tagged-type-play-json.scala

import play.api.libs.json.{Format, JsResult, JsValue, Json}
import shapeless.tag.@@

trait Money

case class Amount(price: String @@ Money)

private val amountWrites = Json.writes[Amount]
private val amountReads = Json.reads[Amount]

implicit val format: Format[Amount] = new Format[Amount] {
  override def writes(amount: Amount): JsValue = Json.toJson(amount)(amountWrites)

  override def reads(json: JsValue): JsResult[Amount] = Json.fromJson[Amount](json)(amountReads)
}

implicit val formatMoney: Format[String @@ Money] = new Format[@@[String, Money]] {
  override def writes(o: @@[String, Money]): JsValue = Json.toJson(o)(Json.writes[String @@ Money])

  override def reads(json: JsValue): JsResult[@@[String, Money]] = Json.fromJson[String @@ Money](json)(Json.reads[String @@ Money])
}