function, PartialFunction, AddPositivePartialFunction

gistfile1.scala

object ScalaHackSession {
  object AddPositivePartialFunction extends PartialFunction[(Double, Double), Double] {
    override def isDefinedAt(abTuple: (Double, Double)): Boolean = abTuple._1 > 0 && abTuple._2 > 0
    override def apply(abTuple: (Double, Double)): Double = abTuple._1 + abTuple._2
  }

  AddPositivePartialFunction(2,3)                 //> res0: Double = 5.0
  AddPositivePartialFunction.isDefinedAt(-2, -3)  //> res1: Boolean = false

}