// This my haskell dev env (please note I don't use stack)
with import <nixpkgs> {};
{
  sdlEnv = stdenv.mkDerivation {
    name = "haskell";
    shellHook = ''
      export NIX_LABEL="haskell"
    '';
    buildInputs = [
      ghc cabal-install cabal2nix stack
    ];
  };
}


// Here is the result of cabal2nix
{ nixpkgs ? import <nixpkgs> {}, compiler ? "default", doBenchmark ? false }:

let

  inherit (nixpkgs) pkgs;

  f = { mkDerivation, base, containers, hedgehog, hspec
      , postgresql-simple, stdenv, text
      }:
      mkDerivation {
        pname = "simity";
        version = "0.0.0.0";
        src = ./.;
        isLibrary = true;
        isExecutable = true;
        libraryHaskellDepends = [ base containers postgresql-simple text ];
        executableHaskellDepends = [ base containers postgresql-simple ];
        testHaskellDepends = [ base containers hedgehog hspec text ];
        doHaddock = false;
        license = "LicenseRef-PublicDomain";
      };

  haskellPackages = if compiler == "default"
                       then pkgs.haskellPackages
                       else pkgs.haskell.packages.${compiler};

  variant = if doBenchmark then pkgs.haskell.lib.doBenchmark else pkgs.lib.id;

  drv = variant (haskellPackages.callPackage f {});

in

  if pkgs.lib.inNixShell then drv.env else drv


// Then i do `nix-shell . --command fish` with the file above as `default.nix`