转自：http://www.cnblogs.com/yourihua/archive/2012/05/13/2497776.html

代码如下：

-module(npc).

-behaviour(gen_fsm).

%% API
-export([start_link/0]).

%% gen_fsm callbacks
-export([init/1, static/2, moving/2, handle_event/3, 
	handle_sync_event/4, handle_info/3, terminate/3, code_change/4]).

-export([hero_join/0, hero_leave/0]).

-define(SERVER, ?MODULE).

-record(npc, {state}).

start_link() ->
	gen_fsm:start_link({local, ?SERVER}, ?MODULE, [], []).

%% 初始化NPC为静止状态
init([]) ->
	io:format("init...~n"),
	State = #npc{state = static},
	io:format("init State: ~p~n", [State]),
	{ok, static, State}.

%% 英雄进入视野
hero_join() ->
	gen_fsm:send_event(?SERVER, hero_join).

%% 英雄离开视野
hero_leave() ->
	gen_fsm:send_event(?SERVER, hero_leave).

%% 静止状态下，接受来自客户端的事件
static(Event, State) ->
	case Event of
		hero_join -> %% 英雄进入视野
			do_moving(), %% 执行动作
			NewState = State#npc{state = moving},
			io:format("npc set state: ~p~n", [NewState]),
			{next_state, moving, NewState}
	end.

%% 移动状态下，接受来自客户端的事件
moving(Event, State) ->
	case Event of
	hero_leave -> %% 英雄离开视野
		do_static(), %% 执行动作
		NewState = State#npc{state = static},
		io:format("npc set state: ~p~n", [NewState]),
		{next_state, static, NewState}
	end.

handle_event(_Event, StateName, State) ->
	{next_state, StateName, State}.

handle_sync_event(_Event, _From, StateName, State) ->
	Reply = ok,
	{reply, Reply, StateName, State}.

handle_info(_Info, StateName, State) ->
	{next_state, StateName, State}.

terminate(_Reason, _StateName, _State) ->
	ok.

code_change(_OldVsn, StateName, State, _Extra) ->
	{ok, StateName, State}.

%% NPC 开始移动，进入移动状态
do_moving() ->
	io:format("npc beigin moving...~n").

%% NPC 停止移动，进入静止状态
do_static() ->
	io:format("npc stop moving, join static...~n").

http://10lover10.blog.51cto.com/6266102/1098174

http://erlshawn.wordpress.com/2011/05/12/gen_fsm/

http://www.iteye.com/topic/658210