deps don't get picked up by nix-shell

shell.nix

{ pkgs ? (import <nixpkgs> {}),
  haskellPackages ? (import <nixpkgs> { }).haskellPackages,
  stdenv ? (import <nixpkgs> { }).stdenv }:
let
  inherit (haskellPackages)
    base bytestring heist lens MonadCatchIO-transformers mtl snap
    snap-core snap-loader-static snap-server text time xmlhtml
    snaplet-sass snaplet-acid-state acid-state safecopy uuid
    containers aeson base64-bytestring directory Rasterific
    JuicyPixels haskell-qrencode regex-tdfa shell-conduit
    conduit-extra resourcet;
in with haskellPackages; mkDerivation {
  pname = "package-name";
  version = "0.1.0.0";
  src = ./.;
  isLibrary = false;
  isExecutable = true;
  buildTools = [ pkgs.git cabal-install ];
  buildDepends = [
    base bytestring heist lens MonadCatchIO-transformers mtl snap
    snap-core snap-loader-static snap-server text time xmlhtml
    snaplet-sass snaplet-acid-state acid-state safecopy uuid
    containers aeson base64-bytestring directory Rasterific
    JuicyPixels diagrams diagrams-rasterific haskell-qrencode
    regex-tdfa shell-conduit conduit-extra resourcet
  ];
  license = stdenv.lib.licenses.unfree;
}