// why doesn't this work?
data class NumberNode(val myData: Int, val next: NumberNode)


// represents that a linked list can either be empty,
// or a node with numeric data and a reference to
// the next such list

sealed class LinkedListNumbers {
    object Empty: LinkedListNumbers()
    data class Node(
        val myData: Int, 
        val next: LinkedListNumbers
    ): LinkedListNumbers()
}

val emptyNumberList = LinkedListNumbers.Empty
val list1   = LinkedListNumbers.Node(1, emptyNumberList)
val list21  = LinkedListNumbers.Node(2, list1)
val list321 = LinkedListNumbers.Node(3, list21)

println(list321)