That's really interesting. This seems like it would be a really good approach to combine something like an otherwise pure finite state machine, but with state transitions that rely on communicating with external systems.

Normally I emit tokens to a stack which are consumed by an interpreter but then it's a bit awkward to feed the results back into the FSM, it feels like decoupling just for the sake of decoupling even though the systems need to be maintained in parallel.

I'll have to explore this approach, thank you!