Scala example source code file (ReaderWriterStateTTest.scala)

This example Scala source code file (ReaderWriterStateTTest.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.

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Java - Scala tags/keywords

bind, functor, int, monad, monadplus, monoid, plusempty, some

The ReaderWriterStateTTest.scala Scala example source code

package scalaz

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

object ReaderWriterStateTTest extends SpecLite {
  type RWSOptInt[A] = RWST[Option, Int, Int, Int, A]
  implicit val RWSOptIntArb = Arbitrary(Gen.oneOf[RWSOptInt[Int]](
    Gen.const(RWST[Option, Int, Int, Int, Int]((r: Int, s: Int) => None)),
    Gen.const(RWST[Option, Int, Int, Int, Int]((r: Int, s: Int) => Some((0, 0, 0)))),
    Gen.const(RWST[Option, Int, Int, Int, Int]((r: Int, s: Int) => Some((r, r, r)))),
    Gen.const(RWST[Option, Int, Int, Int, Int]((r: Int, s: Int) => Some((s, s, s))))
  ))
  implicit val RWSOptIntIntArb = Arbitrary(Gen.oneOf[RWSOptInt[Int => Int]](
    Gen.const(RWST[Option, Int, Int, Int, Int => Int]((r: Int, s: Int) => None)),
    Gen.const(RWST[Option, Int, Int, Int, Int => Int]((r: Int, s: Int) => Some((0, x => 0, 0)))),
    Gen.const(RWST[Option, Int, Int, Int, Int => Int]((r: Int, s: Int) => Some((r, x => r, r)))),
    Gen.const(RWST[Option, Int, Int, Int, Int => Int]((r: Int, s: Int) => Some((s, x => s, s)))),
    Gen.const(RWST[Option, Int, Int, Int, Int => Int]((r: Int, s: Int) => Some((s, x => x, s))))
  ))

  implicit val RWSOptIntEqual = new Equal[RWSOptInt[Int]] {
    def equal(a1: RWSOptInt[Int], a2: RWSOptInt[Int]) = a1.run(0, 0) == a2.run(0, 0)
  }

  checkAll(bindRec.laws[RWSOptInt])
  checkAll(monadPlus.strongLaws[RWSOptInt])

  "ReaderWriterStateT can be trampolined without stack overflow" in {
    import scalaz.Free._
    val result = (0 to 10000).toList.map(ii => ReaderWriterStateT[Trampoline, Unit, String, Int, Int]((_, i: Int) => Trampoline.done(("", i, ii))))
      .foldLeft(ReaderWriterStateT[Trampoline, Unit, String, Int, Int]((_, i: Int) => Trampoline.done(("", i, i))))( (a, b) => a.flatMap(_ => b))
    10000 must_=== result.run((),0).run._3
  }

  object instances {
    def functor[F[_]: Functor, R, W, S] = Functor[RWST[F, R, W, S, ?]]
    def plus[F[_]: Plus, R, W, S1, S2] = Plus[IRWST[F, R, W, S1, S2, ?]]
    def plusEmpty[F[_]: PlusEmpty, R, W, S1, S2] = PlusEmpty[IRWST[F, R, W, S1, S2, ?]]
    def bindRec[F[_]: BindRec : Monad, R, W: Semigroup, S] = BindRec[RWST[F, R, W, S, ?]]
    def monad[F[_]: Monad, R, W: Monoid, S] = Monad[RWST[F, R, W, S, ?]]
    def monadPlus[F[_]: MonadPlus, R, W: Monoid, S] = MonadPlus[RWST[F, R, W, S, ?]]
    def bind[F[_]: Bind, R, W: Semigroup, S] = Bind[RWST[F, R, W, S, ?]]
    def monadReader[F[_]: Monad, R, W: Monoid, S] = MonadReader[RWST[F, R, W, S, ?], R]
    def monadState[F[_]: Monad, R, W: Monoid, S] = MonadState[RWST[F, R, W, S, ?], S]
    def monadTrans[R, W: Monoid, S] = MonadTrans[λ[(f[_], α) => RWST[f, R, W, S, α]]]
    // checking absence of ambiguity
    def functor[F[_]: Monad, R, W: Monoid, S] = Functor[RWST[F, R, W, S, ?]]
    def functor[F[_]: Bind, R, W: Semigroup, S] = Functor[RWST[F, R, W, S, ?]]
    def functor[F[_]: MonadPlus, R, W: Monoid, S] = Functor[RWST[F, R, W, S, ?]]
    def plus[F[_]: PlusEmpty, R, W, S] = Plus[RWST[F, R, W, S, ?]]
    def plus[F[_]: MonadPlus, R, W, S] = Plus[RWST[F, R, W, S, ?]]
    def plusEmpty[F[_]: MonadPlus, R, W, S] = PlusEmpty[RWST[F, R, W, S, ?]]
    def bind[F[_]: Monad, R, W: Monoid, S] = Bind[RWST[F, R, W, S, ?]]
    def bind[F[_]: MonadPlus, R, W: Monoid, S] = Bind[RWST[F, R, W, S, ?]]
    def monad[F[_]: MonadPlus, R, W: Monoid, S] = Monad[RWST[F, R, W, S, ?]]
  }
}