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: write (Var, Value) -> modify (Var, fun (A) -> {Value, A} end).
  
  -spec terminate (mvar(_)) -> ok. % IO
  % Terminate mvar. Its finalizer will be executed. Future accesses to this mvar will fail, although repeated termination is fine.
  terminate (Var) -> catch gen_server:call (Var, stop), ok.
  
  % gen_server callbacks %
  
  