my config.nix

config.nix

{
  packageOverrides = pkgs: rec {
    #                                                                                                               
    hepNixOverlay =
      let self = pkgs.callPackage /home/wavewave/repo/src/hep-nix-overlay {};
      in pkgs.recurseIntoAttrs self;
    #                                                                                                               
    yesodEnv =
      let hsenv = with (pkgs // pkgs.haskellPackages); ghcWithPackages
            (self : [ cabalInstall
                  hjsmin persistentSqlite split hastache
                  yesod yesodStatic cryptohashConduit classyPreludeConduit
            ]);
      in pkgs.myEnvFun {
           name = "yesod";
       buildInputs = with pkgs; [ hsenv hepNixOverlay.FeynHiggs ];
       extraCmds = ''
         $(grep export ${hsenv.outPath}/bin/ghc)
           '';
         };
    };
}