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From "Rahul Akolkar" <rahul.akol...@gmail.com>
Subject Re: [SCXML] Implementation of system variables in a separate context?
Date Fri, 05 Dec 2008 21:28:22 GMT
On Fri, Dec 5, 2008 at 8:02 AM, Ingmar Kliche
<ingmar.kliche@googlemail.com> wrote:
> Rahul,
>
> the latest SCXML WD [1] describes a set of system variables which are
> read-only for the application. See section 5.5 [2]: "The Data Module
> maintains a protected portion of the data model containing information that
> may be useful to applications...."
>
> This could be implemented in commons-scxml using an additional context and
> set it as the parent of the current root context. Some expression languages
> (such as ECMAScript) support scope chains and allow to attach scopes read
> only.
<snip/>

We may need to abstract out the notion of a partitioned root context,
just like we have a notion of ordinary context.


> Other expression languages may require a special treatment of this
> "system variable context". In this case it could be necessary to implement a
> special context which handles the read-only behavior.
>
<snap/>

Yes, its read-only in a limited sense (for the application developer
i.e. within the SCXML document -- not for the implementation i.e.
_event for example keeps changing with each event so the executor
needs to be able to write to it).


> At the same time we could change the "eventname" and "eventvalue" variables
> to "_event.name" and "_event.value".
>
<snip/>

Yeah, that needs to be done (though I think you mean "_eventdata"
instead of "eventvalue").

If you feel like it, do open a JIRA issue to track this for the next release.

-Rahul



> What do you think?
>
> - Ingmar.
>
> [1] http://www.w3.org/TR/2008/WD-scxml-20080516/
> [2] http://www.w3.org/TR/2008/WD-scxml-20080516/#SystemVariables
>

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