Command

$ nix-instantiate haskell-rethinkdb.nix --indirect --add-root $PWD/shell.drv --show-trace

default.nix

{ mkDerivation, aeson, attoparsec, base, base64-bytestring, binary
, bytestring, containers, data-default, doctest, mtl, network
, scientific, stdenv, text, time, unordered-containers, utf8-string
, vector
}:
mkDerivation {
  pname = "rethinkdb";
  version = "2.0.0.0";
  src = ./.;
  isLibrary = true;
  isExecutable = true;
  libraryHaskellDepends = [
    aeson base base64-bytestring binary bytestring containers
    data-default mtl network scientific text time unordered-containers
    utf8-string vector
  ];
  executableHaskellDepends = [ attoparsec base text ];
  testHaskellDepends = [ base doctest ];
  homepage = "http://github.com/atnnn/haskell-rethinkdb";
  description = "A driver for RethinkDB 2.0";
  license = stdenv.lib.licenses.asl20;
}

haskell-rethinkdb.nix

let
  pkgs = import <nixpkgs> {};
  stdenv = pkgs.stdenv;
  haskellPackages = pkgs.haskellPackages.override {
    overrides = self: super: {
      haskell-rethinkdb = pkgs.haskell.lib.dontCheck (self.callPackage ./default.nix {});
    };
  };
  inputs = [
      haskellPackages.ghc-mod
      haskellPackages.cabal-install
  ];
in rec {
  haskellRethinkDBEnv = stdenv.lib.overrideDerivation haskellPackages.haskell-rethinkdb.env (old: {
    name = "haskell-rethinkdb-env";

    # Append our inputs to the old build inputs
    buildInputs = old.buildInputs ++ inputs;
    NIX_MYENV_NAME = "haskell-rethinkdb";
    shellHook = ''
      source ~/.bash_prompt

      # Run the old shell hook of the haskell environment
      ${old.shellHook}
    '';
  });
}

shell.nix

let
  pkgs = import <nixpkgs> {};

  haskellPackages = pkgs.haskellPackages.override {
    overrides = self: super: {
      haskell-rethinkdb = self.callPackage ./. {};
    };
  };

in haskellPackages.haskell-rethinkdb.env