shell.nix

 let
  myHaskellPackageOverlay = self: super: {
    haskellPackages = super.haskellPackages.override {
    overrides = hself: hsuper: {
        mkDerivation = args: hsuper.mkDerivation (args // {
          doCheck = false;
          doHaddock = false;
          jailbreak = true;
        });

        splitmix = self.fetchFromGitHub {
        owner = "phadej";
        repo = "splitmix";
        rev = "fcf2d95181c0d4c39dbaf80cd28b6498f24e5f74";
        sha256 = "1cw5fszffl5pkpa6s6wjnkiv6lm5k618s32sp60kvmvpy7a2v9kh";
        };

        random =
          let newRandomSrc = builtins.fetchGit {
                url = "https://github.com/idontgetoutmuch/random.git";
                rev = "83262ccd8a2d4b8f29b14c535b6bdf997bc7a497";
                ref = "interface-to-performance";
              };
          in
          # Since cabal2nix has a transitive dependency on random, we need to                                                                            
          # get the callCabal2nix function from the normal haskellPackages that                                                                          
          # is not being overridden.                                                                                                                     
          (import <nixpkgs> {}).haskell.lib.dontCheck ((import <nixpkgs> {}).haskellPackages.callCabal2nix "random" newRandomSrc { });
      };
    };
  };

in

{ pkgs ? import <nixpkgs> { overlays = [ myHaskellPackageOverlay ]; }, doBenchmark ? false }:

let
  foo = pkgs.fetchFromGitHub {
    owner = "phadej";
    repo = "splitmix";
    rev = "fcf2d95181c0d4c39dbaf80cd28b6498f24e5f74";
    sha256 = "1cw5fszffl5pkpa6s6wjnkiv6lm5k618s32sp60kvmvpy7a2v9kh";
  };

  haskellDeps = ps: with ps; [
    random    # (pkgs.haskell.lib.dontCheck random)                                                                                                      
    foo  # (pkgs.haskell.lib.doJailbreak splitmix)                                                                                                       
  ];

in

  pkgs.stdenv.mkDerivation {
  name = "env";
  buildInputs = [
    (pkgs.haskellPackages.ghcWithPackages haskellDeps)
  ];
}