Scalacheck generator for iota coproduct (No longer necessary after this http://bit.ly/2EFdY4k)

iotaGen.scala

// This is an ammonite scala script see:  http://bit.ly/2FyQf58

// Dependencies
import $ivy.`org.typelevel::cats-core:1.0.1`
import $ivy.`com.chuusai::shapeless:2.3.3`
import $ivy.`io.frees::iota-core:0.3.4`
import $ivy.`org.scalacheck::scalacheck:1.13.5`

// Regular imports
import iota.{ Cop, TNil }
import iota.TList.::
import iota.syntax.inject._
import org.scalacheck.Gen

object Monday
object Tuesday
object Wednesday
object Thursday
object Friday

type Weekday =
  Cop[Monday.type :: Tuesday.type :: Wednesday.type :: Thursday.type :: Friday.type :: TNil]

// This won't compile as `Gen.oneOf` works with regular sequences so
// iota won't find a proper instance for the `Inject` typeclass

//val weekdayGen: Gen[Weekday] =
//  Gen.oneOf(Monday, Tuesday, Wednesday, Thursday, Friday).map(_.inject[Weekday])

//iotaGen.sc:24: could not find implicit value for parameter ev: iota.Cop.Inject[Object,ammonite.$file.iotaGen.Weekday]
//Gen.oneOf(Monday, Tuesday, Wednesday, Thursday, Friday).map(_.inject[Weekday])

// We need to track the types, e.g.:

import shapeless.{ HNil, Poly1 }
object injectToWeekday extends Poly1 {
  implicit def genericCase[A](implicit ev: Cop.Inject[A, Weekday]) =
    at[A](_.inject[Weekday])
}

val weekdayGen: Gen[Weekday] =
  Gen.oneOf(
    (Monday :: Tuesday :: Wednesday :: Thursday :: Friday :: HNil).map(injectToWeekday).toList
  )

// It works!
println(weekdayGen.sample)
// Some(Cop(ammonite.$file.iotaGen$Monday$@3c5fc608 @ 0))
println(weekdayGen.sample)
// Some(Cop(ammonite.$file.iotaGen$Friday$@277d8c08 @ 4))
println(weekdayGen.sample)
// Some(Cop(ammonite.$file.iotaGen$Wednesday$@7f7f6805 @ 2))