Thank you Edson,

I am not a developer of drools, so I appreciate your sharing of design decisions here.

I still wish the “field constraint” be a field constraint no matter how this field is referenced, be it by name or by variable that references this field, otherwise it is more like “field name constraint”

So I wish I could do:

Person(

            $a : age,

            $minAge : 30,

            $maxAge : 40,

$a > $minAge && < $maxAge)

The introduction of local variable can be helpful when field names are complex and long (that is the case I have now), and need to be used more then once inside of expression. Also using eval involves performance penalty, so I would like to avoid it wherever possible,

Just my 2 cents…

-Sergey

---

From: rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of Edson Tirelli
Sent: Friday, August 10, 2007 3:17 PM
To: Rules Users List
Subject: Re: [rules-users] bug or feature not yet implemented

   Sergey,

   Well, a "field constraint" must always involve a field. The decision to have it on the left side is to simplify syntax. For instance, if you want to write something like: "age between 30 and 40", you can do:

Person( age > 30 && < 40 )

    So you declare the field only once and can have as many expressions applied over it as you want, using restriction connectives (&& and ||).

    Now, if your expression does not involve a field, then it is not a "field constraint". It may be an "inline-eval" (previously called predicate expression) for instance. And in this case, you use the "eval" keyword as showed in my previous example.
    Unfortunatelly, to avoid language ambiguities, we can't support arbitrary expressions without a markup keyword, and "eval" was the chosen keyword.

    []s
    Edson

2007/8/10, Manukyan, Sergey <SManukyan@lear.com>:

Thanks Edson for workaround,

IMHO that looks like a limitation to me, is there a particular reason why left side should always be a field?

-Sergey

---

From: rules-users-bounces@lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of Edson Tirelli
Sent: Friday, August 10, 2007 11:58 AM
To: Rules Users List
Subject: Re: [rules-users] bug or feature not yet implemented

   Sergey,

   That is how it is supposed to work. A field constraint in Drools always has a field at its left side. If you want arbitrary expression, just embed it in an inline eval:

        S : Supplier(
                $sts  : supplierBusinessStatus.businessStatus,
                $csts : corporateSupplier.supplierBusinessStatus.businessStatus,               
                eval ( $sts != $csts ) 
        )

   Although, for this specific case, it would be better (more performatic) to simply write:

        S : Supplier(
                $sts  : supplierBusinessStatus.businessStatus,
                $csts : corporateSupplier.supplierBusinessStatus.businessStatus != $sts
        )

    []s
    Edson

2007/8/10, Manukyan, Sergey <SManukyan@lear.com >:

Folks,

I found that drools 4.0GA doesn't recognize variables in the left side
of operator expression

Like this produces error:


When
        S : Supplier(
                $sts  : supplierBusinessStatus.businessStatus ,
                $csts :
corporateSupplier.supplierBusinessStatus.businessStatus,
                $sts != $csts
                )
Then
        ...



It tries to treat the $sts variable as a field of Supplier, instead
understanding that it is a variable declared earlier,

Please advise,

Thanks,

-Sergey




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--
  Edson Tirelli
  Software Engineer - JBoss Rules Core Developer
  Office: +55 11 3529-6000
  Mobile: +55 11 9287-5646
  JBoss, a division of Red Hat @ www.jboss.com

_______________________________________________
rules-users mailing list
rules-users@lists.jboss.org
https://lists.jboss.org/mailman/listinfo/rules-users

--
  Edson Tirelli
  Software Engineer - JBoss Rules Core Developer
  Office: +55 11 3529-6000
  Mobile: +55 11 9287-5646
  JBoss, a division of Red Hat @ www.jboss.com