HList in Scala (v1 from Scala in depth)

HList.scala

// HList implementation
 
sealed trait HList
 
final case class HCons[H, T <: HList](head: H, tail: T) extends HList {
def ::[T](v : T) = HCons(v,this)
override def toString = head + " :: " + tail
}
 
final class HNil extends HList {
def ::[T](v : T) = HCons(v,this)
override def toString = "Nil"
}
 
object HList {
type ::[H, T <: HList] = HCons[H,T]
val :: = HCons
val HNil = new HNil
}
 
// Used as such:
 
import HList._
 
val x = "Hi" :: 5 :: false :: HNil
val one :: two :: three :: HNil = x