Flattening deeply nested tuples with Shapeless

tuple-flatten.scala

import shapeless._

trait Flatten[I, O <: HList] {
  def apply(i: I): O
}

trait FlattenLow {
  implicit def otherFlatten[I] = new Flatten[I, I :: HNil] {
    def apply(i: I) = i :: HNil
  }
}

object FlattenHigh extends FlattenLow {
  implicit object hnilFlatten extends Flatten[HNil, HNil] {
    def apply(i: HNil) = HNil
  }

  implicit def hlistFlatten[H, T <: HList, HO <: HList, TO <: HList, O <: HList](implicit
    hev: Flatten[H, HO],
    tev: Flatten[T, TO],
    pre: PrependAux[HO, TO, O]
  ) = new Flatten[H :: T, O] {
    def apply(i: H :: T) = pre(hev(i.head), tev(i.tail))
  }

  implicit def tupleFlatten[P <: Product, L <: HList, O <: HList](implicit
    lev: HListerAux[P, L],
    fev: Flatten[L, O]
  ) = new Flatten[P, O] {
    def apply(i: P) = fev(lev(i))
  }
}

import FlattenHigh._

def flatten[I, O <: HList](i: I)(implicit fev: Flatten[I, O], tev: Tupler[O]) = fev(i).tupled

val (a, b, c, d, e) = flatten((('a', "b"), ((3, 'd), 5.0)))
// Prints the following:
// a: Char = a
// b: String = b
// c: Int = 3
// d: Symbol = 'd
// e: Double = 5.0