{ ... }:
{
  perSystem =
    { lib, pkgs, ... }:
    {
      packages = lib.mapAttrs (
        name: _:
        let
          pkgDir = ./. + "/${name}";
          hasPackageNix = builtins.pathExists (pkgDir + "/package.nix");
          hasDefaultNix = builtins.pathExists (pkgDir + "/default.nix");
        in
        if hasPackageNix then
          pkgs.callPackage (pkgDir + "/package.nix") { }
        else if hasDefaultNix then
          builtins.trace "Warning: ${name} is using deprecated default.nix, please rename to package.nix" (
            pkgs.callPackage pkgDir { }
          )
        else
          throw "Package ${name} has neither package.nix nor default.nix"
      ) (lib.filterAttrs (_n: v: v == "directory") (builtins.readDir ./.));
    };
}