Scala example source code file (ListTTest.scala)

This example Scala source code file (ListTTest.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

functor, int, list, listt, listtopt, listttest, monad, monoid, option, semigroup, speclite

The ListTTest.scala Scala example source code

package scalaz

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

object ListTTest extends SpecLite {
  type ListTOpt[A] = ListT[Option, A]

  "fromList / toList" ! forAll {
    (ass: List[List[Int]]) =>
      ListT.fromList(ass).toList must_===(ass)
  }

  "filter all" ! forAll {
    (ass: ListT[List, Int]) =>
      ass.filter(_ => true) must_===(ass)
  }

  "filter none" ! forAll {
    (ass: ListT[List, Int]) =>
      val filtered = ass.filter(_ => false)
      val isEmpty = filtered.isEmpty
      isEmpty.toList.forall(identity)
  }

  "find" ! forAll {
    (ass: ListTOpt[Int]) =>
      ass.find(_ > 0 ) must_===(OptionT.optionT(ass.run.map(_.find( _ > 0))))
  }

  "drop" ! forAll {
    (ass: Option[List[Int]], x: Int) =>
      ListT.fromList(ass).drop(x).toList must_===(ass.map(_.drop(x)))
  }

  "take" ! forAll {
    (ass: Option[List[Int]], x: Int) =>
      ListT.fromList(ass).take(x).toList must_===(ass.map(_.take(x)))
  }

  "map" ! forAll {
    (ass: List[List[Int]]) =>
      ListT.fromList(ass).map(_ * 2).toList must_===(ass.map(_.map(_ * 2)))
  }

  "flatMap" ! forAll {
    (ass: List[List[Int]]) =>
      (ListT.fromList(ass).flatMap(number => ListT.fromList(List(List(number.toFloat)))).toList
      must_===(ass.map(_.flatMap(number => List(number.toFloat)))))
  }

  // Exists to ensure that fromList and map don't stack overflow.
  "large map" ! {
    val list = (0 to 400).toList.map(_ => (0 to 400).toList)
    ListT.fromList(list).map(_ * 2).toList must_===(list.map(_.map(_ * 2)))
    ()
  }

  "listT" ! forAll {
    (ass: Option[List[Int]]) =>
      ListT.listT(ass).run == ass
  }

  checkAll(equal.laws[ListTOpt[Int]])
  checkAll(monoid.laws[ListTOpt[Int]])
  checkAll(plusEmpty.laws[ListTOpt])
  checkAll(monad.laws[ListTOpt])
  checkAll(monadPlus.laws[ListTOpt])

  object instances {
    def semigroup[F[_]: Monad, A] = Semigroup[ListT[F, A]]
    def monoid[F[_]: Monad, A] = Monoid[ListT[F, A]]
    def monad[F[_]: Monad] = Monad[ListT[F, ?]]
    def functor[F[_]: Functor] = Functor[ListT[F, ?]]

    // checking absence of ambiguity
    def functor[F[_]: Monad] = Functor[ListT[F, ?]]
  }
}