sealed class LinkedList : Iterable<LinkedList> {

    data class Node<out T>(val payload : T, var next : LinkedList = EmptyList) : LinkedList() {
        override fun toString() = payload.toString()
    }

    object EmptyList : LinkedList() {
        override fun toString() = ""
    }

    override fun iterator(): Iterator<LinkedList> = object :Iterator<LinkedList> {

        private var nextPointer = this@LinkedList

        override fun hasNext(): Boolean {
            return nextPointer is LinkedList.Node<*>
        }

        override fun next(): LinkedList {
            val cachedNextPointer = nextPointer
            if (cachedNextPointer is LinkedList.Node<*>) {
                nextPointer = cachedNextPointer.next
            }
            return cachedNextPointer
        }
    }
}

val nonEmptyList = LinkedList.Node(payload = "A", next = LinkedList.Node(payload = "B"))

fun main(args: Array<String>) {
    for (node in nonEmptyList) { // prints A B
        println(node)
    }
}