object Patterns {
  ('1', "1") match {
    case (digit, str) => true
    case _ => false
  }

  val xs = List('2' -> "ABC", '3' -> "DEF")

  xs filter {
    case (digit, str) => true
    case _ => false
  }
  
  def sum(xs: List[Int]): Int = xs match {
    case Nil => 0
    case x :: xs1 => x + sum(xs1)
  }
  
  def len[T](xs: List[T]): Int = xs match {
    case _ :: xs1 => 1 + len(xs1)
    case Nil => 0
  }
  
  final def sameLength[T](xs: List[T], ys: List[T]): Boolean = xs match {
    case _ :: xs1 =>
      ys match {
        case _ :: ys1 => sameLength(xs1, ys1)
        case _ => false
      }
    case _ => ys.isEmpty
  }
}