bull.scala

import shapeless._

object Bullshit {
  sealed abstract class Size[T](val size:Int)

  object Size{
    implicit object sizeForString extends Size[String](9)
    implicit object sizeForInt extends Size[Int](4)
    implicit object sizeForFloat extends Size[Float](7)
  }
  
  type stuff = String :: Int :: Float :: HNil
  
  def size[T <: HList](implicit s : ToSize[T]) = s()
  
  //doesn't compile
  val c = size[stuff]
  val d = implicitly[ToSize[stuff]]
  
  trait ToSize[-L <: HList] {
    def apply() : Int
  }

  object ToSize {
    implicit val toSize0 = new ToSize[HNil] {
      def apply() = 0 
    }
    
    implicit def toSizeSucc[T, L <: HList](implicit toSizeN : ToSize[L], s : Size[T]) = new ToSize[T :: L] {
      def apply() = toSizeN() + s.size
    }
  }
  
  //compiles
  //val c = size[stuff]          
  //val d = implicitly[ToSize[stuff]]
}