mailman/listinfo/rules-users
>
>
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