Exploring everywhere

json.scala

import shapeless._, poly._

object SYBMain extends App {

  // Play JSON boils down to:
  sealed trait JsValue

  case object JsNull extends JsValue

  case class JsObject  (fields: Seq[(String, JsValue)]) extends JsValue
  case class JsNumber  (value : BigDecimal)             extends JsValue
  case class JsArray   (value : Seq[JsValue] = List())  extends JsValue
  case class JsString  (value : String)                 extends JsValue
  case class JsBoolean (value : Boolean)                extends JsValue

  val tree : JsValue =
    JsObject(Seq(
      ("cat", JsNumber(1)),
      ("dog", JsNumber(2)),
      ("fox", JsNull)
     )
    )

  object fix extends Poly1 {
    implicit def bigger = at[BigDecimal](_ * 987654321)
  }

  println(
    everywhere(fix)(tree)
  )

  // Result:
  // JsObject(List((cat,JsNumber(1)), (dog,JsNumber(2)), (fox,JsNull)))

  // Desired (bigger applied):
  // JsObject(List((cat,JsNumber(987654321)), (dog,JsNumber(1975308642)), (fox,JsNull)))


  // This is exploring.
  // The true aim is to be able to write something to remove (_,JsNull)
  // that occurs anywhere in a JsValue tree.

}