gistfile1.scala

scala> val l = List(1,2,3)
l: List[Int] = List(1, 2, 3)

// pattern matching
scala> l match {
     |   case s if s.forall(even(_)) => Some(l)
     |   case _ => None
     | }
res37: Option[List[Int]] = None

// better
scala> Some(l) filter (_.forall(even))
res38: Option[List[Int]] = None

scala> val l = List(2, 4, 6)
l: List[Int] = List(2, 4, 6)

scala> Some(l) filter (_.forall(even))
res39: Option[List[Int]] = Some(List(2, 4, 6))

scala> List(1, 2, 3).forall(even).guard[Option](l)
res2: Option[List[Int]] = None

scala> List(2, 4).forall(even).guard[Option](l)   
res3: Option[List[Int]] = Some(List(1, 2, 3))

cool ..