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/*
 * Originally adapted from shapeless-contrib scalaz
 * https://github.com/typelevel/shapeless-contrib/blob/v0.4/scalaz/main/scala/traverse.scala
 *
 */
package cats.sequence

import shapeless._
import shapeless.ops.hlist._

sealed trait Traverser[L <: HList, P] {
  type Out
  def apply(in: L): Out
}

object Traverser {
  type Aux[L <: HList, P, Out0] = Traverser[L, P] { type Out = Out0 }

  implicit def mkTraverser[L <: HList, P, S <: HList](
    implicit
      mapper: Mapper.Aux[P, L, S],
      sequencer: Sequencer[S]
  ): Aux[L, P, sequencer.Out] =
    new Traverser[L, P] {
      type Out = sequencer.Out
      def apply(in: L): Out = sequencer(mapper(in))
    }
}

trait TraverseFunctions {
  def traverse[L <: HList](in: L)(f: Poly)
    (implicit traverser: Traverser[L, f.type]): traverser.Out = traverser(in)

}

trait TraverseOps extends {
  implicit class withTraverse[L <: HList](self: L) {
    def traverse(f: Poly)
      (implicit traverser: Traverser[L, f.type]): traverser.Out = traverser(self)
  }
}