anchor.diff:  close_port(_, return) -> ok;
   close_port(_, {net, _Writer, Closer}) -> Closer();
   close_port(_, {exec, _Writer, Closer}) -> Closer();
  +close_port(_, {serial, _Writer, Closer}) -> Closer();
   close_port(Data, {http, Final}) -> Final(Data);
   close_port(_, Fd) -> file:close(Fd).
   
  
positive.code: 
  %% last member find
  -spec last_output(any()) -> any().
  last_output(L) when is_list(L) -> last_output(lists:last(L));
  last_output(F) when is_function(F) -> last_output(F());
  last_output(X) -> X.
  
  
negative.code:     SerialPort = serial:start(Options),          
      fun F(_N, Meta) ->
          {F, {serial,
              fun (Data) -> SerialPort ! {send, Data}, ok end,
              fun () -> ok end
          }, [{output, serial} | Meta]}
      end.
  
  