transform a MemberIn

MemberInTransform.scala

object Test {
  import cats._
  import cats.data._
  import cats.implicits._

  import org.atnos.eff._
  import org.atnos.eff.all._
  import org.atnos.eff.syntax.all._

  case class Address()
  case class Person(address: Address)

  object Main extends App {

    type per[E] = State[Person, ?] |= E
    type add[E] = State[Address, ?] |= E
    type err[E] = Xor[String, ?] |= E

    implicit def AddressPersonNaturalTransformation: (State[Address, ?] ~> State[Person, ?]) =
      new (State[Address, ?] ~> State[Person, ?]) {
        def apply[X](s: State[Address, X]) =
          State[Person, X] { person =>
            val (address, x) = s.run(person.address).value
            (person.copy(address = address), x)
          }
     }
    
    def updatePerson[E: per: err]: Eff[E, Unit] = for {
      _ <- updateAddress[E](implicitly[per[E]].transform, implicitly[err[E]])
    } yield ()

    def updateAddress[E: add: err]: Eff[E, Unit] = for {
      _ <- get
    } yield ()
  }
}