env_effect_without_subtyping.scala

object EnvEffetWithoutSubtyping {

  import EnvEffetWithoutSubtyping.Alg1.HasAlg1
  import EnvEffetWithoutSubtyping.Alg2.HasAlg2
  import EnvEffetWithoutSubtyping.Alg3.HasAlg3

  trait Alg1
  object Alg1 {
    trait HasAlg1[E] {
      def alg1(e: E): Alg1
    }
  }
  trait Alg2
  object Alg2 {
    trait HasAlg2[E] {
      def alg2(e: E): Alg2
    }
  }
  trait Alg3
  object Alg3 {
    trait HasAlg3[E] {
      def alg3(e: E): Alg3
    }
  }

  final case class SmallEnv(alg1: Alg1, alg2: Alg2)
  object SmallEnv {
    implicit val env1: HasAlg1[SmallEnv] = _.alg1
    implicit val env2: HasAlg2[SmallEnv] = _.alg2
  }

  final case class BigEnv(alg1: Alg1, alg2: Alg2, alg3: Alg3)
  object BigEnv {
    implicit val env1: HasAlg1[BigEnv] = _.alg1
    implicit val env2: HasAlg2[BigEnv] = _.alg2
    implicit val env3: HasAlg3[BigEnv] = _.alg3
  }

  def program[Env: HasAlg1: HasAlg2: HasAlg3](): Kleisli[Id, Env, Unit] = {

    def innerF1[InnerEnv: HasAlg1]: Reader[InnerEnv, Unit]                   = ???
    def innerF2[InnerEnv: HasAlg2]: Reader[InnerEnv, Unit]                   = ???
    def innerF3[InnerEnv: HasAlg1: HasAlg2]: Reader[InnerEnv, Unit]          = ???
    def innerF4[InnerEnv: HasAlg1: HasAlg2: HasAlg3]: Reader[InnerEnv, Unit] = ???

    for {
      _ <- innerF1
      _ <- innerF2
      _ <- innerF3
      _ <- innerF4
    } yield ()

  }

  program[BigEnv]()

}