After playing with my overloads library and trying to apply it to FSM I realized that some metaprogramming can be replaced with natural overload resolution rules. After realizing it, I come to conclusion that simple FSM can be implemented as a set of call operators and a list of states. Each call operator represents a transition and follows this pattern: NewState operator()(State,Event) const; Transition functions are generated in process_event function on first call (in a constructor of static variable, for example). Each function extracts current state from StatesAsVariant (boost::variant of all states): template<class StatesAsVariant, class State, class Event> void transition(FSM& fsm, StatesAsVariant states, Event event) { states = fsm( get<State>(states), event); // select best transition // according to overload // resolution rules } The only metaprogramming algorithm is for_each<States> to initialize transition table for the event. Comments? -- Alexander Nasonov