Use Poly1 to Map HList

HListMap.scala

import shapeless._

object size extends Poly1 {
  implicit def default[T] = at[T](t => (t, 1))

  implicit def caseInt = at[Int](x => (x, x))

  implicit def caseString = at[String](s => (s, s.length))
}

val hl = "one" :: 2 :: "three" :: HNil

hl.map(size)

hl.map(size).toList