Scala example source code file (CoKleisliTest.scala)

This example Scala source code file (CoKleisliTest.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

arbitrary, arrow, cobind, cokleisli, comonad, compose, gen, int, nonemptylist, option, profunctor

The CoKleisliTest.scala Scala example source code

package scalaz

import scalaz.scalacheck.ScalazProperties._
import org.scalacheck.{Arbitrary, Gen}
import scalaz.std.option._

object CokleisliTest extends SpecLite {

  implicit val cokleisliArb1: Arbitrary[Cokleisli[Option, Int, Int]] = {
    def arb(f: (Option[Int], Int, Int) => Int): Gen[Cokleisli[Option, Int, Int]] =
      for{
        a <- implicitly[Arbitrary[Int]].arbitrary
        b <- implicitly[Arbitrary[Int]].arbitrary
      } yield Cokleisli[Option, Int, Int](f(_, a, b))

    Arbitrary(Gen.oneOf(
      arb((_, n, _) => n),
      arb((a, b, c) => a getOrElse b),
      arb((a, b, c) => a.map(_ + b) getOrElse c),
      arb((a, b, c) => a.map(_ - b) getOrElse c)
    ))
  }


  implicit val cokleisliArb2: Arbitrary[Cokleisli[Option, Int, Int => Int]] = {
    def arb(f: (Option[Int], Int) => (Int => Int)): Gen[Cokleisli[Option, Int, Int => Int]] =
      implicitly[Arbitrary[Int]].arbitrary.map(a => Cokleisli[Option, Int, Int => Int](f(_, a)))

    Arbitrary(Gen.oneOf(
      arb((_, n) => Function.const(n)),
      arb((_, _) => x => x),
      arb((_, n) => _ + n),
      arb((_, n) => _ - n),
      arb((a, b) => a.map(_ + b) getOrElse _),
      arb((a, b) => a.map(_ - b) getOrElse _)
    ))
  }

  implicit val cokleisliEqual: Equal[Cokleisli[Option, Int, Int]] =
    Equal.equal{ (a, b) =>
      a(None) == b(None) && Iterator.fill(20)(util.Random.nextInt).map(Option(_)).forall(n => a(n) == b(n))
    }

  checkAll(bindRec.laws[Cokleisli[Option, Int, ?]])
  checkAll(bind.laws[Cokleisli[Option, Int, ?]])
  checkAll(profunctor.laws[Cokleisli[Option, ?, ?]])

  "compose" in {
    import std.AllInstances._

    val ck = Cokleisli((a: NonEmptyList[Int]) => a.size)
    val ck1 = ck compose ck
    val run: Int = ck1.run(NonEmptyList(0, 0))
    run must_===(2)
  }

  object instances {
    def bindRec[F[_], W] = BindRec[Cokleisli[F, W, ?]]
    def monad[F[_], W] = Monad[Cokleisli[F, W, ?]]
    def compose[F[_]](implicit F: Cobind[F]) = Compose[Cokleisli[F, ?, ?]]
    def profunctor[F[_]: Functor] = Profunctor[Cokleisli[F, ?, ?]]
    def arrow[F[_] : Comonad] = Arrow[Cokleisli[F, ?, ?]]
    def prochoice[F[_] : Comonad] = ProChoice[Cokleisli[F, ?, ?]]

    // checking absence of ambiguity
    def compose[F[_]](implicit F: Comonad[F]) = Compose[Cokleisli[F, ?, ?]]
    def profunctor[F[_]: Comonad] = Profunctor[Cokleisli[F, ?, ?]]
  }
}