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Scala example source code file (ApplicativeTest.scala)

This example Scala source code file (ApplicativeTest.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

applicativetest, int, list, monad, nil, none, option, some, speclite

The ApplicativeTest.scala Scala example source code

package scalaz

import org.scalacheck.Gen
import org.scalacheck.Prop.forAll

object ApplicativeTest extends SpecLite {

  // In c44c206461fe, the functions `replicateM`, `replicateM_`, `filterM`
  // and `partitionM` have been generalized from `Monad` to `Applicative`.
  // We compare the old with the new implementation here.

  import std.list._
  import std.option._
  import std.anyVal._
  import syntax.std.list._
  import syntax.applicative._

  def replicateM[F[_] : Monad, A](n: Int, fa: F[A]): F[List[A]] =
    listInstance.sequence(List.fill(n)(fa))

  def filterM[F[_] : Monad, A](l: List[A], f: A => F[Boolean]): F[List[A]] =
    l match {
      case Nil => Monad[F].point(List())
      case h :: t => Monad[F].bind(f(h))(b => Monad[F].map(filterM(t, f))(t => if (b) h :: t else t))
    }

  "replicateM is the same" ! forAll { (fa: Option[Int]) => forAll(Gen.choose(0, 100)) { n =>
    fa.replicateM(n) must_===(replicateM(n, fa))
  }}

  "filterM is the same" ! forAll { (l: List[Int]) =>
    // don't make `None` too likely
    def pred(n: Int) = if (n < 0 && n % 2 == 0) None else Some(n % 2 == 0)
    l.filterM(pred) must_===(filterM(l, pred))
  }

}

// vim: expandtab:ts=2:sw=2

Other Scala examples (source code examples)

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



my book on functional programming

 

new blog posts

 

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