PoC of scalacheck free definition of laws

poc_scalacheck_free_laws.scala

trait RuleSetDSL[P] {

  type Check1[A1, A2] = Checkable1[A1, A2, P]
  type Check2[A1, A2, A3] = Checkable2[A1, A2, A3, P]

  implicit def law[A1, A2](s : String, f: A1 => IsEq[A2])(implicit toP1: Check1[A1, A2]): (String, P) =
    (s, toP1(f))

  implicit def law[A1, A2, A3](s : String, f: (A1, A2) => IsEq[A3])(implicit toP2: Check2[A1, A2, A3]): (String, P) =
    (s, toP2(f))
}

class MyRuleSet[P] extends RuleSetDSL[P] {

  private def mylaw[A]= (a:A) => IsEq(a, a)
  private def mylaw2[A, B]= (a:A, b: B) => IsEq(a, a)



  def props[A, B](implicit toP : Check1[A, A],
                  toP2: Check2[A, B, A]): Seq[(String, P)] =
    Seq(law("dbad", mylaw[A]),
        law("bgdf", mylaw2[A, B]))

}

trait Checkable1[A1, A2, P] {
  def apply(f: A1 => IsEq[A2]): P
}

trait Checkable2[A1, A2, A3, P] {
  def apply(f: (A1, A2) => IsEq[A3]): P
}

import org.scalacheck.util.Pretty

class RunnerBase {

  def checkAll(p: Seq[(String, Prop)]): Unit = ???

  import cats.kernel.Eq

  implicit def catsLawsIsEqToProp[A](isEq: IsEq[A])(implicit ev: Eq[A], pp: A => Pretty): Prop =
    isEq match {
      case IsEq(x, y) =>
        if (ev.eqv(x, y)) Prop.proved
        else
          Prop.falsified :| {
            val exp = Pretty.pretty[A](y, Pretty.Params(0))
            val act = Pretty.pretty[A](x, Pretty.Params(0))
            s"Expected: $exp\n" + s"Received: $act"
          }
    }

  implicit def tp1[A1: Arbitrary, A2](implicit ev: Eq[A2], pp: A2 => Pretty): Checkable1[A1, A2, Prop] = { f =>
    forAll((a: A1) => f(a))
  }

  implicit def tp2[A1: Arbitrary, A2: Arbitrary, A3](implicit ev: Eq[A3], pp: A3 => Pretty): Checkable2[A1, A2, A3, Prop] = { f =>
    forAll((a:A1, b: A2) => f(a,b))
  }


}


class MyRunner extends RunnerBase {
  import cats.kernel.instances.string._


  checkAll(new MyRuleSet[Prop].props[String, String])
}