anchor.diff:  handle_call({post, Text}, _From, State) ->
       Status = post(Text, State),
       {reply, Status, State};
  +handle_call({is_logged_in}, _From, State) ->
  +    {reply, State#state.logged_in, State};
   handle_call(_Request, _From, State) ->
       {reply, unknown_command, State}.
   
  
positive.code: %% API
  -export([start_link/0,
           login/0,
           post/1]).
  
  %% gen_server callbacks
  -export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3]).
  
negative.code: 
  post(Text) ->
      gen_server:call(?MODULE, {post, Text}).
  
  is_logged_in() ->
      gen_server:call(?MODULE, {is_logged_in}).
  
  %%%===================================================================
  %%% gen_server callbacks
  