Related to the modify expression, I 've always wondered about this code: rule "MyRule"   when     $p : Person(name = "Yoda")   then     modify ($p) {       setAge(300)     } end Doesn't this create an infinite loop? (In my experience it does or at least it takes a lot longer) Because the modify ($p) schedules any rule using a Person back on the agenda to be re-evaluated, so also that rule, which is evaluated and executed again, modifying $p again, ... hence the infinite loop? -- With kind regards, Geoffrey De Smet _______________________________________________ rules-dev mailing list rules-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-dev

Yes, It creates the exact same infinite loop that this code does: rule "MyRule" when $p : Person(name = "Yoda") then $p.setAge(300); update($p); end As far as I know, the results are the same. The modify() is a more compact way to do a lot of set() invocations and an update(). Maybe there are also some other advantages of using modify(), like optimization for example. Best Regards, XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX Esteban Aliverti - Developer @ http://www.plugtree.com - Blog @ http://ilesteban.wordpress.com On Fri, Apr 8, 2011 at 8:39 AM, Geoffrey De Smet <ge0ffrey.spam(a)gmail.com&gt;wrote: > Related to the modify expression, > I 've always wondered about this code: > > rule "MyRule" > when > $p : Person(name = "Yoda") > then > modify ($p) { > setAge(300) > } > end > > Doesn't this create an infinite loop? (In my experience it does or at > least it takes a lot longer) > Because the modify ($p) schedules any rule using a Person back on the > agenda to be re-evaluated, > so also that rule, which is evaluated and executed again, modifying $p > again, ... hence the infinite loop? > > -- > With kind regards, > Geoffrey De Smet > > > _______________________________________________ > rules-dev mailing list > rules-dev(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/rules-dev > _______________________________________________ rules-dev mailing list rules-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-dev

> Wouldn't it be great(?) and an optimisation that with "true modify" > (i.e. no longer a remove and insert) that we could only re-evaluate > rules that contained a pattern on a constraint affected by the update? I doubt if that is possible, consider this case with a calculated getter: class Person { private int age; public int getAgeInHours() { return 24 * age; } // getter and setter for int age } and these rules: rule "MyRule1" when $p : Person(name = "Yoda") then modify ($p) { setAge(300); } end rule "MyRule2" when $p : Person(ageInHours > 2400) then System.out.println("This guy is older than 2400 hours!"); end After MyRule1 fires and Yoda's age becomes 300, MyRule2 should fire because Yoda's older than 2400 hours. Next, add eval()'s in the mix for more cases like this. Op 08-04-11 14:11, Michael Anstis schreef: > Wouldn't it be great(?) and an optimisation that with "true modify" > (i.e. no longer a remove and insert) that we could only re-evaluate > rules that contained a pattern on a constraint affected by the update? > > So, > > rule "MyRule" > when > $p : Person(name = "Yoda") > then > modify ($p) { > setAge(300); > } > end > > would not cause "MyRule" to re-evaluate as there's enough information > present to ascertain that the modify does not alter the match. > > Tell me Wolfgang, why this is such a bad idea - I just know you'll > have a good explanation :) > > Cheers, > > Mike > > On 8 April 2011 13:00, Esteban Aliverti <esteban.aliverti(a)gmail.com > <mailto:esteban.aliverti@gmail.com>> wrote: > > Yes, It creates the exact same infinite loop that this code does: > > rule "MyRule" > when > $p : Person(name = "Yoda") > then > $p.setAge(300); > update($p); > end > > As far as I know, the results are the same. The modify() is a more > compact way to do a lot of set() invocations and an update(). > Maybe there are also some other advantages of using modify(), > like optimization for example. > > Best Regards, > > XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX > > Esteban Aliverti > - Developer @ http://www.plugtree.com <http://www.plugtree.com> > - Blog @ http://ilesteban.wordpress.com > > > > On Fri, Apr 8, 2011 at 8:39 AM, Geoffrey De Smet > <ge0ffrey.spam(a)gmail.com <mailto:ge0ffrey.spam@gmail.com>> wrote: > > Related to the modify expression, > I 've always wondered about this code: > > rule "MyRule" > when > $p : Person(name = "Yoda") > then > modify ($p) { > setAge(300) > } > end > > Doesn't this create an infinite loop? (In my experience it > does or at > least it takes a lot longer) > Because the modify ($p) schedules any rule using a Person back > on the > agenda to be re-evaluated, > so also that rule, which is evaluated and executed again, > modifying $p > again, ... hence the infinite loop? > > -- > With kind regards, > Geoffrey De Smet > > > _______________________________________________ > rules-dev mailing list > rules-dev(a)lists.jboss.org <mailto:rules-dev@lists.jboss.org> > https://lists.jboss.org/mailman/listinfo/rules-dev > > > > _______________________________________________ > rules-dev mailing list > rules-dev(a)lists.jboss.org <mailto:rules-dev@lists.jboss.org> > https://lists.jboss.org/mailman/listinfo/rules-dev > > > > _______________________________________________ > rules-dev mailing list > rules-dev(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/rules-dev -- With kind regards, Geoffrey De Smet _______________________________________________ rules-dev mailing list rules-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-dev

On 08/04/2011 12:39, Geoffrey De Smet wrote: > Related to the modify expression, > I 've always wondered about this code: > > rule "MyRule" > when > $p : Person(name = "Yoda") > then > modify ($p) { > setAge(300) > } > end > > Doesn't this create an infinite loop? (In my experience it does or at > least it takes a lot longer) > Because the modify ($p) schedules any rule using a Person back on the > agenda to be re-evaluated, > so also that rule, which is evaluated and executed again, modifying $p > again, ... hence the infinite loop? It would, unless you have slot specific - which Jess does. Slot specific is something I really want to add, I think it will resolve a lot of recursion problems and make Drools a lot easier to use. I took the slot specific problem and genericsed it further for "slot listeners". I discussed this here: http://blog.athico.com/2010/07/slot-specific-and-refraction.html. I think Laune added some refinements to this in a mailing list entry somewhere. Mark _______________________________________________ rules-dev mailing list rules-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-dev

OK, answers my question :)

It is on the "to do" list already. On 8 April 2011 13:11, Mark Proctor <mproctor(a)codehaus.org <mailto:mproctor@codehaus.org>> wrote: On 08/04/2011 12:39, Geoffrey De Smet wrote: > Related to the modify expression, > I 've always wondered about this code: > > rule "MyRule" > when > $p : Person(name = "Yoda") > then > modify ($p) { > setAge(300) > } > end > > Doesn't this create an infinite loop? (In my experience it does or at > least it takes a lot longer) > Because the modify ($p) schedules any rule using a Person back on the > agenda to be re-evaluated, > so also that rule, which is evaluated and executed again, modifying $p > again, ... hence the infinite loop? It would, unless you have slot specific - which Jess does. Slot specific is something I really want to add, I think it will resolve a lot of recursion problems and make Drools a lot easier to use. I took the slot specific problem and genericsed it further for "slot listeners". I discussed this here: http://blog.athico.com/2010/07/slot-specific-and-refraction.html. I think Laune added some refinements to this in a mailing list entry somewhere. Mark _______________________________________________ rules-dev mailing list rules-dev(a)lists.jboss.org <mailto:rules-dev@lists.jboss.org> https://lists.jboss.org/mailman/listinfo/rules-dev _______________________________________________ rules-dev mailing list rules-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-dev