anchor.diff:  handle_call(await, From, #{cycle := C, waiting := Waiting} = State) ->
     {noreply, State#{cycle := C - 1, waiting := [From | Waiting]}}.
   
  +%% @private
   -spec handle_cast(any(), state()) -> {noreply, state()}.
   handle_cast(_Request, State) ->
     {noreply, State}.
  +
  +%% @private
  +-spec handle_info(any(), state()) -> {noreply, state()}.
  +handle_info(_Msg, State) ->
  +  {noreply, State}.
  +
  +%% @private
  +-spec terminate(any(), state()) -> {ok, state()}.
  +terminate(_Msg, State) ->
  +  {ok, State}.
  +
  +%% @private
  +-spec code_change(any(), any(), state()) -> {ok, state()}.
  +code_change(_Msg, _From, State) ->
  +  {ok, State}.
   
   %%------------------------------------------------------------------------------
   %% Internal
  
positive.code: %% gen_server callbacks
  %%------------------------------------------------------------------------------
  
  -spec init(any()) -> {ok, state()}.
  init(N) ->
    State = #{ count   => N
  
negative.code: -export([ init/1
          , handle_call/3
          , handle_cast/2
          , handle_info/2
          , terminate/2
          , code_change/3
          ]).
  
  -type state() :: #{ count   => integer()
  