Partial Functions in Scala

PartialFunction.scala

val doubleEvenNumbers = new PartialFunction[Int, Int] {
  def isDefinedAt(x: Int) = x % 2 == 0
  def apply(v1: Int) = v1 * 2
}

val tripleOddNumbers = new PartialFunction[Int, Int] {
  def isDefinedAt(x: Int) = x % 2 != 0
  def apply(v1: Int) = v1 * 3
}

val doubleOrTriple = doubleEvenNumbers orElse tripleOddNumbers

doubleOrTriple(3) // => 9
doubleOrTriple(4) // => 8