let
  config = config: {
    inherit config;

    packageOverrides = pkgs: rec {
      haskellPackages = pkgs.haskellPackages.override {
        overrides = haskellPackagesNew: haskellPackagesOld: rec {
          myProject = haskellPackages.callPackage ./default.nix {};
        };
      };
    };
  };

  pkgs = import <nixpkgs> { inherit config; };

in
  { myProject = pkgs.haskellPackages.myProject;
  }