No need for Lazy now

nolazy.scala

import shapeless.{::, Generic, HList, HNil}

case class StringWrapper(s: String)

trait F[W, V]

object F {
  implicit def genWV[W, V, Repr <: HList](implicit
                                 gen: Generic.Aux[W, Repr],
                                 ev: (V :: HNil) =:= Repr
                                ): F[W, V] = new F[W, V] {}
}

trait G[V]

object G {
  implicit def genG[W, V](implicit
                          f: F[W, V],
                          g: G[V]
                         ): G[W] = new G[W] {}

  implicit val fString = new G[String] {}
}

object Test1 {
  val f = implicitly[G[StringWrapper]]
}

object Test {
  val g = implicitly[G[StringWrapper]]
}