gistfile1.txt

  haskellPackages =
    pkgs.haskellPackages.override {
      overrides = self: super:
        let
          mk-packagedb =
            packages:
            pkgs.runCommand "make-package-db" {}
              ''
              mkdir $out
              ${ pkgs.lib.concatMapStringsSep
                "\n"
                ( pkg: "cp -f ${pkg}/lib/ghc-8.6.5/package.conf.d/*.conf $out/" )
                packages }
              ${self.ghc}/bin/ghc-pkg --package-db="$out" recache
              '';

        in
        {
          ghc-nix =
            self.callPackage ../ghc-nix {};

          fused-effects =
            ( pkgs.haskell.lib.overrideCabal
              super.fused-effects
              ( args:
                { configureFlags = [ "-w ${self.ghc-nix}/bin/ghc-nix" ];
                  buildTools = [ pkgs.which nix ];
                  postConfigure = "ls -l /build/package.conf.d ; echo $PACKAGE_DB";
                }
              ) ).overrideAttrs ( oldAttrs: {
                requiredSystemFeatures = [ "recursive-nix" ];
                NIX_PATH = pkgs.path;
                PACKAGE_DB = mk-packagedb ( builtins.filter ( x: x != null ) ( super.fused-effects.buildInputs ++ super.fused-effects.propagatedBuildInputs ) );
              });
        };
    };