gistfile1.scala

object Reckeys {
  import shapeless.{ HList, HNil, Id }, shapeless.Poly1, shapeless.record.FieldType, shapeless.ops.hlist.{ Mapper, Tupler }, shapeless.syntax.singleton._;
  object recordKeys extends Poly1 {
    implicit def caseAll[K, V] = at[FieldType[K, V]](ft => ??? : K)
  }

  def reckeys[L <: HList, P <: HList](ev: L)(implicit m: Mapper.Aux[recordKeys.type, L, P],
    t: Tupler[P]): t.type { type Out = t.Out } = t

}