Attempt to implement `Init` per shapeless-guide book

X.scala

package net

import shapeless.{::, DepFn1, HList}

trait Init[L <: HList] extends DepFn1[L]

object Init {

  type Aux[L <: HList, Out1] = Init[L] { type Out = Out1}

  def apply[L <: HList](implicit ev: Init[L]): Aux[L, ev.Out] = ev

  implicit def atLeast1[H, L <: HList]: Aux[H :: L, L] =
    new Init[H :: L] {
      type Out = L
      def apply(in: H :: L): Out = in.tail
    }
}

testing

scala> Init[Int :: HNil]
res0: net.Init[shapeless.::[Int,shapeless.HNil]]{type Out = shapeless.HNil} = net.Init$$anon$1@9d5bd06

scala> res0(4 :: HNil)
res1: res0.Out = HNil

scala> Init[Char :: String :: HNil]
res2: net.Init[shapeless.::[Char,shapeless.::[String,shapeless.HNil]]]{type Out = shapeless.::[String,shapeless.HNil]} = net.Init$$anon$1@7c7fb5a2

scala> res2('a' :: "f" :: HNil)
res3: res2.Out = f :: HNil

scala> Init[HNil]
<console>:16: error: could not find implicit value for parameter ev: net.Init[shapeless.HNil]
       Init[HNil]
           ^