A hierarchical finite state machine with support parent child relationships and transition enforcement. Based on Cássio Souza's ActionScript 3 one https://github.com/cassiozen/AS3-State-Machine which I ported to Lua with some modifications https://github.com/JesterXL/Lua-Corona-SDK-State-Machine that I've incorporated into the Dart one. There are existing state machines in Dart pub, but the Game ones had too many dependencies and the others were too hard to learn quickly.