Hierarchical State Machine

This hierarchial state machine (HSM) resembles a UML statechart, written in dart. States are oranized in parent/child relationships, allowing common event handling to be performed by more generic, containing states. This machine also supports parallel or "Orthogonal regions".

The most important information can be found in the EventHandler class:

/// Order of operations for the following state, assuming event T1 is fired and
/// s11 is the current state.
///     1) T1 delivered to s1
///     2) Guard g() is called. If it returns false, stop.
///     3) a(), b(), t(), c(), d(), e()
/// ┌──────────────────────────|s|──────────────────────────┐
/// │┌────|s1|────┐                    ┌────|s2|───────────┐│
/// ││exit:b()    │                    │entry:c()          ││
/// ││┌──|s11|──┐ │                    │-*:d()->┌──|s21|──┐││
/// │││exit:a() │ │--T1{guard:g(),     │        │entry:e()│││
/// │││         │ │      action:t()}-->│        │         │││
/// ││└─────────┘ │                    │        └─────────┘││
/// │└────────────┘                    └───────────────────┘│
/// └───────────────────────────────────────────────────────┘