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Scala example source code file (Enumeratee2T.scala)

This example Scala source code file (Enumeratee2T.scala) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Scala by Example" TM.

Learn more about this Scala project at its project page.

Java - Scala tags/keywords

enumeratee2t, iterateem, iterateet, monad, option, some, stepm, stept

The Enumeratee2T.scala Scala example source code

package scalaz
package iteratee

import Iteratee._
import Ordering.{EQ, GT, LT}

trait Enumeratee2T[J, K, I, F[_]] {
  type IterateeM[α] = IterateeT[K, F, α]
  type StepM[α] = StepT[I, F, α]
  type InputI = Input[I]

  def apply[A]: StepM[A] => IterateeT[J, IterateeM, StepM[A]]
}

trait Enumeratee2TFunctions {
  import scalaz.syntax.order._

  @inline private def lift[J, K, F[_]: Monad, A](iter: IterateeT[K, F, A]): IterateeT[J, IterateeT[K, F, ?], A] =
    IterateeT.IterateeTMonadTrans[J].liftM[IterateeT[K, F, ?], A](iter)

  def cogroupI[J, K, F[_]](implicit M: Monad[F], order: (J, K) => Ordering): Enumeratee2T[J, K, Either3[J, (J, K), K], F] =
    new Enumeratee2T[J, K, Either3[J, (J, K), K], F] {
      def apply[A] = {
        // Used to 'replay' values from the right for when values from the left order equal
        // in the pathological case, this degrades to the cartesian product, which will blow up
        // your memory. Sorry!
        def advance(j: J, buf: List[K], s: StepT[Either3[J, (J, K), K], F, A]): IterateeT[Either3[J,(J, K),K],F,A] = {
          s mapCont { contf =>
            buf match {
              case k :: Nil if order(j, k) == EQ => contf(elInput(Middle3((j, k))))
              case k :: ks  if order(j, k) == EQ => contf(elInput(Middle3((j, k)))) >>== (advance(j, ks, _))
              case _ => contf(elInput(Left3(j)))
            }
          }
        }

        def step(s: StepM[A], rbuf: List[K]): IterateeT[J, IterateeM, StepM[A]] = {
          s.fold[IterateeT[J, IterateeM, StepM[A]]](
            cont = contf => {
              for {
                leftOpt  <- peek[J, IterateeM]
                rightOpt <- lift[J, K, F, Option[K]](peek[K, F])
                a <- (leftOpt, rightOpt) match {
                  case (left, Some(right)) if left.forall(order(_, right) == GT) =>
                    for {
                      _ <- lift[J, K, F, Option[K]](head[K, F])
                      a <- iterateeT[J, IterateeM, StepM[A]](contf(elInput(Right3(right))) >>== (step(_, Nil).value))
                    } yield a

                  case (Some(left), right) if right.forall(order(left, _) == LT) =>
                    for {
                      _ <- head[J, IterateeM]
                      a <- iterateeT[J, IterateeM, StepM[A]](advance(left, rbuf, scont(contf)) >>== (step(_, rbuf).value))
                    } yield a

                  case (Some(left), Some(right)) =>
                    for {
                      _ <- lift[J, K, F, Option[K]](head[K, F])
                      a <- step(s, if (rbuf.headOption.exists(order(left, _) == EQ)) right :: rbuf else right :: Nil)
                    } yield a

                  case _ => done[J, IterateeM, StepM[A]](s, eofInput)
                }
              } yield a
            },
            done = (a, r) => done[J, IterateeM, StepM[A]](sdone(a, if (r.isEof) eofInput else emptyInput), if (r.isEof) eofInput else emptyInput)
          )
        }

        step(_, Nil)
      }
    }

  def joinI[J, K, F[_]](implicit M: Monad[F], ord: (J, K) => Ordering): Enumeratee2T[J, K, (J, K), F] =
    new Enumeratee2T[J, K, (J, K), F] {
      def apply[A] = {
        def cstep(step: StepT[(J, K), F, A]): StepT[Either3[J, (J, K), K], F, StepT[(J, K), F, A]] = step.fold(
          cont = contf => scont { in: Input[Either3[J, (J, K), K]] =>
            val nextInput = in.flatMap(_.middleOr(emptyInput[(J, K)]) { elInput(_) })

            contf(nextInput) >>== (s => cstep(s).pointI)
          },
          done = (a, r) => sdone(sdone(a, if (r.isEof) eofInput else emptyInput), if (r.isEof) eofInput else emptyInput)
        )

        (step: StepT[(J, K), F, A]) => cogroupI[J, K, F].apply(cstep(step)) flatMap { endStep[J, K, (J, K), F, A] }
      }
    }

  def mergeI[E: Order, F[_]: Monad]: Enumeratee2T[E, E, E, F] =
    new Enumeratee2T[E, E, E, F] {
      def apply[A] = {
        def step(s: StepM[A]): IterateeT[E, IterateeM, StepM[A]] =
          s.fold[IterateeT[E, IterateeM, StepM[A]]](
            cont = contf => {
              for {
                leftOpt  <- peek[E, IterateeM]
                rightOpt <- lift[E, E, F, Option[E]](peek[E, F])
                a <- (leftOpt, rightOpt) match {
                  case (left, Some(right)) if left.forall(_ > right) =>
                    for {
                      _ <- lift[E, E, F, Option[E]](head[E, F])
                      a <- iterateeT[E, IterateeM, StepM[A]](contf(elInput(right)) >>== (step(_).value))
                    } yield a

                  case (Some(left), _) =>
                    for {
                      _ <- head[E, IterateeM]
                      a <- iterateeT[E, IterateeM, StepM[A]](contf(elInput(left)) >>== (step(_).value))
                    } yield a

                  case _ => done[E, IterateeM, StepM[A]](s, eofInput)
                }
              } yield a
            },
            done = (a, r) => done[E, IterateeM, StepM[A]](sdone(a, if (r.isEof) eofInput else emptyInput), if (r.isEof) eofInput else emptyInput)
          )

        step
      }
    }

  def parFoldI[J, K, F[_]](f: K => J)(implicit order: (J, K) => Ordering, m: Monoid[J], M: Monad[F]): Enumeratee2T[J, K, J, F] =
    new Enumeratee2T[J, K, J, F] {
      def apply[A] = {
        def cstep(step: StepT[J, F, A]): StepT[Either3[J, (J, K), K], F, StepT[J, F, A]]  = step.fold(
          cont = contf => scont { in: Input[Either3[J, (J, K), K]] =>
            val nextInput = in map {
              case Left3(j) => j
              case Middle3((j, k)) => m.append(j, f(k))
              case Right3(k) => m.zero
            }

            contf(nextInput) >>== (s => cstep(s).pointI)
          },
          done = (a, r) => sdone(sdone(a, if (r.isEof) eofInput else emptyInput), if (r.isEof) eofInput else emptyInput)
        )

        (step: StepT[J, F, A]) => cogroupI[J, K, F].apply(cstep(step)) flatMap { endStep[J, K, J, F, A] }
      }
    }

  private def endStep[J, K, EE, F[_]: Monad, A](sa: StepT[Either3[J, (J, K), K], F, StepT[EE, F, A]]) = {
    IterateeT.IterateeTMonadTransT[J, λ[(β[_], α) => IterateeT[K, β, α]]].liftM(sa.pointI.run)
  }
}

object Enumeratee2T extends Enumeratee2TFunctions

// vim: set ts=4 sw=4 et:

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