anchor.diff:      Added = sets:subtract(FilesSet, S#state.fileset),
       Removed = sets:subtract(S#state.fileset, FilesSet),
       NewState = S#state{fileset = FilesSet},
  -    {Added, Removed, NewState}.
  +    {ok, Added, Removed, NewState}.
  
positive.code: %%--------------------------------------------------------------------
  
  %% Operations
  
  empty_state() -> sets:new().
  
  
negative.code: 
  -vsn("1").
  %% API
  -export([start_link/0, dir_watched/0]).
  
  %% gen_server callbacks
  -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
  