[news.eclipse.modeling.mdt.ocl] Re: def expression?

[Joel Greenyer <jgreen@xxxxxx>]

Ed,
I've been trying to get familiar with nested environments, You promised that they were easy to use ;), but unfortunately 
I can't find code examples--at least not any that point in the direction that I need to go.

In short, my problem is that I match a graph pattern to a model and, during the matching process, I need a scope that 
constantly reflects the bound nodes by bound variables, i.e. the scope must contain a bound variable per named node that 
is currently bound.

While I backtrack, I need to remove variables from my environment/scope that will possibly be added again. So, you 
suggest to do this with nested environments--How do I create a nested environment (I think I understood that...) and how 
to I go back to an outer environment when I backtrack?

Thanks for helping!

Joel


Ed Willink wrote:
> Hi Joel
> > > I'm not sure about your whole problem but when you mention removing 
> > > variables from environments I get very uncomfortable. 
> >
> > Why is that?
>
> It means that the Environment has a very clear locality. Nested 
> environments are always valid for the context that initialised them.
>
> Note that OCL 2.0 does not support remove of elements from an Environment.
> > > It is much easier
> > > to created a nested environment for the nested scope and revert to the
> > > outer ebvironment when you want to recover context.
>
> You'll find nested environments are easy too, and you cannot forget to 
> match your adds with removes.
> > I haven't worked with these nested environments yet, but I'll keep it 
> > in mind. However, I'd have to create a nested environment for each 
> > variable that I add. Adding and removing variables is easy and works 
> > well for me so far.
>
> If it works for you fine. Just beware that if you start to do more 
> interesting things, it might bite later.
>
>     Regards
>
>         Ed Willink