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Scala example source code file (Const.scala)

This example Scala source code file (Const.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, const, constapply, consttraverse, equal, function0, monoid, order, semigroup

The Const.scala Scala example source code

package scalaz

final case class Const[A, B](getConst: A)

private sealed trait ConstSemigroup[A, B] extends Semigroup[Const[A, B]] {
  def A: Semigroup[A]

  override def append(f1: Const[A, B], f2: => Const[A, B]): Const[A, B] =
    Const(A.append(f1.getConst, f2.getConst))
}

private sealed trait ConstMonoid[A, B] extends Monoid[Const[A, B]] with ConstSemigroup[A, B] {
  def A: Monoid[A]

  override def zero: Const[A, B] =
    Const(A.zero)
}

private sealed trait ConstTraverse[C] extends Traverse[Const[C, ?]] {
  override def map[A, B](fa: Const[C, A])(f: A => B): Const[C, B] = Const(fa.getConst)

  override def traverseImpl[G[_], A, B](fa: Const[C, A])(f: A => G[B])(implicit G: Applicative[G]) =
    G.point(Const(fa.getConst))
}

private sealed trait ConstApply[C] extends Apply[Const[C, ?]] with ConstTraverse[C] {
  def C: Semigroup[C]

  override def ap[A, B](fa: => Const[C, A])(f: => Const[C, A => B]): Const[C, B] =
    Const(C.append(f.getConst, fa.getConst))
}

private sealed trait ConstApplicative[C] extends Applicative[Const[C, ?]] with ConstApply[C] {
  def C: Monoid[C]

  override def point[A](a: => A): Const[C, A] = Const(C.zero)
}

private sealed trait ConstEqual[A, B] extends Equal[Const[A, B]] {
  def OA: Equal[A]

  override def equal(a1: Const[A, B], a2: Const[A, B]): Boolean =
    OA.equal(a1.getConst, a2.getConst)

  override def equalIsNatural = OA.equalIsNatural
}

private sealed trait ConstOrder[A, B] extends Order[Const[A, B]] with ConstEqual[A, B] {
  def OA: Order[A]

  override def order(a1: Const[A, B], a2: Const[A, B]): Ordering =
    OA.order(a1.getConst, a2.getConst)
}

private class ConstContravariant[C] extends Contravariant[Const[C, ?]] {
  def contramap[A, B](r: Const[C, A])(f: B => A) =
    Const(r.getConst)
}

sealed abstract class ConstInstances1 {
  implicit def constTraverse[C]: Traverse[Const[C, ?]] =
    new ConstTraverse[C] {}

  implicit def constContravariant[C]: Contravariant[Const[C, ?]] =
    new ConstContravariant[C]
}

sealed abstract class ConstInstances0 extends ConstInstances1 {
  implicit def constEqual[A : Equal, B]: Equal[Const[A, B]] =
    new ConstEqual[A, B] {
      val OA: Equal[A] = implicitly
    }

  implicit def constSemigroup[A: Semigroup, B]: Semigroup[Const[A, B]] =
    new ConstSemigroup[A, B] {
      val A: Semigroup[A] = implicitly
    }

  implicit def constApply[C: Semigroup]: Apply[Const[C, ?]] =
    new ConstApply[C] {
      val C: Semigroup[C] = implicitly
    }
}

sealed abstract class ConstInstances extends ConstInstances0 {
  implicit def constOrder[A : Order, B]: Order[Const[A, B]] =
    new ConstOrder[A, B]{
      val OA: Order[A] = implicitly
    }

  implicit def constMonoid[A: Monoid, B]: Monoid[Const[A, B]] =
    new ConstMonoid[A, B] {
      val A: Monoid[A] = implicitly
    }

  implicit def constApplicative[C: Monoid]: Applicative[Const[C, ?]] =
    new ConstApplicative[C] {
      val C: Monoid[C] = implicitly
    }
}

object Const extends ConstInstances {

  /** A properly universally quantified constant function. */
  def const[A](a: A): Function0 ~> λ[α => A] =
    new (Function0 ~> λ[α => A]) {
      override def apply[B](fa: Function0[B]): A = a
    }
}

Other Scala examples (source code examples)

Here is a short list of links related to this Scala Const.scala source code file:



my book on functional programming

 

new blog posts

 

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