Converting an example to HList

[Peter Schmitz]

I don't know if this is the right place to ask but I am got stuck with instanceOf casts.

Here a minimized example:

Say I have a base trait with some abstract members:

  trait C {

    type M

    type A

    val upt: A => M => M

  }

And two examples instances:

  object C1 extends C {
    case class M(s: String)
    case class A(c: Char)
    val upt: A => M => M = { case A(c) => m => m copy (s = m.s + c) }
  }


  object C2 extends C {
    case class M(l: Long)
    case class A(i: Int)
    val upt: A => M => M = { case A(i) => m => m copy (l = m.l + i) }
  }

Now I want to wrap a list of C's into a new class CS:

  class CS(val cSubs: Seq[C]) extends C {
    case class M(mSubs: Seq[C#M])
    sealed trait A
    case class Asub[A0 <: C#A](idx: Int, aSub: A0) extends A
    val upt: A => M => M = {
      case Asub(idx, aSub) =>
        m => m copy (mSubs = m.mSubs.zip(cSubs).zipWithIndex map {
          case ((mSub, cSub), `idx`) => cSub.upt(aSub.asInstanceOf[cSub.A])(mSub.asInstanceOf[cSub.M])
          case ((mSub, cSub), _)     => mSub
        })

    }
  }

Don't wonder where the Asub(idx, aSub) instances finally come from, this is a minimized example.

For example I can run the following lines:

  val c1m1 = C1.M("Hey")
  val c1m2: C1.M = C1.upt(C1.A('!'))(c1m1)

  val cs = new CS(Seq(C1, C2))
  val csm1 = cs.M(Seq[C#M](C1.M("Hey"), C2.M(42L)))
  cs.upt(cs.Asub(0, C1.A('!')))(csm1)
  cs.upt(cs.Asub(1, C2.A(8)))(csm1)

But how can I use a HList instead of a Seq to get rid of this instanceOf? I tried but failed. I started with ensuring that every element in an argument HList conforms to type C:

  trait ConformsTo[L <: HList, T]
  object ConformsTo {
    implicit def hnil[X]: HNil ConformsTo X = null
    implicit def cons[X, X0 <: X, T <: HList](implicit ev: T ConformsTo X): (X0 :: T) ConformsTo X = null
  }


  object CS {
    def apply[L <: HList](l: L)(implicit conforms: L ConformsTo C) = new CS(l)
  }

  class CS[L <: HList](val l: L) extends C { ... }

Now I got stuck with mapping and zipWithIndex and modelling case class Asub(nat: Nat, ...) ....

I appreciate any ideas.

Thank you!

Peter