07.Hint

The signature of traverse is def traverse[E,A,B](es: List[A])(f: A => Either[E, B]): Either[E, List[B]], and the signature of sequence is def sequence[E,A](es: List[Either[E, A]]): Either[E, List[A]]. In your implementation, you can pattern-match the list and use explicit recursion or use foldRight to perform the recursion for you.