open list

val rec map [a, b] (f: (consumes a -> b), consumes xs: list a): list b =
  match xs with
  | Cons { head = h; tail = t } ->
      let h' = f h in
      let t' = map (f, t) in
      Cons { head = h'; tail = t' }
  | Nil ->
      xs
  end