Re: [rules-dev] modify( expr ) {....}

On 07/04/2011 06:44, Wolfgang Laun wrote: Perhaps I'm naive, but I think that it should be able to "compile" this by a mere expansion: modify( getFact( var ) ) { setName("yoda"), setColor("blue") } becomes getFact( var ).setName("yoda" ); getFact( var ). setColor("blue" ); update( getFact( var ) ); And just warn agsinst side effects. getFact( var) was just a simplificiation. It can allow for any expression of any complexity, it could pull from DB.

It means for each and every setter we would have to evaluate the whole expression. Mark I've written lots of rules for various mini-apps lately, and I've never had any reason to use anything except bound variables in a modify anyway. As for MVEL: I don't trust a "language" that doesn't provide a definition of its syntax. The less it is used in Drools (without the user asking for it) the better, Sorry if this hurts any feelings, but this reasoning is backed up by CENELEC. Cheers Wolfgang On 7 April 2011 07:14, Mark Proctor <mproctor(a)codehaus.org&gt; wrote: > I'm at the stage where I cannot make this work in a robust way when > using the java dialect: > modify( getFact( var ) ) { setName("yoda") } > > The problem is we have to infer the type of the expression. If the > expression is complex using variables in methods, we get method > ambiguity if we don't know all variable types. Once we have the > expression type we rewrite this as: > Person obj = ( Person) getFact(var); > obj.setName( "yoda" ); > > Edson did this originally by using mvel to analyse the expression. The > problem is that if the expression uses any local variables, we don't > know what those are. So we need to analyse the entire consequence, we > started to do this with MVEL but we have reached one too many stumbling > blocks - most recent of those is MVEL does not understand java generics. > I've put in about 3 weeks trying to solve this with mvel, and now had to > stop. When MVEL adds generics we can hopefully resume this work again. > > For now i'm having to roll back to our current behaviour. The positive > news is that no one has reported issues with this. I'm guessing most > people use just the fact instance, not expressions, and if they use an > expression it's simple. So the brittleness is not showing up. > > Anyway the work around for now is to explicitley cast, that should > resolve the issue, if it comes up for anyone. I'm tempted to say that > expressions are only officially supported when used with casting. > Atleast until we can do robust type inference: > modify( (Person) getFact( var ) ) { setName("yoda") } > > Mark > > _______________________________________________ > rules-dev mailing list > rules-dev(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/rules-dev > _______________________________________________ rules-dev mailing listrules-dev@lists.jboss.orghttps://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