code: func (f *FST) AcceptWithVal(addr int, b byte) (int, uint64) {
  	s, err := f.decoder.stateAt(addr, nil)
  	if err != nil {
  		return noneAddr, 0
  	}
  	_, next, output := s.TransitionFor(b)
  	return next, output
  }
docs: // AcceptWithVal returns the next state for this Automaton on input of byte b
  // and also returns the output value for the transition