shapes.scala

sealed trait Shape[P]

case class Void[P]() extends Shape[P]
case class Unit[P]() extends Shape[P]
case class Value[P, A](a: A) extends Shape[P]
case class Meta[P, T <: Tag](shape: Shape[P]) extends Shape[P]
sealed trait Sum[P] extends Shape[P] {
  val shape: Shape[P]
}
case class Left[P](shape: Shape[P]) extends Sum[P]
case class Right[P](shape: Shape[P]) extends Sum[P]
case class Product[P](left: Shape[P], right: Shape[P]) extends Shape[P]

sealed trait Tag
trait Datatype extends Tag
trait Constructor extends Tag
trait RecordSelector extends Tag


// inu
sealed trait Dog
case class ShibaInu(name: String) extends Dog
case object NotInu extends Dog

object Main {
  def genericDogFrom(dog: Dog) = dog match {
    case ShibaInu(name) => Meta[Dog, Datatype](Left[Dog](Meta[Dog, Constructor](Meta[Dog, RecordSelector](Value[Dog, String](name)))))
    case NotInu => Meta[Dog, Datatype](Right[Dog](Meta[Dog, Constructor](Unit[Dog]())))
  }

  // json
  def toJSON[A](rep: Shape[A]): String = rep match {
    case Void() => "{}"
    case Unit() => "{}"
    case Value(x) => "\"" ++ x.toString ++ "\""
    case Meta(v) => toJSON(v)
    case Left(s) => s"[false, ${toJSON(s)}]"
    case Right(s) => s"[true, ${toJSON(s)}]"
    case Product(l, r) => s"[${toJSON(l)}, ${toJSON(r)}]"
  }

}