Prelude

Purely functional parallelism

(Chapter 7)

Choosing data types and functions

Property based testing

(Chapter 8)

Choosing data types and functions

def forAll[A](as: Gen[A])(f: A => Boolean): Prop = Prop {
  (n,rng) => randomStream(as)(rng).zip(Stream.from(0)).take(n).map {
    case (a, i) => try {
      if (f(a)) Passed else Falsified(a.toString, i)
    } catch { case e: Exception => Falsified(buildMsg(a, e), i) }
  }.find(_.isFalsified).getOrElse(Passed)
}

def forAll[A](g: SGen[A])(f: A => Boolean): Prop = Prop {
  (max,n,rng) =>
    val casesPerSize = (n - 1) / max + 1
    val props: Stream[Prop] =
      Stream.from(0).take((n min max) + 1).map(i => forAll(g(i))(f))
    val prop: Prop =
      props.map(p => Prop { (max, _, rng) =>
        p.run(max, casesPerSize, rng)
      }).toList.reduce(_ && _)
    prop.run(max,n,rng)
}