/* Describes finete state machine objects */
%:-module fsm.
%:-public fsm/3, fsm_transition/2, fsm_transiton_backtrackable/2.
%:-public test_fsm1, test_fsm12.
 
fsm(StateList, InitialState, FSM):-
	assignable(FSM , fsm(StateList,InitialState)).
fsm_transition(FSM,Event):-
	FSM => fsm(StateList,CurrentState),
	fsm_lookup(StateList,Event,CurrentState,NextState),!,
	write(CurrentState-Event-NextState),nl,
	FSM <+ fsm(StateList,NextState).
fsm_transition_backtrackable(FSM,Event):-
	FSM => fsm(StateList,CurrentState),
	fsm_lookup(StateList,Event,CurrentState,NextState),
	write(CurrentState-Event-NextState),nl,
	FSM <= fsm(StateList,NextState).
fsm_lookup([State-Event-NextState|_],Event,State, NextState).
fsm_lookup([_|StateList],Event,State, NextState):-
	fsm_lookup(StateList,Event,State, NextState).
fsm_state(FSM,State):-
	FSM => fsm(_,State).
	
/* fsm transition example */
%:-public test_fsm.
test_fsm1:-
	fsm([	red-0-red,red-1-green,red-2-red,
		yellow-0-red,yellow-1-green,yellow-2-red,
		green-0-yellow,green-1-yellow,green-2-red],
		red, FSM),
	fsm_transition(FSM,0),
	fsm_state(FSM,State1), State1 = red,
	fsm_transition(FSM,1),
	fsm_state(FSM,State2), State2 = green,
	fsm_transition(FSM,1),
	fsm_state(FSM,State3), State3 = yellow,
	fsm_transition(FSM,2),
	fsm_state(FSM,State4), State4 = red,
	true.
 

/* non deterministic fsm transition */
test_fsm2:-
	fsm([	red-0-red,red-0-green,red-2-red,
		yellow-0-red,yellow-1-green,yellow-2-red,
		green-0-yellow,green-1-yellow,green-2-red],
		red, FSM),
	test_fsm2(FSM).

test_fsm2(FSM):-
	fsm_transition_backtrackable(FSM,0),
	fsm_state(FSM,State),	% State is red or green
	write(State),nl,
	State == green.		% if State == red, fail