configuration.nix

  nixpkgs.config.packageOverrides = pkgs: rec {
    haskellEnv =
      pkgs.haskellPackages.ghcWithPackages (ghcPkgs:
        with ghcPkgs; with pkgs.haskell.lib; [
        # pkgs.haskell.packages.ghc802.ghc-mod
        (let src = pkgs.fetchFromGitHub {
                     owner = "DanielG";
                     repo = "ghc-mod";
                     rev = "9f44a7f3e082c860fab0190a13265ec65ee35987";
                     sha256 = "0qkwbk816w26wadwv2r16xjdfvr6bz5xyi3sn7hbvczdhg3c0xad";
             };
             ghc-mod-core = (doJailbreak (callPackage ./packages/ghc-mod-core.nix {
               inherit src;
             }));
        in (doJailbreak (callPackage ./packages/ghc-mod.nix {
          inherit ghc-mod-core src;
        })))
        ...
    ]);
  environment.systemPackages = with pkgs; [
    haskellEnv
  ];

ghc-mod-core.nix

{ mkDerivation, base, binary, bytestring, cabal-helper, containers
, deepseq, directory, djinn-ghc, extra, fclabels, filepath
, fingertree, ghc, ghc-boot, ghc-paths, ghc-syb-utils
, haskell-src-exts, hlint, monad-control, monad-journal, mtl
, old-time, optparse-applicative, pipes, process, safe, semigroups
, split, stdenv, syb, template-haskell, temporary, text, time
, transformers, transformers-base
, src
}:
mkDerivation {
  pname = "ghc-mod-core";
  inherit src;
  version = "5.9.0.0";
  postUnpack = "sourceRoot=source/core";
  libraryHaskellDepends = [
    base binary bytestring cabal-helper containers deepseq directory
    djinn-ghc extra fclabels filepath fingertree ghc ghc-boot ghc-paths
    ghc-syb-utils haskell-src-exts hlint monad-control monad-journal
    mtl old-time optparse-applicative pipes process safe semigroups
    split syb template-haskell temporary text time transformers
    transformers-base
  ];
  homepage = "https://github.com/DanielG/ghc-mod";
  description = "Happy Haskell Hacking";
  license = stdenv.lib.licenses.agpl3;
}

ghc-mod.nix

{ mkDerivation, base, binary, bytestring, Cabal, cabal-doctest
, cabal-helper, containers, deepseq, directory, djinn-ghc, doctest
, extra, fclabels, filepath, ghc, ghc-boot, ghc-mod-core, ghc-paths
, ghc-syb-utils, haskell-src-exts, hlint, hspec, monad-control
, monad-journal, mtl, old-time, optparse-applicative, pipes
, process, safe, semigroups, split, stdenv, syb, template-haskell
, temporary, text, time, transformers, transformers-base
, src
}:
mkDerivation {
  pname = "ghc-mod";
  version = "5.9.0.0";
  inherit src;
  doCheck = false;
  isLibrary = true;
  isExecutable = true;
  enableSeparateDataOutput = true;
  enableSharedExecutables = false;
  setupHaskellDepends = [ base Cabal cabal-doctest ];
  libraryHaskellDepends = [
    base binary bytestring cabal-helper containers deepseq directory
    djinn-ghc extra fclabels filepath ghc ghc-boot ghc-mod-core
    ghc-paths ghc-syb-utils haskell-src-exts hlint monad-control
    monad-journal mtl old-time optparse-applicative pipes process safe
    semigroups split syb template-haskell temporary text time
    transformers transformers-base
  ];
  executableHaskellDepends = [
    base binary deepseq directory fclabels filepath ghc ghc-mod-core
    monad-control mtl old-time optparse-applicative process semigroups
    split time
  ];
  testHaskellDepends = [
    base cabal-helper containers directory doctest fclabels filepath
    ghc ghc-boot ghc-mod-core hspec monad-journal mtl process split
    temporary transformers
  ];
  homepage = "https://github.com/DanielG/ghc-mod";
  description = "Happy Haskell Hacking";
  license = stdenv.lib.licenses.agpl3;
}