code: func rlConcat(cnx redis.Conn, src, dest string) error {
  	data, err := cnx.Do("RPOPLPUSH", src, dest)
  	if err != nil {
  		return err
  	}
  	if data == nil {
  		return redis.ErrNil
  	}
  
  	return nil
  }
docs: // Concat implementation using RPOPLPUSH, compatible
  // with the behaviour of Processor.Queue.