gistfile1.scala

import shapeless._

trait TypeValue[A, R] {
  def apply(): R
}

trait Size[A] extends TypeValue[A, Int]
 
implicit val shortSize = new Size[Short] {
  def apply() = 2
}
 
implicit val intSize = new Size[Int] {
  def apply() = 4
}
 
implicit val doubleSize = new Size[Double] {
  def apply() = 8
}

def sizeOf[A](implicit size: Size[A]) = size()

trait Name[A] extends TypeValue[A, String]

implicit val intName = new Name[Int] {
  def apply() = "Int"
}

implicit val doubleName = new Name[Double] {
  def apply() = "Double"
}

def nameOf[A](implicit name: Name[A]) = name()
 
sizeOf[Int] == 4
nameOf[Double] == "Double"

type FixReturn[R] = ({ type λ[A] = TypeValue[A, R] })#λ[_]
 
trait HListTypeMapper[L <: HList, R, F[_] <: FixReturn[R]] {
  def tmap(): List[R]
}
 
implicit def HNilTypeMapper[R, F[_] <: FixReturn[R]] = new HListTypeMapper[HNil, R, F] {
  def tmap() = Nil
}
 
implicit def hlistTypeMapper[H, T <: HList, R, F[_] <: FixReturn[R]](implicit typeValue: F[H], tailMapper: HListTypeMapper[T, R, F]) = 
  new HListTypeMapper[H :: T, R, F] {
    def tmap() = typeValue() :: tailMapper.tmap()
  }
 
def tmap[L <: HList, R, F[_] <: FixReturn[R]](implicit mapper: HListTypeMapper[L, R, F]): List[R] = mapper.tmap()
 
tmap[Int :: Double :: Short :: Int :: HNil, Int, Size] == List(4, 8, 2, 4)
tmap[Int :: String :: Short :: Int :: HNil, Int, Size] // doesn't compile. there's no implicit Size[String]
tmap[Int :: Double :: Int :: Int :: HNil, String, Name] == List("Int", "Double", "Int", "Int")
tmap[Int :: Double :: Short :: Int :: HNil, String, Name] // doesn't compile. there's no implicit Name[Short]