discipline for Prob Monad

ex01_ProbMonadSpec.scala

package ex01

import cats.Eq
import cats.laws.discipline.MonadTests
import ex01.Prob.Event
import ex01.ProbInstances._
import org.scalacheck.{Gen, _}
import org.scalatest.FunSuite
import org.typelevel.discipline.scalatest.Discipline

class ProbMonadSpec extends FunSuite with Discipline {

  implicit def defaultEq[A]: Eq[A] = (x, y) => x == y

  implicit def genRational: Gen[Rational] = for {
    n <- Gen.choose(-3, 3)
    d <- Gen.choose(-3, 3).retryUntil(_ != 0)
  } yield Rational.apply(n, d)
  implicit def arbRational: Arbitrary[Rational] = Arbitrary(genRational)

  implicit def genProb[A](implicit arb: Arbitrary[List[Event[A]]]): Gen[Prob[A]] =
    arb.arbitrary.map(Prob(_))
  implicit def arbProb[A](implicit arb: Arbitrary[A]): Arbitrary[Prob[A]] = Arbitrary(genProb[A])

  implicit def genCoin: Gen[Coin] = Gen.oneOf[Coin](Heads, Tails)
  implicit def cogenCoin: Cogen[Coin] = Cogen { _ match {
    case Heads => 1L
    case Tails => 0L
  }}
  implicit def arbCoin: Arbitrary[Coin] = Arbitrary(genCoin)

  checkAll("Monad[Prob[Coin]]", MonadTests[Prob].monad[Coin, Coin, Coin])
}