Not getting into whether this is a bad practice, the only language I've ever seen support this syntax is COBOL. Every other language I've worked in (and there are many) do not support this technique, so it seems reasonable that this syntax should be disallowed in drools as well. ________________________________ From: rules-users-bounces(a)lists.jboss.org [mailto:rules-users-bounces@lists.jboss.org] On Behalf Of Edson Tirelli Sent: Monday, March 16, 2009 9:58 AM To: Rules Users List Subject: Re: [rules-users] single binding for or CE flagged by compiler This is an old discussion. Single binding on "or" is a non-orthogonal special case on the language syntax that was introduced in the early days when we only had "infix" CEs. When we started to support prefix CE, the special case was not updated, and as a result, the single binding works only with infix. IMO, this syntax promotes bad practices and should be disallowed. Although, some people like it and it is still in there. Just to clarify why I think it promotes bad practice: * When you have the same object type for all the patterns inside an "or" group, you should be using constraint connector ||, not the "or" CE. Using your example: $t : Trigger( fa == 1 || == 2 ) // or any variation of the syntax. This keeps the network smaller and prevents unexpected behavior when the constraints are not mutually exclusive and in some cases people forget that the rule will fire once for each logical branch when using "or". * If the object types are different, then you can't use single binding anyway: $o : ( Cheese() or Wine() ) // this will lead to ClassCastExceptions on the usage of $o. So, I really think that the "single binding or" fulfilled its purpose on Drools 3, when we didn't had all the flexibility in the language we have today. But now, the only thing it achieves is promoting bad practices. Just my 0.02c. []s Edson 2009/3/16 Wolfgang Laun <wolfgang.laun(a)gmail.com&gt; As far as I know, this should work: package orel; import orel.Main.Trigger; rule ror1 when $t : (or Trigger(fa == 1) Trigger(fa == 2)) then System.out.println( "fired " + $t.getName() ); end This is what Drools-5.0.0 kbuilder.getErrors().toString() returns: [5,11]: [ERR 102] Line 5:11 mismatched input 'Trigger' expecting '(' in rule ror1 in pattern or[6,14]: [ERR 102] Line 6:14 mismatched input 'Trigger' expecting ')' in rule ror1[6,30]: [ERR 102] Line 6:30 mismatched input ')' expecting 'then' in rule ror1 Shouldn't toString() insert line ends? As it is, the result is pretty much useless. This works: rule ror1 when (or $t : Trigger(fa == 1) $t : Trigger(fa == 2)) then System.out.println( "fired " + $t.getName() ); end -W _______________________________________________ rules-users mailing list rules-users(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-users -- Edson Tirelli JBoss Drools Core Development JBoss, a division of Red Hat @ www.jboss.com

Sorry, my focus was on the feature, so I was not clear. This is how the documentation should look overall. I will use [ ] to denote groups. Any pattern takes the form: <pattern_decl> ::= <variable> : <pattern> You can combine patterns using infix or prefix CEs "and" and "or" (both forms are equivalents). Example using "or": <pattern_decl> [ or <pattern_decl> ]* ( or <pattern_decl> [ <pattern_decl> ]* ) Now, there is this beast in the syntax that allow a special case of "or" that works only like this: <variable> : ( <pattern> [ or <pattern> ]* ) For the special case above, only infix "or" is accepted and the internal patterns don't accept bindings. I agree with you that a fix is needed: either we remove the syntax completely or we keep it for backward compatibility, but either way we need the documentation to be updated accordingly. I think the orthogonal form is less error prone because it is orthogonal and you would rarely use it when writing rules manually (binding to the same variable), and if you do, you are explicitly showing your intent. Anyway, discussion is still open, but the docs needs clarification, yes. []s Edson 2009/3/16 Wolfgang Laun <wolfgang.laun(a)gmail.com&gt; -- Edson Tirelli JBoss Drools Core Development JBoss, a division of Red Hat @ www.jboss.com