{
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, flake-utils }: flake-utils.lib.eachDefaultSystem (system:
    let
      inherit (nixpkgs) lib;
      pkgs = import nixpkgs { inherit system; };
      mkNocheck = drv: drv.overrideAttrs (o: {
        doCheck = false;
        checkInputs = [ ];
      });
      mkClang = drv: drv.override (o: {
        stdenv = pkgs.clangStdenv;
      });
    in
    {
      packages = lib.foldAttrs lib.const { }
        (lib.flatten (lib.mapAttrsToList
          (name: v: {
            "${name}" = v;
            "${name}-nocheck" = mkNocheck v;
            "${name}-clang" = mkClang v;
            "${name}-nocheck-clang" = mkClang (mkNocheck v);
          })
          rec {
            u01 = pkgs.callPackage
              ({ stdenv, catch2_3, cmake }: stdenv.mkDerivation {
                name = "ecg-u01";

                src = ./u01;

                nativeBuildInputs = [ cmake ];
                checkInputs = [ catch2_3 ];

                doCheck = true;
              })
              { };

            u02 = pkgs.callPackage
              ({ stdenv, catch2_3, cmake, freeglut, libGL, libGLU }: stdenv.mkDerivation {
                name = "ecg-u02";

                src = ./u02;

                nativeBuildInputs = [ cmake ];
                buildInputs = [ freeglut libGL libGLU ];
                checkInputs = [ catch2_3 ];

                doCheck = true;
              })
              { };

            u03 = pkgs.callPackage
              ({ stdenv, cmake, freeglut, libGL, libGLU }: stdenv.mkDerivation {
                name = "ecg-u03";

                src = ./u03;

                nativeBuildInputs = [ cmake ];
                buildInputs = [ freeglut libGL libGLU ];
              })
              { };
          }));

      devShells.default = pkgs.mkShell {
        nativeBuildInputs = with pkgs; [ catch2_3 clang cmake freeglut libGL libGLU reuse ];
      };
    });
}