hlist-dotty.scala

import scala.language.higherKinds
object hlists {
  sealed abstract class HList {
    type Merge[L <: HList] <: HList
    
    def merge[L <: HList](l: L): Merge[L]
  }
  final case class HCons[H, T <: HList](head : H, tail : T) extends HList {
    type Merge[L <: HList] = HCons[H, tail.Merge[L]]
    
    def merge[L <: HList](l: L): Merge[L] = HCons(head, tail.merge(l))
  }
  sealed trait HNil extends HList {
    type Merge[L <: HList] = L
    
    def merge[L <: HList](l: L): Merge[L] = l
  }
  final val HNil: HNil = { case object HNil extends HNil; HNil }
}

object test {

  import hlists._
  val merged: hlists.HCons[Int,hlists.HCons[String,hlists.HNil]] = hlists.HCons.apply[Int, hlists.HNil](42, hlists.HNil).merge[hlists.HCons[String,hlists.HNil]](hlists.HCons.apply[String, hlists.HNil]("foo", hlists.HNil));
}