Selectors

aux.scala

val book =
    ('author ->> "Benjamin Pierce") ::
    ('title  ->> "Types and Programming Languages") ::
    ('id     ->>  262162091) ::
    ('price  ->>  44.11d) ::
    HNil

  def readBook[B <: HList](book:B)(implicit
    author: Selector.Aux[B, Witness.`'author`.T, String],
    title: Selector.Aux[B, Witness.`'title`.T, String],
    price: Selector.Aux[B, Witness.`'price`.T, Double]
  ): Unit = {
    println(s"${author(book)}: ${title(book)}, ${price(book)}")
  }