anchor.diff:  %%                                      {stop, Reason, State}
   %% Description: Handling call messages
   %%--------------------------------------------------------------------
  -handle_call(_Request, _From, State) ->
  -    Reply = ok,
  -    {reply, Reply, State}.
  +handle_call(stop, _From, State) ->
  +    State#state.acceptor ! stop,
  +    {stop, stopped, ok, State}.
   
   %%--------------------------------------------------------------------
   %% Function: handle_cast(Msg, State) -> {noreply, State} |
  
positive.code: %%--------------------------------------------------------------------
  start_link(Port, Service, HandlerModule) when is_integer(Port), is_atom(HandlerModule) ->
      gen_server:start_link({local, ?SERVER}, ?MODULE, {Port, Service, HandlerModule}, []).
  
  %%====================================================================
  %% gen_server callbacks
  
negative.code: -behaviour(gen_server).
  
  %% API
  -export([start_link/3, stop/1]).
  
  %% gen_server callbacks
  -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
  