anchor.diff:  -type reason() :: any().
   
   handle_cast (_Request, State) -> {noreply, State}.
  -handle_info (_Info, State) -> {noreply, State}.
  +
  +handle_info (Message, State) ->
  +	io:format ("received: ~p~n", [Message]),
  +	{noreply, State}.
  +
   code_change (_OldVsn, State, _Extra) -> {ok, State}.
  
positive.code: 
  -export_type ([mvar/1]).
  -export ([create/2, new/2, new/1]).
  -export ([modify/2, with/2, read/1, write/2]).
  -export ([terminate/1]).
  
  -behaviour (gen_server).
  
negative.code: 	{ok, B} -> B;
  	{throw, Thrown} -> throw (Thrown) end.
  
  -spec modify_ (mvar(A), fun ((A) -> A)) -> ok. % IO throws X
  % Same as modify but don't return anything
  modify_ (Var, Modify) -> modify (Var, fun (A) -> {Modify (A), ok} end).
  
  -spec with (mvar(A), fun ((A) -> B)) -> B. % IO throws X, fun IO throws X
  % Execute Procedure with exclusive access to content but don't modify it.
  with (Var, Act) -> modify (Var, fun (A) -> {A, Act (A)} end).
  