An FSM is used to represent an instance of a finite state machine which has a transition function represented by an instance of StateEngine. An instance of an FSM may be created either by calling StateEngine.makeFSM( startState ) on a state engine, or by extending FSMImpl and using a constructor. Using FSMImpl as a base class is convenient if additional state is associated with the FSM beyond that encoded by the current state. This is especially convenient if an action needs some additional information. For example, counters are best handled by special actions rather than encoding a bounded counter in a state machine. It is also possible to create a class that implements the FSM interface by delegating to an FSM instance created by StateEngine.makeFSM.