For a given F[_], a type level check that the HList L looks like F[A] :: F[B] :: F[C] :: HNil and fails to compile when it looks like F[A] :: SomeOtherType :: HNil

hlistOfFs.scala

  sealed trait IsDataType[F[_], L <: HList]
  object IsDataType {
    implicit def hnil[F[_]]: IsDataType[F, HNil] = new IsDataType[F, HNil] {}
    implicit def rest[F[_], H, T <: HList : ({type l[a] = IsDataType[F, a]})#l]: IsDataType[F, ::[F[H], T]] =
      new IsDataType[F, F[H] :: T] {}
  }