enum MyState: StateType {
    case State0, State1, State2
    case AnyState   // create case=Any

    init(nilLiteral: Void) {
        self = AnyState
    }
}

let machine = StateMachine<MyState, MyEvent>(state: .State0) { machine in

    machine.addRoute(.State0 => .State1)
    machine.addRoute(nil => .State2) { context in print("Any => 2, msg=\(context.userInfo)") }
    machine.addRoute(.State2 => nil) { context in print("2 => Any, msg=\(context.userInfo)") }

    // add handler (handlerContext = (event, transition, order, userInfo))
    machine.addHandler(.State0 => .State1) { context in
        print("0 => 1")
    }

    // add errorHandler
    machine.addErrorHandler { (event, transition, order, userInfo) in
        print("[ERROR] \(transition.fromState) => \(transition.toState)")
    }
}

// tryState 0 => 1 => 2 => 1 => 0
machine <- .State1
machine <- (.State2, "Hello")
machine <- (.State1, "Bye")
machine <- .State0  // fail: no 1 => 0

print("machine.state = \(machine.state)")

0 => 1
Any => 2, msg=Hello
2 => Any, msg=Bye
[ERROR] 1 => 0
machine.state = 1