Scala example source code file (IdT.scala)

This example Scala source code file (IdT.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, apply, functor, idt, monad, traverse

The IdT.scala Scala example source code

package scalaz

final case class IdT[F[_], A](run: F[A]) {
  def map[B](f: A => B)(implicit F: Functor[F]) =
    new IdT[F, B](F.map(run)(f))

  def flatMap[B](f: A => IdT[F, B])(implicit F: Bind[F]) =
    new IdT[F, B](F.bind(run)(f andThen ((_: IdT[F, B]).run)))

  def flatMapF[B](f: A => F[B])(implicit F: Bind[F]) =
    new IdT[F, B](F.bind(run)(f))

  def foldRight[Z](z: => Z)(f: (A, => Z) => Z)(implicit F: Foldable[F]): Z =
    F.foldRight[A, Z](run, z)(f)

  def traverse[G[_], B](f: A => G[B])(implicit F: Traverse[F], G: Applicative[G]): G[IdT[F, B]] =
    G.map(F.traverse(run)(f))(IdT(_))

  def ap[B](f: => IdT[F, A => B])(implicit F: Apply[F]) =
    new IdT(F.ap(run)(f.run))
}

sealed abstract class IdTInstances4 {
  implicit def idTFunctor[F[_]](implicit F0: Functor[F]): Functor[IdT[F, ?]] =
    new IdTFunctor[F] {
      implicit def F: Functor[F] = F0
    }
}

sealed abstract class IdTInstances3 extends IdTInstances4 {
  implicit def idTApply[F[_]](implicit F0: Apply[F]): Apply[IdT[F, ?]] =
    new IdTApply[F] {
      implicit def F: Apply[F] = F0
    }
}

sealed abstract class IdTInstances2 extends IdTInstances3 {
  implicit def idTApplicative[F[_]](implicit F0: Applicative[F]): Applicative[IdT[F, ?]] =
    new IdTApplicative[F] {
      implicit def F: Applicative[F] = F0
    }
}

sealed abstract class IdTInstances1 extends IdTInstances2 {
  implicit def idTFoldable[F[_]](implicit F0: Foldable[F]): Foldable[IdT[F, ?]] =
    new IdTFoldable[F] {
      implicit def F: Foldable[F] = F0
    }
  implicit def idTBindRec[F[_]](implicit F0: BindRec[F]): BindRec[IdT[F, ?]] =
    new IdTBindRec[F] {
      implicit def F: BindRec[F] = F0
    }
}

sealed abstract class IdTInstances0 extends IdTInstances1 {
  implicit def idTMonad[F[_]](implicit F0: Monad[F]): Monad[IdT[F, ?]] =
    new IdTMonad[F] {
      implicit def F: Monad[F] = F0
    }

  implicit def idTOrder[F[_], A](implicit F: Order[F[A]]): Order[IdT[F, A]] =
    F.contramap(_.run)
}

sealed abstract class IdTInstances extends IdTInstances0 {
  implicit val idTHoist: Hoist[IdT] = IdTHoist

  implicit def idTTraverse[F[_]](implicit F0: Traverse[F]): Traverse[IdT[F, ?]] =
    new IdTTraverse[F] {
      implicit def F: Traverse[F] = F0
    }

  implicit def idTEqual[F[_], A](implicit F: Equal[F[A]]): Equal[IdT[F, A]] =
    F.contramap(_.run)
}

object IdT extends IdTInstances

//
// Implementation traits for type class instances
//

private trait IdTFunctor[F[_]] extends Functor[IdT[F, ?]] {
  implicit def F: Functor[F]

  override def map[A, B](fa: IdT[F, A])(f: A => B) = fa map f
}

private trait IdTApply[F[_]] extends Apply[IdT[F, ?]] with IdTFunctor[F] {
  implicit def F: Apply[F]

  override def ap[A, B](fa: => IdT[F, A])(f: => IdT[F, A => B]): IdT[F, B] = fa ap f
}

private trait IdTApplicative[F[_]] extends Applicative[IdT[F, ?]] with IdTApply[F] {
  implicit def F: Applicative[F]

  def point[A](a: => A) = new IdT[F, A](F.point(a))
}

private trait IdTBind[F[_]] extends Bind[IdT[F, ?]] with IdTApply[F] {
  implicit def F: Bind[F]

  final def bind[A, B](fa: IdT[F, A])(f: A => IdT[F, B]) = fa flatMap f
}

private trait IdTBindRec[F[_]] extends BindRec[IdT[F, ?]] with IdTBind[F] {
  implicit def F: BindRec[F]

  final def tailrecM[A, B](f: A => IdT[F, A \/ B])(a: A): IdT[F, B] =
    IdT(F.tailrecM[A, B](a => F.map(f(a).run)(identity))(a))
}

private trait IdTMonad[F[_]] extends Monad[IdT[F, ?]] with IdTApplicative[F] with IdTBind[F] {
  implicit def F: Monad[F]
}

private trait IdTFoldable[F[_]] extends Foldable.FromFoldr[IdT[F, ?]] {
  implicit def F: Foldable[F]

  override def foldRight[A, B](fa: IdT[F, A], z: => B)(f: (A, => B) => B): B = fa.foldRight(z)(f)
}

private trait IdTTraverse[F[_]] extends Traverse[IdT[F, ?]] with IdTFoldable[F] with IdTFunctor[F]{
  implicit def F: Traverse[F]

  def traverseImpl[G[_] : Applicative, A, B](fa: IdT[F, A])(f: A => G[B]): G[IdT[F, B]] = fa traverse f
}

private object IdTHoist extends Hoist[IdT] {
  def liftM[G[_], A](a: G[A])(implicit G: Monad[G]): IdT[G, A] =
    new IdT[G, A](a)

  def hoist[M[_]: Monad, N[_]](f: M ~> N) =
    new (IdT[M, ?] ~> IdT[N, ?]) {
      def apply[A](fa: IdT[M, A]): IdT[N, A] =
        new IdT[N, A](f(fa.run))
    }

  implicit def apply[G[_] : Monad]: Monad[IdT[G, ?]] =
    IdT.idTMonad[G]
}

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