validateGen.scala

// libraryDependencies ++= Seq(
//  "org.scalaz" %% "scalaz-core" % "7.1.0",
//  "com.chuusai" %% "shapeless" % "2.0.0",
//  "org.typelevel" %% "shapeless-scalacheck" % "0.3",
//  "org.typelevel" %% "shapeless-spire" % "0.3",
//  "org.typelevel" %% "shapeless-scalaz" % "0.3"
// )


import shapeless._, contrib.scalaz._, syntax.std.tuple._
import syntax.std.function._, ops.function._
import shapeless.ops.hlist._
import Poly._

type Va[A] = Validation[String, A]
type VaNel[A] = ValidationNel[String, A]

object toValidationNel extends Poly1 {
  implicit def apply[T] = at[Va[T]](_.toValidationNel)
}

def validateGen[P <: Product, F, L1 <: HList, L2 <: HList, L3 <: HList, R, Lx, Out <: Product](params: P)(block: F)(
  implicit
  gen: Generic.Aux[P, L1],
  uc1: UnaryTCConstraint[L1, Va],
  mp:  Mapper.Aux[toValidationNel.type, L1, L2],
  seq: Sequencer.Aux[L2, VaNel[L3]],
  tup: Tupler.Aux[L3, Out]
  // fn:  FnToProduct.Aux[F, Out => R]
) = {
  sequence(gen.to(params).map(toValidationNel)).map(_.tupled)//.map(block.toProduct)
}