hasSubsequence.scala

def hasSubsequence[A](sup: List[A], sub: List[A]): Boolean = {
  def loop[A](supRev: List[A], subRev: List[A], isSubSequence: Boolean): Boolean = supRev match {
    case Nil => {
      subRev match {
        case Nil => isSubSequence
        case _ => false
      }
    }
    case Cons(x,xs) => subRev match {
      case Nil => isSubSequence
      case Cons(x2, xs2) => {
        if(x == x2) loop(xs, xs2, true)
        else loop(xs, subRev, false)
      }
    }
  }
  loop(sup, sub, false)
}