allen.scala

trait Interpreter[F[_]] {
  def int(i: Int): F[Int]
  def add(lhs: F[Int], rhs: F[Int]): F[Int]
}

trait Calc[A] {
  def run[F[_]](interp: Interpreter[F]): F[A]
}

object Calc {
  def int(i: Int): Calc[Int] = ???
  def add(lhs: Calc[Int], rhs: Calc[Int]): Calc[Int] = ???
}

trait Opaque {
    type I[X[_]];
    type F[_];

    def int(i: Int): this.F[Int]
    def add(lhs: this.F[Int], rhs: this.F[Int]): this.F[Int]
}

object Help {
  trait IO[_] {}

  trait Const[A] { type L[B] = A }
}

import Help._

trait Serializer0 extends Opaque {
  type I[X[_]] = Interpreter[X];
  type F[A] = Const[IO[A]]#L; // this doesn't check

  def int(i: Int): IO[Unit] = ???
  def add(lhs: IO[Unit], rhs: IO[Unit]): IO[Unit] = ???
}
//
// // A working impl would be something like, but now the `Json` format is exposed
// // and inspectable.. main problem is trying to avoid this
// trait JsonSerializaer extends Interpreter[Const[Json]#l] {
//   def int(i: Int): Json = JNumber(i)
//   def add(lhs: Json, rhs: Json): Json = JObject(("+", JList(lhs, rhs)))
// }