to save you from writing one...

import magnolia._
import org.scalacheck._

import scalaz._, Scalaz._
import scalaz.scalacheck.ScalaCheckBinding._

object ScalacheckMagnolia {
  type Typeclass[A] = Arbitrary[A]

  def combine[A](ctx: CaseClass[Arbitrary, A]): Arbitrary[A] = Arbitrary {
    ctx.parameters.toList.traverse(p => Gen.lzy(p.typeclass.arbitrary)).map { ps =>
      ctx.rawConstruct(ps)
    }
  }

  def dispatch[A](ctx: SealedTrait[Arbitrary, A]): Arbitrary[A] = Arbitrary {
    Gen.frequency(ctx.subtypes.map(s => 1 -> (Gen.lzy(s.typeclass.arbitrary))): _*)
  }

  implicit def gen[A]: Arbitrary[A] = macro Magnolia.gen[A]

}

softwaremill/magnolia#118 (comment)

And there is also one for scalaz-deriving.

softwaremill/magnolia#78

FYI https://gitlab.com/fommil/scalaz-deriving includes

• Equal / Order
• Semigroup / Monoid
• Show
• Arbitrary

and examples

• JsEncoder / JsDecoder
• XEncoder / XDecoder

• #1
• scala-native/scala-native#233

There are some things that I don't think work very well in scalaz-deriving, magnolia is better for them. Typically things that are not lawful (e.g. require access to labels)

• Show
• Arbitrary
• etc

These magnolia instances would work with @deriving if they come with an appropriate deriving.conf file.

However, I think lawful things like Equal, Order, Semigroup, Monoid are best done with lawful typeclasses such as Decidablez, Altz.

https://gitlab.com/fommil/scalaz-deriving/issues/100