sealed class List<out E>
object Empty: List<Nothing>() {
    override fun toString()= "[]"
}
data class Cons<E>(val head: E, val tail: List<E>): List<E>() {
    override fun toString(): String = "$head :: $tail"
}


fun main() {
    val myList1 = Empty
    val myList2 = Cons(1, myList1)
    val myList3 = Cons(2, myList2)
    println("myList1: $myList1")
    println("myList2: $myList2")
    println("myList3: $myList3")
}