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Scala example source code file (ContravariantCoyonedaTest.scala)

This example Scala source code file (ContravariantCoyonedaTest.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

anyval, arbitrary, bigint, contravariantcoyoneda, contravariantcoyonedagens, contravariantcoyonedatest, ctcoorder, list, schwartzian, schwartzian\-transformed, speclite

The ContravariantCoyonedaTest.scala Scala example source code

package scalaz

import org.scalacheck._
import org.scalacheck.Prop.forAll

import std.anyVal._
import std.list._
import std.string._
import std.tuple._

object ContravariantCoyonedaGens {
  val CtCoOrder = ContravariantCoyoneda.by[Order]
  type CtCoOrder[A] = ContravariantCoyoneda[Order, A]

  final class Schwartzian[F[_], A, FA <: ContravariantCoyoneda[F, A]](val self: FA) /*extends AnyVal*/ {
    import self._
    @inline def schwartzianPre: A => (I, A) = a => (k(a), a)
    @inline def schwartzianPost: ((I, A)) => A = _._2
    @inline def schwartzianOrder(implicit F: Contravariant[F])
        : F[(I, A)] = F.contramap(fi)(_._1)
  }

  @inline implicit def Schwartzian[F[_], A](co: ContravariantCoyoneda[F, A])
      : Schwartzian[F, A, co.type] = new Schwartzian[F, A, co.type](co)

  def cmappedOrderLaws[A: Arbitrary](co: CtCoOrder[A]) = {
    implicit val ran = co.run
    scalaz.scalacheck.ScalazProperties.order.laws[A]
  }

  def aToString[A] = CtCoOrder((_:A).toString)

  val evensFirst = CtCoOrder{x:Int =>
    if (x % 2 == 0) (0, x)
    else (1, x)
  }

  val negated = CtCoOrder{x:Int => -x}

  val probablePrime = CtCoOrder{x:Int =>
    ((x - 1 : BigInt) isProbablePrime 5, x)
  }

  val intOrders: Gen[CtCoOrder[Int]] =
    Gen.oneOf[CtCoOrder[Int]](
      aToString[Int], evensFirst, negated, probablePrime)
}

object ContravariantCoyonedaTest extends SpecLite {
  import ContravariantCoyonedaGens._

  implicit val arbIntOrders = Arbitrary(intOrders)

  checkAll(cmappedOrderLaws(aToString[Int]))
  checkAll(cmappedOrderLaws(evensFirst))
  checkAll(cmappedOrderLaws(negated))
  checkAll(cmappedOrderLaws(probablePrime))

  "contravariant identity law" ! forAll {(xs: List[Int]) =>
    val co = CtCoOrder(identity[Int])
    xs.sorted(co.run.toScalaOrdering) must_=== xs.sorted
  }

  "Schwartzian-transformed sort equals normal sort" ! forAll{
    (xs: List[Int], o: CtCoOrder[Int]) =>
    xs.map(o.schwartzianPre)
      .sorted(o.schwartzianOrder.toScalaOrdering)
      .map(o.schwartzianPost) must_=== xs.sorted(o.run.toScalaOrdering)
  }
}

Other Scala examples (source code examples)

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



my book on functional programming

 

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