future-zip-n.scala

import scala.concurrent.{ ExecutionContext, Future }
import shapeless._, ops.tuple.{ IsComposite, LeftFolder, Prepend }

object zipAndAdd extends Poly2 {
  implicit def only[B, A](implicit p: Prepend[B, Tuple1[A]], executor: ExecutionContext) =
    at[Future[B], Future[A]] {
      (fb, fa) => fb.zip(fa).map { case (b, a) => p(b, Tuple1(a)) }
    }
}

def zipN[P, FH, H, T, O](p: P)(implicit
  comp: IsComposite.Aux[P, FH, T],
  ev: FH <:< Future[H],
  folder: LeftFolder.Aux[T, Future[Tuple1[H]], zipAndAdd.type, O],
  executor: ExecutionContext
): O = folder(comp.tail(p), comp.head(p).map(Tuple1(_)))