anchor.diff:  from( ) ->
       { self(), make_ref() }.
   
  --spec wait( { pid(), reference() } ) ->
  +-spec wait( msg_token() ) ->
       any() | { error, timeout }.
   wait( Id ) ->
       receive
  
positive.code: 
  -spec enter_loop( string() | binary(),
                    [ string() | binary() ],
                    { pid(), reference() } ) ->
      { ok, { pid(), reference() } } | { error, term() }.
  enter_loop( Driver, Parameters, { Pid, Tag } ) ->
      case start_driver( Driver, Parameters ) of
          { ok, Port } ->
  
negative.code:     Pid ! { stop, From },
      wait( To ).
  
  -spec stop_async( pid() ) -> { ok, msg_token() }.
  stop_async( Pid ) ->
      { From, To } = from_to( self(), Pid ),
      Pid ! { stop, From },
  