Scala example source code file (CheckEither.scala)

This example Scala source code file (CheckEither.scala) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Scala tags/keywords

arbitrary, either, either, int, int, left, left, none, right, right, seq, some, string, test

The Scala CheckEither.scala source code

import org.scalacheck.{ Arbitrary, ConsoleReporter, Prop, Properties }
import org.scalacheck.Arbitrary.{arbitrary, arbThrowable}
import org.scalacheck.Gen.oneOf
import org.scalacheck.util.StdRand
import org.scalacheck.Prop._
import org.scalacheck.ConsoleReporter.{testReport, propReport}
import org.scalacheck.Test.{Params, check}
import org.scalacheck.ConsoleReporter.testStatsEx
import Function.tupled

object CheckEither extends Properties("Either") {
  implicit def arbitraryEither[X, Y](implicit xa: Arbitrary[X], ya: Arbitrary[Y]): Arbitrary[Either[X, Y]] = 
    Arbitrary[Either[X, Y]](oneOf(arbitrary[X].map(Left(_)), arbitrary[Y].map(Right(_))))

  val prop_either1 = forAll((n: Int) => Left(n).fold(x => x, b => error("fail")) == n)

  val prop_either2 = forAll((n: Int) => Right(n).fold(a => error("fail"), x => x) == n)

  val prop_swap = forAll((e: Either[Int, Int]) => e match {
    case Left(a) => e.swap.right.get == a
    case Right(b) => e.swap.left.get == b
  })
  
  val prop_isLeftRight = forAll((e: Either[Int, Int]) => e.isLeft != e.isRight)

  object CheckLeftProjection {
    val prop_value = forAll((n: Int) => Left(n).left.get == n)

    val prop_getOrElse = forAll((e: Either[Int, Int], or: Int) => e.left.getOrElse(or) == (e match {
      case Left(a) => a
      case Right(_) => or
    }))

    val prop_forall = forAll((e: Either[Int, Int]) =>
      e.left.forall(_ % 2 == 0) == (e.isRight || e.left.get % 2 == 0))

    val prop_exists = forAll((e: Either[Int, Int]) =>
      e.left.exists(_ % 2 == 0) == (e.isLeft && e.left.get % 2 == 0))
  
    val prop_flatMapLeftIdentity = forAll((e: Either[Int, Int], n: Int, s: String) => {
      def f(x: Int) = if(x % 2 == 0) Left(s) else Right(s)
      Left(n).left.flatMap(f(_)) == f(n)})

    val prop_flatMapRightIdentity = forAll((e: Either[Int, Int]) => e.left.flatMap(Left(_)) == e)

    val prop_flatMapComposition = forAll((e: Either[Int, Int]) => {
      def f(x: Int) = if(x % 2 == 0) Left(x) else Right(x)
      def g(x: Int) = if(x % 7 == 0) Right(x) else Left(x)
      e.left.flatMap(f(_)).left.flatMap(g(_)) == e.left.flatMap(f(_).left.flatMap(g(_)))})

    val prop_mapIdentity = forAll((e: Either[Int, Int]) => e.left.map(x => x) == e)

    val prop_mapComposition = forAll((e: Either[String, Int]) => {
      def f(s: String) = s.toLowerCase
      def g(s: String) = s.reverse
      e.left.map(x => f(g(x))) == e.left.map(x => g(x)).left.map(f(_))})

    val prop_filter = forAll((e: Either[Int, Int], x: Int) => e.left.filter(_ % 2 == 0) ==
      (if(e.isRight || e.left.get % 2 != 0) None else Some(e)))

    val prop_seq = forAll((e: Either[Int, Int]) => e.left.toSeq == (e match {
      case Left(a) => Seq(a)
      case Right(_) => Seq.empty
    }))

    val prop_option = forAll((e: Either[Int, Int]) => e.left.toOption == (e match {
      case Left(a) => Some(a)
      case Right(_) => None
    }))
  }

  object CheckRightProjection {
    val prop_value = forAll((n: Int) => Right(n).right.get == n)

    val prop_getOrElse = forAll((e: Either[Int, Int], or: Int) => e.right.getOrElse(or) == (e match {
      case Left(_) => or
      case Right(b) => b
    }))

    val prop_forall = forAll((e: Either[Int, Int]) =>
      e.right.forall(_ % 2 == 0) == (e.isLeft || e.right.get % 2 == 0))

    val prop_exists = forAll((e: Either[Int, Int]) =>
      e.right.exists(_ % 2 == 0) == (e.isRight && e.right.get % 2 == 0))

    val prop_flatMapLeftIdentity = forAll((e: Either[Int, Int], n: Int, s: String) => {
      def f(x: Int) = if(x % 2 == 0) Left(s) else Right(s)
      Right(n).right.flatMap(f(_)) == f(n)})

    val prop_flatMapRightIdentity = forAll((e: Either[Int, Int]) => e.right.flatMap(Right(_)) == e)

    val prop_flatMapComposition = forAll((e: Either[Int, Int]) => {
      def f(x: Int) = if(x % 2 == 0) Left(x) else Right(x)
      def g(x: Int) = if(x % 7 == 0) Right(x) else Left(x)
      e.right.flatMap(f(_)).right.flatMap(g(_)) == e.right.flatMap(f(_).right.flatMap(g(_)))})

    val prop_mapIdentity = forAll((e: Either[Int, Int]) => e.right.map(x => x) == e)

    val prop_mapComposition = forAll((e: Either[Int, String]) => {
      def f(s: String) = s.toLowerCase
      def g(s: String) = s.reverse
      e.right.map(x => f(g(x))) == e.right.map(x => g(x)).right.map(f(_))})

    val prop_filter = forAll((e: Either[Int, Int], x: Int) => e.right.filter(_ % 2 == 0) ==
      (if(e.isLeft || e.right.get % 2 != 0) None else Some(e)))

    val prop_seq = forAll((e: Either[Int, Int]) => e.right.toSeq == (e match {
      case Left(_) => Seq.empty
      case Right(b) => Seq(b)
    }))

    val prop_option = forAll((e: Either[Int, Int]) => e.right.toOption == (e match {
      case Left(_) => None
      case Right(b) => Some(b)
    }))
  }

  val prop_Either_left = forAll((n: Int) => Left(n).left.get == n)
  
  val prop_Either_right = forAll((n: Int) => Right(n).right.get == n)

  val prop_Either_joinLeft = forAll((e: Either[Either[Int, Int], Int]) => e match {
    case Left(ee) => e.joinLeft == ee
    case Right(n) => e.joinLeft == Right(n)
  })

  val prop_Either_joinRight = forAll((e: Either[Int, Either[Int, Int]]) => e match {
    case Left(n) => e.joinRight == Left(n)
    case Right(ee) => e.joinRight == ee
  })

  val prop_Either_reduce = forAll((e: Either[Int, Int]) => 
    e.merge == (e match {
      case Left(a) => a
      case Right(a) => a
    }))
    
  /** Hard to believe I'm "fixing" a test to reflect B before A ... */
  val prop_Either_cond = forAll((c: Boolean, a: Int, b: Int) =>
    Either.cond(c, a, b) == (if(c) Right(a) else Left(b)))

  val tests = List(
      ("prop_either1", prop_either1),
      ("prop_either2", prop_either2),
      ("prop_swap", prop_swap),
      ("prop_isLeftRight", prop_isLeftRight),
      ("Left.prop_value", CheckLeftProjection.prop_value),
      ("Left.prop_getOrElse", CheckLeftProjection.prop_getOrElse),
      ("Left.prop_forall", CheckLeftProjection.prop_forall),
      ("Left.prop_exists", CheckLeftProjection.prop_exists),
      ("Left.prop_flatMapLeftIdentity", CheckLeftProjection.prop_flatMapLeftIdentity),
      ("Left.prop_flatMapRightIdentity", CheckLeftProjection.prop_flatMapRightIdentity),
      ("Left.prop_flatMapComposition", CheckLeftProjection.prop_flatMapComposition),
      ("Left.prop_mapIdentity", CheckLeftProjection.prop_mapIdentity),
      ("Left.prop_mapComposition", CheckLeftProjection.prop_mapComposition),
      ("Left.prop_filter", CheckLeftProjection.prop_filter),
      ("Left.prop_seq", CheckLeftProjection.prop_seq),
      ("Left.prop_option", CheckLeftProjection.prop_option),
      ("Right.prop_value", CheckRightProjection.prop_value),
      ("Right.prop_getOrElse", CheckRightProjection.prop_getOrElse),
      ("Right.prop_forall", CheckRightProjection.prop_forall),
      ("Right.prop_exists", CheckRightProjection.prop_exists),
      ("Right.prop_flatMapLeftIdentity", CheckRightProjection.prop_flatMapLeftIdentity),
      ("Right.prop_flatMapRightIdentity", CheckRightProjection.prop_flatMapRightIdentity),
      ("Right.prop_flatMapComposition", CheckRightProjection.prop_flatMapComposition),
      ("Right.prop_mapIdentity", CheckRightProjection.prop_mapIdentity),
      ("Right.prop_mapComposition", CheckRightProjection.prop_mapComposition),
      ("Right.prop_filter", CheckRightProjection.prop_filter),
      ("Right.prop_seq", CheckRightProjection.prop_seq),
      ("Right.prop_option", CheckRightProjection.prop_option),
      ("prop_Either_left", prop_Either_left),
      ("prop_Either_right", prop_Either_right),      
      ("prop_Either_joinLeft", prop_Either_joinLeft),
      ("prop_Either_joinRight", prop_Either_joinRight),      
      ("prop_Either_reduce", prop_Either_reduce),      
      ("prop_Either_cond", prop_Either_cond)
    )
  
  for ((label, prop) <- tests) {
    property(label) = prop
  }
  
  import org.scalacheck.{ Test => STest }
  
  def runTests() = {
    STest.checkProperties(STest.Params(testCallback = ConsoleReporter(0)), this)
  }
}

object Test {
  def main(args: Array[String]): Unit = {
    CheckEither.runTests()
  }
}