Scala-Options -> Type-variances, type bounds

Scala_functional

def position[A](list: List[A], element: A) = {
  val index: Int = list indexOf (element)
  if (index == -1) Nil
  else Just(index)
}

sealed abstract class Maybe[+A] {
  def isEmpty: Boolean

  def get: A

  def getOrElse[B >: A](default: B): B = {
    if(isEmpty) default else get
  }
}

final case class Just[A](value: A) extends Maybe[A] {
  override def isEmpty: Boolean = false

  override def get = value
}

case object Nil extends Maybe[Nothing] {
  override def isEmpty: Boolean = true

  override def get: Nothing = throw new NoSuchElementException("Nil.Get^^")
}

position(List("A", "B", "C"), "B").getOrElse(-1)

val strings: List[String] = List("A", "B")
val everything: List[Any] = strings
1 :: everything