http://stackoverflow.com/questions/38679873/diverging-implicits-for-case-class-w-case-class-argument

GenericDerivTest.scala

package net

import scala.util._
import shapeless._

object Test {

  case class Person(name: String, age: Double)
  case class PersonWrapper(person: Person, x: Int)

  trait Parser[A] {
    def apply(s: String): Option[A]
  }

  implicit val hnilParser: Parser[HNil] = new Parser[HNil] {
    def apply(s: String): Option[HNil] = if(s.isEmpty) Some(HNil) else None
  }

  implicit def hconsParser[H: Parser, T <: HList: Parser]: Parser[H :: T] = new Parser[H :: T] {
    def apply(s: String): Option[H :: T] = s.split(",").toList match {
      case cell +: rest => for {
        head <- implicitly[Parser[H]].apply(cell)
        tail <- implicitly[Parser[T]].apply(rest.mkString(","))
      } yield head :: tail
    }
  }

  implicit val stringParser: Parser[String] = new Parser[String] {
    def apply(s: String): Option[String] = Some(s)
  }

  implicit val intParser: Parser[Int] = new Parser[Int] {
    def apply(s: String): Option[Int] = Try(s.toInt).toOption
  }

  implicit val doubleParser: Parser[Double] = new Parser[Double] {
    def apply(s: String): Option[Double] = Try(s.toDouble).toOption
  }

  implicit def caseClassParser[A, R <: HList](implicit gen: Generic[A] { type Repr = R },
                                              reprParser: Parser[R]): Parser[A] =
    new Parser[A] {
      def apply(s: String): Option[A] = reprParser.apply(s).map(gen.from)
    }


  object Parser {
    def apply[A](s: String)(implicit parser: Parser[A]): Option[A] = parser(s)
  }

}


/*
scala> import net.Test._
import net.Test._

scala> Parser[PersonWrapper]("kevin,66,42")
<console>:15: error: diverging implicit expansion for type net.Test.Parser[net.Test.PersonWrapper]
starting with method caseClassParser in object Test
       Parser[PersonWrapper]("kevin,66,42")
                            ^
*/