anchor.diff:  -define(HEART_PORT_NAME, heart_port).
   
   -record(state,{port :: port(),
  -               cmd  :: [] | binary()}).
  +               cmd  :: [] | binary(),
  +               callback :: 'undefined' | {module(), function()}}).
   
   %%---------------------------------------------------------------------
   
  
positive.code:     end.
  
  loop(Parent, #state{port=Port}=S) ->
      _ = send_heart_beat(Port),
      receive
  	{From, set_cmd, NewCmd0} ->
  	    Enc = file:native_name_encoding(),
  
negative.code: 	{'EXIT', Port, badsig} ->  % we can ignore badsig-messages!
  	    loop(Parent, S);
  	{'EXIT', Port, _Reason} ->
  	    exit({port_terminated, {?MODULE, loop, [Parent, S]}});
  	_ -> 
  	    loop(Parent, S)
      after
  