List of options: equivalent of sequence in Scala?

Question

What is the equivalent of Haskell\'s sequence in Scala? I want to turn list of options into an option of list. It should come out as None if any of the options

Answer 1

Maybe this helps, as it traverses once only and use recursion

def sequence[A](a: List[Option[A]]): Option[List[A]] =
a match {
  case Nil => Some(Nil)
  case h :: rest => h.flatMap(x => sequence(rest).map(x :: _))
}