HList in Kotlin, but better!

hlist.kt

sealed class HList {
    object HNil : HList()
    data class HNode<V, T : HList>(val value: V, val next: T) : HList()
    data class HPlus<H1 : HList, H2 : HList>(val h1: H1, val h2: H2) : HList() // note this!
}