ConsList.kl

//fun <A> nil(): ConsList<A> {
//    return ConsList.Nil<A>
//}

sealed class ConsList<A> : Iterable<A> {
    fun cons(value: A): ConsList<A> {
        return Cons(value, this);
    }

    fun isEmpty() : Boolean = this !is Nil

    fun size(): Int {
        tailrec fun recSize(xs: ConsList<A>, acc: Int): Int =
                if (xs is Cons<A>) recSize(xs.parent, acc + 1)
                else acc
        return recSize(this, 0)
    }

    override fun iterator(): Iterator<A> {
        return ConsIterator(this)
    }

    override fun toString(): String {
        val sb = StringBuilder("[")
        var self : ConsList<A> = this
        while (self is Cons<A>) {
            sb.append(self.value).append(",")
            self = self.parent
        }
        sb.setLength(sb.length - 1)
        sb.append("]")
        return sb.toString()
    }

    class Cons<A>(val value: A, val parent: ConsList<A>) : ConsList<A>()

    class  Nil<A> : ConsList<A>()

    private class ConsIterator<A>(var self: ConsList<A>) : AbstractIterator<A>() {
        override fun computeNext() {
            val current = self
            if (current !is Cons<A>)
                return done()

            setNext(current.value)
            self = current.parent
        }
    }
}