anchor.diff:    makeDrv = name: src:
       with pkgs.haskell.lib;
       let
  -      drv =
  -        haskellPackages.callCabal2nix "" src
  -        ({ } // pkgs.lib.optionalAttrs (name == "vulkan") {
  +      drv = haskellPackages.callCabal2nix "" src ({ }
  +        // pkgs.lib.optionalAttrs (name == "vulkan") {
             vulkan = pkgs.vulkan-loader;
           } // pkgs.lib.optionalAttrs ((name == "vulkan-examples" || name
             == "vulkan-utils" || name == "VulkanMemoryAllocator") && forShell) {
  
positive.code:   haskellPackages = with pkgs.haskell.lib;
      pkgs.haskell.packages.${compiler'}.override {
        overrides = self: super:
          (pkgs.lib.mapAttrs (n: v: makeDrv n v) targets) // {
            #
            # Examples
            #
  
negative.code: 
    targets = let
      srcFilter = path: type:
        (baseNameOf path == "package.yaml") || pkgs.lib.hasInfix "/src" path
        || pkgs.lib.hasInfix "/vk" path || pkgs.lib.hasInfix "/vma" path;
      filter = builtins.filterSource srcFilter;
    in {
      vulkan = filter ./.;
  