HList Reads

gistfile1.scala

/**
 * Based on
 * https://github.com/mandubian/shapelaysson/blob/master/src/main/scala/shapelaysson.scala
 */
package object test {
  import shapeless._
  import shapeless.HList._
  import play.api.libs.json._
  import play.api.libs.functional.Functor
  import play.api.libs.functional.syntax._
  import scala.{:: => ::|}

  private implicit val `JsResult Functor` = new Functor[JsResult] {
    def fmap[A, B](m: JsResult[A], f: (A) => B) = m.map(f)
  }

  implicit def hlistReads[H : Reads, T <: HList : Reads]: Reads[H :: T] = Reads {
    _.validate[JsArray].map(_.value.toList).flatMap {
      case head ::| tail => (head.validate[H] ~ JsArray(tail).validate[T])(_ :: _)
      case _ => JsError("can't convert empty list using multi-element HList")
    }
  }

  implicit def hnilReads: Reads[HNil] = Reads {
    case JsArray(values) if values.isEmpty => JsSuccess(HNil)
    case _ => JsError("Not empty JsArray")
  }
}