gistfile1.scala

import scalaz._
import Scalaz._
import effects._

trait Request
trait Response

case class WebState(_request: Request, _response: Response)

sealed trait Web[A] extends NewType[Web.T[A]]

object Web {
  type I[A] = IterVM[IO, String, A]
  type T[A] = StateT[I, WebState, Option[Validation[Response, A]]]

  def apply[A](a: T[A]): Web[A] = new Web[A] {
    val value = a
  }

  implicit def IterVMPure[M[_]: Pure, E] = new Pure[({ type λ[α] = IterVM[M, E, α] })#λ] {
    import IterV._
    def pure[A](a: ⇒ A): IterVM[M, E, A] = DoneM(a, Empty[E])
  }

  implicit def pureWeb: Pure[Web] = new Pure[Web] {
    def pure[A](a: ⇒ A): Web[A] = {
      val b = some(a.success[Response])
      val c = b.pure[I]
      Web(c.pure[T]) // <-- fails to compile with "could not find implicit value for parameter p: scalaz.Pure[Web.T] even though there is a Pure[StateT] available
    }
  }
}