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

If you want a solution for just List and Option rather a general monad then following will do the job,

def sequence[T](l : List[Option[T]]) = 
  if (l.contains(None)) None else Some(l.flatten)

REPL session,

scala> sequence(List(Some(1), None, Some(2)))
res2: Option[List[Int]] = None

scala> sequence(List(Some(1), Some(2), Some(3)))
res3: Option[List[Int]] = Some(List(1, 2, 3)) 

Update 20/8/2014

Just use Scalaz ...