anchor.diff:      {reply, Status, NewState};
   handle_call({post, Feed, Text}, _From, State) ->
       Status = post(Feed, Text, State),
  +    {reply, Status, State};
  +handle_call({comment, PostID, Text}, _From, State) ->
  +    Status = comment(PostID, Text, State),
       {reply, Status, State};
   handle_call({is_logged_in}, _From, State) ->
       {reply, State#state.logged_in, State};
  
positive.code:          get_posts/1,
           login/0,
           post/2,
           is_logged_in/0
          ]).
  
  
negative.code: 
  post(Feed, Text) ->
      gen_server:call(?MODULE, {post, Feed, Text}).
  
  comment(PostID, Text) ->
      gen_server:call(?MODULE, {comment, PostID, Text}).
  
  is_logged_in() ->
      gen_server:call(?MODULE, {is_logged_in}).
  