final: prev: rec {
  # keep sources this first
  sources = prev.callPackage (import ./_sources/generated.nix) { };
  # then, call packages with `final.callPackage`
  go-fold-if-err-nil = final.callPackage ./go-fold-if-err-nil.nix { };
  olympus = final.callPackage ./olympus.nix { };
}