HListDeserializer

gistfile1.scala

import shapeless._
import shapeless.poly._
import shapeless.ops.hlist._
import scala.util.Try

trait Deserializer[A, B] {
  def apply(t: A): Either[String, B]
}

object Deserializer {
  implicit def identity[A] = new Deserializer[A, A] {
    def apply(t: A) = Right(t)
  }

  implicit def stringToInt = new Deserializer[String, Int] {
    def apply(s: String) = try Right(s.toInt) catch { case _ => Left("error") }
  }
}

trait DeserializeTo[In <: HList, Out <: HList] {
  def apply(l: In): Out
}

object DeserializeTo {
  private class BubbleLeftException(val left: Left[Any, Any]) extends RuntimeException

  implicit def hnilDeserializer: DeserializeTo[HNil, HNil] =
    new DeserializeTo[HNil, HNil] {
      def apply(l: HNil) = HNil
    }
  
  implicit def hlistDeserializer[InH, InT <: HList, OutH, OutT <: HList](implicit des: Deserializer[InH, OutH], dt: DeserializeTo[InT, OutT]) =
    new DeserializeTo[InH :: InT, OutH :: OutT] {
      def apply(l: InH :: InT) = des(l.head) match {
        case Right(x) => x :: dt(l.tail)
        case left: Left[_, _] => throw new BubbleLeftException(left)
      }
    }
}

case class HListDeserializer[T](implicit gen: Generic[T] { type Repr <: HList }) {
  def apply[L <: HList](l: L)(implicit des: DeserializeTo[L, gen.Repr]) = gen.from(des(l))
}

case class Foo(i1: Int, i2: Int)

val des = HListDeserializer[Foo]
des(1 :: 2 :: HNil)

// <console>:31: error: could not find implicit value for parameter des: DeserializeTo[shapeless.::[Int,shapeless.::[Int,shapeless.HNil]],des.gen.Repr]
// des(1 :: 2 :: HNil)
// ^