class Ls [T](hd : Option[T], tl : Ls[T]){
    def foldr[ACC](acc: ACC,fun:(ACC,Option[T])=>ACC):ACC = {
        hd match {
            case None => acc
            case Some(x) => tl.foldr(fun(acc,Some(x)),fun)
        }
    }
    def concat(x: T):Ls[T] = {
        new Ls[T](Some(x),this)
    }
    override def clone() = {
        this.foldr[Ls[T]](new Ls[T](None,null),(acc: Ls[T],x:Option[T]) => x match{
            case None => acc
            case Some(y) => acc.concat(y)
        })
    }
    def len():Int = {
        foldr[Int](0,(acc: Int,x:Option[T]) =>
            x match{
                case None => acc
                case Some(y) => acc+1
            }
        )
    }
}


object Main extends App{
    println("test")
    val ls = new Ls[Int](Some(1),new Ls[Int](Some(2),new Ls[Int](None,null)))
    println(ls.concat(1).clone().len())
}