Re: JESS: No-loop issue

> Hi Dr. Friedman-Hill,
>
> I ran into a bug in my rulebase today that I traced back to the use of
> the no-loop declaration (test case below).  This has bit other users  
> in
> the past (see urls below), and I think it should be regarded as a bug.
>
> In my example, two separate facts (f-2 and f-3) activate a no-loop
> rule.  When the rule fires for f-3, it modifies (retracts and  
> reasserts)
> another fact, causing the activation associated with f-2 to be  
> removed.
> However, when the fact is reasserted, 'no-loop' prevents the engine  
> from
> restoring the activation for f-2.
>
> This behavior seems inconsistent with the definition of the no-loop
> declaration.  The RHS of a 'no-loop' rule must not *cause* the  
> immediate
> reactivation of the same rule, but it should not inhibit an activation
> that was already present when the rule fired.
>
> Thanks,
> ~~Aaron Novstrup
>
> http://www.mail-archive.com/jess-users@.../msg08025.html
> http://www.mail-archive.com/jess-users@.../msg09870.html
>
> ; JESS test case
> (deftemplate box
>   (multislot items))
>
> (deffunction put-in-box (?box ?item)
>   (bind ?items (fact-slot-value ?box items))
>   (modify ?box (items (union$ ?items (create$ ?item))))
>   )
>
> (defrule box-packer-rule
>   (declare (no-loop TRUE))
>   (moving ?item)
>   ?b <- (box)
>   =>
>   (put-in-box ?b ?item)
>   )
>
> (watch all)
> (reset)
>
> (assert (box))
> (assert (moving elvis-bobble-head-collection))
> (assert (moving jimi-hendrix-autographed-guitar))
> (run)
>
> ; execution trace
> Jess, the Rule Engine for the Java Platform
> Copyright (C) 2008 Sandia Corporation
> Jess Version 7.1p2 11/5/2008
>
> ==> Focus MAIN
> ==> f-0 (MAIN::initial-fact)
> ==> f-1 (MAIN::box (items ))
> ==> f-2 (MAIN::moving elvis-bobble-head-collection)
> ==> Activation: MAIN::box-packer-rule :  f-2, f-1
> ==> f-3 (MAIN::moving jimi-hendrix-autographed-guitar)
> ==> Activation: MAIN::box-packer-rule :  f-3, f-1
> FIRE 1 MAIN::box-packer-rule f-3, f-1
> <== Activation: MAIN::box-packer-rule :  f-2, f-1
> <=> f-1 (MAIN::box (items jimi-hendrix-autographed-guitar))
> <== Focus MAIN
>
> <anovstrup.vcf>