λ(nix : ../NixPrelude.dhall) →
  let Optional/map =
        https://raw.githubusercontent.com/dhall-lang/dhall-lang/v22.0.0/Prelude/Optional/map.dhall
          sha256:501534192d988218d43261c299cc1d1e0b13d25df388937add784778ab0054fa

  let max = ./max.dhall nix

  let listMax
      : List Double → Optional Double
      = λ(xs : List Double) →
          Optional/map
            Double
            Double
            (λ(n : Double) → List/fold Double xs Double max n)
            (List/head Double xs)

  in  listMax