fold

class Ls [T](head: T,tail: Ls[T]){
    val tl = tail
    val hd = head
    def foldr[ACC](acc: ACC,fun:(ACC,T)=>ACC):ACC = {
      if (tl==null){
        fun(acc,hd)
      }else{
         tl.foldr(fun(acc,hd),fun)
      }
    }
}
object Main extends App{
    println("test")
    val ls = new Ls[Int](1,new Ls[Int](2,new Ls[Int](3,null)))
    println(ls.foldr[Int](0,(acc:Int,x:Int) => acc+x+1))
}