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Grandparent <state> for <final>

From: Gavin Kistner <phrogz@mac.com>
Date: Wed, 28 Jun 2017 22:10:39 +0000 (GMT)
To: "www-voice@w3.org" <www-voice@w3.org>
Message-id: <0d31fb50-0f2c-4b7b-98c9-54cf3e175cfc@me.com>
A couple years ago I wrote a Lua interpreter for SCXML[1]. Stefan R. just filed a bug with it[2]. At the core of the issue is whether the following SCXML parallel should be 'in a final/done state' after being entered:

    <parallel id="p0">
        <state id="p0_s0">
            <state id="p0_s0_s0"><final id="p0_s0_s0_f0"/></state>
        </state>
        <state id="p0_s1">
            <state id="p0_s1_s0"><final id="p0_s1_s0_f0"/></state>
        </state>
    </parallel>

My interpreter fires "done.state.p0_s0_s0" and "done.state.p0_s1_s0". However, it does not cause "p0_s0" or "p0_s1" to be considered in a final state, and therefore does not consider the parallel to be in a final state.

On the one hand, this clearly looks like a bug in my interpreter against how I would *expect* the specifications to handle this situation. On the other hand, the specifications+errata only appear to cover situations where a <parallel> is exactly a *grandparent* of the <final>, not any further ancestor.

Section 3.7 of the spec says:

"When the state machine enters the <final> child of a <state> element […] generate the event done.state.id [...] where id is the id of the parent state. Immediately thereafter, if the parent <state> is a child of a <parallel> element, and all […] other children are also in final states […] generate the event done.state.id where id is the id of the <parallel> element."

This only covers exactly the parent of the <final>, not any grandparent <state> or great-grandparent <parallel>.

Further, the pseudo-code for Appendix D explicitly only handles one level at the end of enterStates(), and also only handles one level for the definition of isInFinalState().


If Stefan (and my) belief about how this should behave is correct, then (a) the prose in 3.7 needs to be modified via errata, and (b) the isInFinalState() pseudo-code should be modified to recurse, and (c) we need to discuss whether grandparent <state> also fire "done.state.xxx" events when their child state becomes in a final state, and if so, modify the pseudo-code in enterStates() to do so.

If we're wrong—if grandparent states do not get this event fired, are not considered in a final state, and if the parallel in the example above should also not be in a final state—I'd be very interested to hear some arguments for this.

[1] https://github.com/Phrogz/LXSC
[2] https://github.com/Phrogz/LXSC/issues/1

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Received on Wednesday, 28 June 2017 22:11:13 UTC

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