A clever use of unapply to get syntax on Scalaz process for error handling

Syntax.scala

package shajra.extn.scalaz.stream


import scalaz.{ Bind, Traverse, Unapply }
import scalaz.stream.Process


trait Syntax {

  implicit class ProcessSyntax[F[_], A](self: Process[F, A]) {

    def through[B](c: Channel[F, A, B]): Process[F, B] =
      ProcessFunctions.throughChannel(self, c)

  }

  case class ProcessMSyntax[F[_], MM[_], A]
      (self: Process[F, MM[A]], trav: Traverse[MM]) {

    def throughM[MB]
        (c: Channel[F, A, MB])
        (implicit uBind: Unapply[Bind, MB] { type M[X] = MM[X] })
        : Process[F, MM[uBind.A]] = {
      val substC = uBind.leibniz.subst[Channel[F, A, ?]](c)
      ProcessFunctions.throughChannelM(self, substC)(uBind.TC, trav)
    }

  }

  implicit def processSyntax[F[_], MA]
      (p: Process[F, MA])
      (implicit uTrav: Unapply[Traverse, MA])
      : ProcessMSyntax[F, uTrav.M, uTrav.A] =
    ProcessMSyntax(uTrav.leibniz.subst[Process[F, ?]](p), uTrav.TC)

}


object Syntax extends Syntax