How to get data model info from interpreter

[crichardson332]

I'm trying to figure out how to pass data into my state machine from external events, and then extract that data using the uscxml interpreter. My scxml looks something like this:

<scxml name="Scxml" initial="State0" version="1.0" xmlns="http://www.w3.org/2005/07/scxml">
    <transition event="GoState1" target="State1"/>
    <state id="State1">
        <datamodel>
            <data id="Num"/>
        </datamodel>
        <onentry>
            <assign location="Num" expr="_event.data"/>
        </onentry>
    </state>
</scxml>

I'm able to assign data to Num when I push the event into the interpreter externally, but now I can't figure out how to see that data from the interpreter after performing a macrostep. Does the interpreter class have this, or am I approaching this wrong? I'm also still learning the scxml standard so I might not be setting up my scxml file correctly.

[alexzhornyak]

Your example contains the next errors: 1) NULL datamodel does not support location and value expressions 2) \<transition> element can not be child of \<scxml> element

Actually, your question was not fully clear, so, I made one simple example. May be it will help you.

<scxml datamodel="lua" name="Scxml" version="1.0" xmlns="http://www.w3.org/2005/07/scxml">
    <state id="State1">
        <datamodel>
            <data expr="5" id="Num"/>
        </datamodel>
        <transition target="FinalShape1"/>
    </state>
    <final id="FinalShape1">
        <onentry>
            <assign expr="Num + 5" location="Num"/>
        </onentry>
    </final>
</scxml>

Interpreter interpreter = Interpreter::fromURL("github_issue_189_1.scxml");

InterpreterState state = InterpreterState::USCXML_UNDEF;
while (state != InterpreterState::USCXML_FINISHED) {
    state = interpreter.step();
}

auto numData = interpreter.getImpl()->getAsData("Num"); // Not Evaluated
// auto numData = interpreter.getImpl()->evalAsData("Num"); // Evaluated
std::cout << std::stol(numData);

Output: 10

[crichardson332]

Thanks! I've got something working now.

I ran into another issue though when trying to run my application inside a docker container. On my host, all my tests run fine; but inside docker my code crashes with output that isn't useful. So I ran uscxml-browser -c on my scxml file and got the following output:

[Debug] Issue (FATAL) at /scxml[1]: SCXML document requires unknown datamodel 'ecmascript'

The same thing happens with lua as well:

[Debug] Issue (FATAL) at /scxml[1]: SCXML document requires unknown datamodel 'lua'

This docker container definitely doesn't have all the packages that a normal ubuntu desktop would have. What packages do I need to install for this to work?

Also, I noticed in your NullDataModel implementation that it uses the Data class's fromJSON() function to get data. All I really need from the data model is to store dictionaries in something like a JSON format...can I just use the null datamodel? The scxml documentation makes it sound like the null is meant for a non-existent data model, but if I can at least do JSON dictionaries then that works for me.

[crichardson332]

Never mind, I figured it out. Turns out, the docker container did not have the scripting languages installed, but I specified the language in my scxml file so it was crashing.

For ecmascript, you need to install a javascript engine, like so

sudo apt install libjavascriptcoregtk-4.0-dev

And similar packages if you're using lua, or any of the other scripting languages. But for ecmascript you only need the javascript one.