shapeless lazy example

CsvEncoder.scala

import shapeless._

trait CsvEncoder[A] {
  def encode(value: A): List[String]
}

object CsvEncoder {
  def apply[A](implicit encoder: CsvEncoder[A]): CsvEncoder[A] =
    encoder

  def pure[A](func: A => List[String]): CsvEncoder[A] =
    new CsvEncoder[A] {
      def encode(value: A): List[String] = func(value)
    }
}

implicit val intEncoder: CsvEncoder[Int] =
  CsvEncoder.pure(num => List(num.toString))

implicit val hnilEncoder: CsvEncoder[HNil] =
  CsvEncoder.pure(hnil => Nil)

implicit def hlistEncoder[H, T <: HList](
  implicit
  hEncoder: Lazy[CsvEncoder[H]],
  tEncoder: CsvEncoder[T]
): CsvEncoder[H :: T] =
  CsvEncoder.pure(pair => hEncoder.value.encode(pair.head) ++ tEncoder.encode(pair.tail))

implicit val cnilEncoder: CsvEncoder[CNil] =
  CsvEncoder.pure(cnil => ???)

implicit def coproductEncoder[H, T <: Coproduct](
  implicit
  hEncoder: Lazy[CsvEncoder[H]],
  tEncoder: CsvEncoder[T]
): CsvEncoder[H :+: T] =
  CsvEncoder.pure {
    case Inl(h) => hEncoder.value.encode(h)
    case Inr(t) => tEncoder.encode(t)
  }

implicit def genericEncoder[A, R](
  implicit
  gen: Generic.Aux[A, R],
  rEncoder: Lazy[CsvEncoder[R]]
): CsvEncoder[A] =
  CsvEncoder.pure(value => rEncoder.value.encode(gen.to(value)))

sealed trait Tree[A]
final case class Branch[A](left: Tree[A], right: Tree[A]) extends Tree[A]
final case class Leaf[A](value: A) extends Tree[A]

implicitly[CsvEncoder[Tree[Int]]]

I am confused!

If I paste this whole lot into the REPL, it fails to find an instance for CsvEncoder.

If I paste everything bar the last line, then paste the last line, it works fine.

If I run this code from the tut examples in shapeless-guide, it sends the compiler into an infinite loop. Probably because I'm redefining certain definitions.