Attempts at Curried On Poly

try10.scala

  class Curried[P, N <: Nat, L <: HList](p: P, args: L) extends Poly1{
    def yo[H](h: H)(implicit step: Step[P, L, H]) = h //aaarrrggg!!
  }

  trait Step[P, L <: HList, H]

  object Step{
    def apply[P, L <: HList, H](implicit step: Step[P, L, H]) = step

    implicit def first[P, R <: HList](implicit ev: Case[P, R], cons: hl.IsHCons[R]): Step[P, HNil, cons.H] =
      new Step[P, HNil, cons.H]{}

    implicit def mk[P, L <: HList, R <: HList, LR <: HList]
      (implicit prepend: hl.Prepend.Aux[L, R, LR],
                ev: Case[P, LR], 
                lcons: hl.IsHCons[L],
                cons: hl.IsHCons[R]): Step[P, L, cons.H] = new Step[P, L, cons.H]{}
  }

  trait CurriedBuilder[P <: Poly, N <: Nat] extends (P => Curried[P, N, HNil])

  object CurriedBuilder{
    def apply[P <: Poly, N <: Nat](implicit builder: CurriedBuilder[P, N]) = builder

    //we can prove that there exists some HList "L" of length "N" given a "P". But we can't prove that the first argument
    //to "L" is "H" above? Why?
    implicit def curBuilder[P <: Poly, N <: Nat, L <: HList](implicit ev: Case[P, L], length: hl.Length.Aux[L, N]) = 
      new CurriedBuilder[P, N]{
        def apply(p: P) = new Curried[P, N, HNil](p, HNil)
      }
  }

try11.scala

  class Curried[P, N <: Nat, L <: HList](args: L) extends Poly1{
    implicit def cont[A](implicit step: Step[P, L, A, N]) = use({a: A => step(a :: args)})
    def yo[A](implicit ste: Step[P, L, A, N]) = ste //called by itself, this fails so above fails as well.
  }

  trait Step[P, L <: HList, H, N <: Nat] extends DepFn1[H :: L]

  object Step extends LowPriorityStep{
    def apply[P, L <: HList, H, N <: Nat](implicit step: Step[P, L, H, N]) = step

    implicit def finCase[P, N <: Nat, L <: HList, OutL <: HList, H, T <: HList]
      (implicit ev: Case[P, OutL],
                reverse: hl.Reverse.Aux[H :: T, OutL],
                length: hl.Length.Aux[L, N],
                cons: hl.IsHCons.Aux[L, H, T]): Step[P, T, H, N] =
        new Step[P, T, H, N]{
          type Out = ev.Result

          def apply(l: H :: T) = ev(reverse(l))
        }
  }

  trait LowPriorityStep{
    implicit def nextCase[P, N <: Nat, L <: HList, RevL <: HList, R <: HList, LR <: HList]
      (implicit reverse: hl.Reverse.Aux[L, RevL],
                prepend: hl.Prepend.Aux[RevL, R, LR],
                ev: Case[P, LR],
                length: hl.Length.Aux[LR, N],
                cons: hl.IsHCons[R]) =
        new Step[P, L, cons.H, N]{
          type Out = Curried[P, N, cons.H :: L]

          def apply(h: cons.H :: L) = new Curried[P, N, cons.H :: L](h)
        }
  }

try6.scala

  class Curried[P <: Poly, N <: Nat, L <: HList](p: P, args: L) extends Poly1{
    implicit def next[H](implicit gen: (P, L) => Case[this.type, H :: HNil]): Case[this.type, H :: HNil] = gen(p, args)
  }

  object Curried{
    //later
    def apply[P <: Poly, N <: Nat, L <: HList](implicit ev: Case[P, L], length: hl.Length.Aux[L, N]) = new Curried[P, N, HNil](p, HNil)

    implicit def curryCase[C <: Poly, P <: Poly, N <: Nat, L <: HList, H, T <: HList, PL <: HList, OutL <: HList]
      (implicit unpack: Unpack3[C, Curried, P, N, L], 
                pre: hl.Prepend.Aux[L, H :: T, PL], 
                prepend: hl.Prepend.Aux[L, H :: HNil, OutL],
                ev: Case[P, PL], 
                length: hl.Length.Aux[PL, N]): (P, L) => Case.Aux[C, H :: HNil, Curried[P, N, OutL]] =
        (p: P, l: L) => new Case[C, H :: HNil]{
          type Result = Curried[P, N, OutL]

          val value = (h: H :: HNil) => new Curried[P, N, OutL](p, prepend(l, h))
        }

    implicit def finalCase[C <: Poly, P <: Poly, N <: Nat, L <: HList, H, PL <: HList]
      (implicit unpack: Unpack3[C, Curried, P, N, L],
                prepend: hl.Prepend.Aux[L, H :: HNil, PL], 
                ev: Case[P, PL], 
                length: hl.Length.Aux[PL, N]): (P, L) => Case.Aux[C, H :: HNil, ev.Result] = 
        (p: P, l: L) => new Case[C, H :: HNil]{
          type Result = ev.Result
          val value = (h: H :: HNil) => ev(prepend(l, h :: HNil))
        }
  }

Idea 35555: try creating an implicit PartialCase[L <: HList, R <: HList, N <: Nat]. Then we can base this type of thing on PartialCase or barring that (same issues as before?) We can do something along the lines of a ZipperCase?