map_with.scala

package shiplis

import shapeless._, poly._, ops.hlist._

object MapWith
{
  object Apply
  extends Poly2
  {
    implicit def c[A, B, R, Tail <: HList, F <: Poly2]
    (implicit cse: poly.Case2.Aux[F, A, B, R])
    : Case2.Aux[this.type, B, ((A, F), Tail), ((A, F), R :: Tail)] =
      at[B, ((A, F), Tail)] {
        case (b, ((a, f), z)) =>
          (a, f) -> ((cse(a, b)) :: z)
      }
  }
}

final class MapWithSyntax[L <: HList](self: L)
{
  def mapWith[A, F <: Poly2, R](f: F, a: A)
  (implicit folder:
    RightFolder.Aux[L, ((A, F), HNil), MapWith.Apply.type, ((A, F), R)]) =
    folder(self, ((a, f), HNil: HNil))._2
}

trait ToMapWithSyntax
{
  implicit def ToMapWithSyntax[A <: HList](a: A) =
    new MapWithSyntax(a)
}

object map1
extends Poly2
{
  implicit def cse[L <: HList, F <: Poly1, R <: HList]
  (implicit mapper: Mapper.Aux[F, L, R]) =
    at[L, F] {
      case (l, _) => mapper(l)
    }
}

object f1
extends Poly2
{
  implicit def cse = at[(Int, Int), Int] {
    case ((b, c), a) => a * b + c
  }
}

object f2
extends Poly1
{
  implicit def cse = at[Int](a => s"1: $a")
}

object f3
extends Poly1
{
  implicit def cse = at[Int](a => a * 20)
}

class MapWithSpec
extends org.specs2.Specification
with ToMapWithSyntax
{
  def is = s2"""
  apply a Poly with additional fixed args to a HList $argmap
  apply a HList of Polys to each element of another HList $funmap
  """

  def argmap = {
    val h = 1 :: 2 :: 3 :: HNil
    h.mapWith(f1, (5, 4)) must_== 9 :: 14 :: 19 :: HNil
  }

  def funmap = {
    val h = 1 :: 2 :: 3 :: HNil
    val funs = f3 :: f2 :: f3 :: HNil
    val r = funs.mapWith(map1, h)
    val l1 = 20 :: 40 :: 60 :: HNil
    val l2 = "1: 1" :: "1: 2" :: "1: 3" :: HNil
    r must_== l1 :: l2 :: l1 :: HNil
  }
}