Scala example source code file (WriterTTest.scala)

This example Scala source code file (WriterTTest.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, bind, functor, int, monad, monadplus, monoid, plusempty, semigroup, traverse

The WriterTTest.scala Scala example source code

package scalaz

import scalaz.scalacheck.ScalazProperties._
import scalaz.scalacheck.ScalazArbitrary._
import scalaz.scalacheck.ScalaCheckBinding._
import std.AllInstances._
import org.scalacheck.Arbitrary
import Id._
import org.scalacheck.Prop.forAll

object WriterTTest extends SpecLite {

  type WriterTOpt[W, A] = WriterT[Option, W, A]
  type WriterTOptInt[A] = WriterTOpt[Int, A]
  type IntOr[A] = Int \/ A
  type WriterTEither[A] = WriterT[IntOr, Int, A]

  checkAll(equal.laws[WriterTOptInt[Int]])
  checkAll(monoid.laws[WriterTOptInt[Int]])
  checkAll(monadError.laws[WriterTEither, Int])
  checkAll(traverse.laws[WriterTOptInt])
  checkAll(bindRec.laws[WriterTOptInt])
  checkAll(monadPlus.strongLaws[WriterTOptInt])
  checkAll(bifunctor.laws[WriterTOpt])
  checkAll(functor.laws[WriterT[NonEmptyList, Int, ?]])
  checkAll(bitraverse.laws[WriterTOpt])

  implicit def writerArb[W, A](implicit W: Arbitrary[W], A: Arbitrary[A]): Arbitrary[Writer[W, A]] =
    Applicative[Arbitrary].apply2(W, A)((w, a) => Writer[W, A](w, a))

  checkAll(comonad.laws[Writer[Int, ?]])

  "flatMapF consistent with flatMap" ! forAll {
    (fa: WriterTOptInt[Int], f: Int => Option[(Int, Int)]) =>
      fa.flatMapF(f) must_=== fa.flatMap(f andThen WriterT.writerT)
  }

  private def writerTUcompilationTest: Unit = {
    import syntax.either._
    val a: String \/ (Int, Boolean) = (1, true).right[String]
    WriterT.writerTU(a)
  }

  object instances {
    def plus[F[_]: Plus, W] = Plus[WriterT[F, W, ?]]
    def plusEmpty[F[_]: PlusEmpty, W] = PlusEmpty[WriterT[F, W, ?]]
    def functor[F[_]: Functor, W] = Functor[WriterT[F, W, ?]]
    def apply[F[_]: Apply, W: Semigroup] = Apply[WriterT[F, W, ?]]
    def applicative[F[_]: Applicative, W: Monoid] = Applicative[WriterT[F, W, ?]]
    def bind[F[_]: Bind, W: Semigroup] = Bind[WriterT[F, W, ?]]
    def bindRec[F[_]: BindRec: Applicative, W: Semigroup] = BindRec[WriterT[F, W, ?]]
    def monad[F[_]: Monad, W: Monoid] = Monad[WriterT[F, W, ?]]
    def monadPlus[F[_]: MonadPlus, W: Monoid] = MonadPlus[WriterT[F, W, ?]]
    def monadError[F[_], W: Monoid, E](implicit F: MonadError[F, E]) = MonadError[WriterT[F, W, ?], E]
    def foldable[F[_]: Foldable, W] = Foldable[WriterT[F, W, ?]]
    def traverse[F[_]: Traverse, W] = Traverse[WriterT[F, W, ?]]

    // checking absence of ambiguity
    def plus[F[_]: PlusEmpty, W] = Plus[WriterT[F, W, ?]]
    def plus[F[_]: MonadPlus, W] = Plus[WriterT[F, W, ?]]
    def plusEmpty[F[_]: MonadPlus, W] = PlusEmpty[WriterT[F, W, ?]]
    def functor[F[_]: Monad, W: Monoid] = Functor[WriterT[F, W, ?]]
    def functor[F[_]: MonadPlus, W: Monoid] = Functor[WriterT[F, W, ?]]
    def apply[F[_]: MonadPlus, W: Monoid] = Apply[WriterT[F, W, ?]]
    def apply[F[_]: Monad, W: Monoid] = Apply[WriterT[F, W, ?]]
    def apply[F[_]: Monad, W: Semigroup] = Apply[WriterT[F, W, ?]]
    def apply[F[_]: Bind, W: Monoid] = Apply[WriterT[F, W, ?]]
    def apply[F[_]: Bind, W: Semigroup] = Apply[WriterT[F, W, ?]]
    def apply[F[_]: Apply, W: Monoid] = Apply[WriterT[F, W, ?]]
    def applicative[F[_]: Monad, W: Monoid] = Applicative[WriterT[F, W, ?]]
    def applicative[F[_]: MonadPlus, W: Monoid] = Applicative[WriterT[F, W, ?]]
    def bind[F[_]: MonadPlus, W: Monoid] = Bind[WriterT[F, W, ?]]
    def bind[F[_]: Monad, W: Monoid] = Bind[WriterT[F, W, ?]]
    def bind[F[_]: Monad, W: Semigroup] = Bind[WriterT[F, W, ?]]
    def bind[F[_]: Bind, W: Monoid] = Bind[WriterT[F, W, ?]]
    def monad[F[_]: MonadPlus, W: Monoid] = Monad[WriterT[F, W, ?]]
    def functor[F[_]: Traverse, W: Monoid] = Functor[WriterT[F, W, ?]]
    def foldable[F[_]: Traverse, W] = Foldable[WriterT[F, W, ?]]

    object writer {
      def functor[W] = Functor[Writer[W, ?]]
      def apply[W: Semigroup] = Apply[Writer[W, ?]]
      def applicative[W: Monoid] = Applicative[Writer[W, ?]]
      def bind[W: Semigroup] = Bind[Writer[W, ?]]
      def monad[W: Monoid] = Monad[Writer[W, ?]]
      def foldable[W] = Foldable[Writer[W, ?]](WriterT.writerTFoldable[Id, W])
      def traverse[W] = Traverse[Writer[W, ?]]
      def comonad[W] = Comonad[Writer[W, ?]]
    }
  }
}