λ(nix : ../NixPrelude.dhall) →
  let List/filterMap = ./filterMap.dhall nix

  let unpackOptionals
      : ∀(a : Type) → ∀(l : List (Optional a)) → List a
      = λ(a : Type) → List/filterMap (Optional a) a (λ(x : Optional a) → x)

  in  unpackOptionals