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Scala example source code file (EnumerateeT.scala)

This example Scala source code file (EnumerateeT.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

applicative, enumerateet, enumeratort, input, iterateet, long, monad, stepel, stept

The EnumerateeT.scala Scala example source code

package scalaz
package iteratee

import Iteratee._
import Ordering._

trait EnumerateeT[O, I, F[_]] { self =>
  def apply[A]: StepT[I, F, A] => IterateeT[O, F, StepT[I, F, A]]

  def run(enum: EnumeratorT[O, F])(implicit M: Monad[F]): EnumeratorT[I, F] = {
    new EnumeratorT[I, F] {
      def apply[A] = (s: StepT[I, F, A]) => iterateeT((self[A](s) &= enum).run)
    }
  }
}

object EnumerateeT extends EnumerateeTFunctions

trait EnumerateeTFunctions {
  /**
   * Applies a function to each input element and feeds the resulting outputs to the inner iteratee.
   */
  def map[O, I, F[_] : Monad](f: O => I): EnumerateeT[O, I, F] =
    new EnumerateeT[O, I, F] {
      def apply[A] = {
        def loop = step andThen cont[O, F, StepT[I, F, A]]
        def step: (Input[I] => IterateeT[I, F, A]) => (Input[O] => IterateeT[O, F, StepT[I, F, A]]) = {
          k => in =>
            in(
              el = e => k(elInput(f(e))) >>== doneOr(loop)
              , empty = cont(step(k))
              , eof = done(scont(k), in)
            )
        }

        doneOr(loop)
      }
    }

  def flatMap[O, I, F[_]: Monad](f: O => EnumeratorT[I, F]): EnumerateeT[O, I, F] =
    new EnumerateeT[O, I, F] {
      def apply[A] = {
        def loop(step: StepT[I, F, A]): IterateeT[O, F, StepT[I, F, A]] = {
          step.fold(
            cont = contf => cont[O, F, StepT[I, F, A]] {
              (_: Input[O]).map(e => f(e)).fold(
                el    = en => en.apply(step) >>== loop,
                empty = contf(emptyInput) >>== loop,
                eof   = done(step, emptyInput)
              )
            },
            done = (a, _) => done(sdone(a, emptyInput), emptyInput)
          )
        }

        loop
      }
    }

  def collect[O, I, F[_] : Monad](pf: PartialFunction[O, I]): EnumerateeT[O, I, F] =
    new EnumerateeT[O, I, F] {
      def apply[A] = {
        def loop = step andThen cont[O, F, StepT[I, F, A]]
        def step: (Input[I] => IterateeT[I, F, A]) => (Input[O] => IterateeT[O, F, StepT[I, F, A]]) = {
          k => in =>
            in(
              el = e => if (pf.isDefinedAt(e)) k(elInput(pf(e))) >>== doneOr(loop) else cont(step(k))
              , empty = cont(step(k))
              , eof = done(scont(k), in)
            )
        }

        doneOr(loop)
      }
    }

  def filter[E, F[_] : Monad](p: E => Boolean): EnumerateeT[E, E, F] =
    new EnumerateeT[E, E, F] {
      def apply[A] = {
        def loop = step andThen cont[E, F, StepT[E, F, A]]
        def step: (Input[E] => IterateeT[E, F, A]) => (Input[E] => IterateeT[E, F, StepT[E, F, A]]) = {
          k => in =>
            in(
              el = e =>
                if (p(e)) k(in) >>== doneOr(loop)
                else cont(step(k))
              , empty = cont(step(k))
              , eof = done(scont(k), in)
            )
        }

        doneOr(loop)
      }
    }

  /**
   * Uniqueness filter. Assumes that the input enumerator is already sorted.
   */
  def uniq[E: Order, F[_]: Monad]: EnumerateeT[E, E, F] =
    new EnumerateeT[E, E, F] {
      def apply[A] = {
        def step(s: StepT[E, F, A], last: Input[E]): IterateeT[E, F, A] =
          s mapCont { k =>
            cont { in =>
              val inr = in.filter(e => last.forall(l => Order[E].order(e, l) != EQ))
              k(inr) >>== (step(_, in))
            }
          }

        s => step(s, emptyInput).map(sdone(_, emptyInput))
      }
    }

  /**
   * Zips with the count of elements that have been encountered.
   */
  def zipWithIndex[E, F[_]: Monad]: EnumerateeT[E, (E, Long), F] =
    new EnumerateeT[E, (E, Long), F] {
      def apply[A] = {
        type StepEl = Input[(E, Long)] => IterateeT[(E, Long), F, A]
        def loop(i: Long) = (step(_: StepEl, i)) andThen (cont[E, F, StepT[(E, Long), F, A]])
        def step(k: StepEl, i: Long): (Input[E] => IterateeT[E, F, StepT[(E, Long), F, A]]) = {
          (in: Input[E]) =>
            in.map(e => (e, i)).fold(
              el = e => k(elInput(e)) >>== doneOr(loop(i + 1))
              , empty = cont(step(k, i))
              , eof = done(scont(k), in)
            )
        }

        doneOr(loop(0))
      }
    }

  def group[E, F[_], G[_]](n: Int)(implicit F: Applicative[F], FE: Monoid[F[E]], G: Monad[G]): EnumerateeT[E, F[E], G] =
    new EnumerateeT[E, F[E], G] {
      def apply[A] = take[E, F](n).up[G].sequenceI.apply[A]
    }

  def splitOn[E, F[_], G[_]](p: E => Boolean)(implicit F: Applicative[F], FE: Monoid[F[E]], G: Monad[G]): EnumerateeT[E, F[E], G] =
    new EnumerateeT[E, F[E], G] {
      def apply[A] = {
        (takeWhile[E, F](p).up[G] flatMap (xs => drop[E, G](1).map(_ => xs))).sequenceI.apply[A]
      }
    }

  def cross[E1, E2, F[_]: Monad](e2: EnumeratorT[E2, F]): EnumerateeT[E1, (E1, E2), F] =
    new EnumerateeT[E1, (E1, E2), F] {
      def apply[A] = {
        def outerLoop(step: StepT[(E1, E2), F, A]): IterateeT[E1, F, StepT[(E1, E2), F, A]] =
          for {
            outerOpt   <- head[E1, F]
            sa         <- outerOpt match {
                            case Some(e) =>
                              val pairingIteratee = EnumerateeT.map[E2, (E1, E2), F]((a: E2) => (e, a)).apply(step)
                              val nextStep = (pairingIteratee &= e2).run
                              iterateeT[(E1, E2), F, A](nextStep) >>== outerLoop

                            case None    =>
                              done[E1, F, StepT[(E1, E2), F, A]](step, eofInput)
                          }
          } yield sa

        outerLoop
      }
    }


  def doneOr[O, I, F[_] : Applicative, A](f: (Input[I] => IterateeT[I, F, A]) => IterateeT[O, F, StepT[I, F, A]]): StepT[I, F, A] => IterateeT[O, F, StepT[I, F, A]] = {
    (s: StepT[I, F, A]) => s.mapContOr(k => f(k), done(s, emptyInput))
  }
}

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