PlantUML: add arrow from history to initial memory

[Zinoex]

In the style of David Harels paper Statecharts: A visual formalism for complex systems, I propose to add an unlabelled arrow from a history state to its initial memory. This allows one to read the diagram only and tell the initial memory. It does not interfere with regular transitions as history cannot have any transitions (no TransitionStateMixin).

[tommens]

@Zinoex, thanks a lot for your interest in Sismic, your contributions and suggested fixes. Just out of curiosity, may we ask you how you are using (or intending to use) Sismic? It is always useful for us to have user feedback on the different ways and case studies in which Sismic is being used. Thanks.

[AlexandreDecan]

@Zinoex Thanks for this PR! I'll wait for your feedback before releasing the two pull requests in a new version of Sismic, in case there are other changes we would like to include as well.

[Zinoex]

Hi @tommens and @AlexandreDecan, it's part of a project for a course at UC Berkeley, where we use it to build and verify a new traffic light system. The current system is a central controller + wires to each signal. We intend to replace that with a controller in each light, where we then use Sismic to generate the logic for synchronization, light control, and health monitoring. We've bought some Raspberry Pis to deploy on, so I only develop a single model, which is supposed to run on each Raspberry Pi. We then use secure websockets to send events between each of the Pis. However, I'm also super happy that you can compose multiple statecharts, so you can run and test the system without manually wiring them together.

I don't have any plans in particular to develop features but if I stumble across any bugs in the next few weeks, I'll be sure to let you know or attempt to fix it myself.

[Zinoex]

If you want to follow the development, the repo is here: https://github.com/Zinoex/siren. We can also provide you with a copy of our paper when we've handed it in.

[AlexandreDecan]

Hello. Thanks for this feedback! It's nice to see new use-cases for Sismic :-)
And yes, I'm interested in the paper ;)

[AlexandreDecan]

FYI, I've just deployed Sismic 1.6.0 on PyPI with #95 and #96. Thanks again for these PRs!