ghcWithPackages problem

config.nix

pkgs : {
  packageOverrides = self : {
    ghc741Packages = {
      all = self.haskellPackages_ghc741.ghcWithPackages (Self : [
          self.mtl
          self.QuickCheck
          self.haskellSrcExts
          self.zlib
          self.haskeline
          self.xhtml
          self.hashable
          self.hashtables
          self.syb
          self.blazeBuilder
          self.caseInsensitive
          self.conduit
          self.attempt
          self.base64Bytestring
          self.cereal
      ]);
    };
  };
}

gistfile1.txt

$ sudo nix-env --show-trace -iA nixpkgs_unstable.ghc741Packages
Password:
replacing old `haskell-env-ghc-7.4.1'
installing `haskell-env-ghc-7.4.1'
error: while evaluating the builtin function `derivationStrict':
while instantiating the derivation named `haskell-env-ghc-7.4.1' at `/Users/aristid/.nix-defexpr/channels/nixpkgs_unstable/pkgs/development/compilers/ghc/with-packages.nix:4:3':
while evaluating the derivation attribute `allPackages' at `/Users/aristid/.nix-defexpr/channels/nixpkgs_unstable/pkgs/development/compilers/ghc/with-packages.nix:6:3':
while evaluating the function at `/Users/aristid/.nix-defexpr/channels/nixpkgs_unstable/pkgs/lib/misc.nix:228:22':
while evaluating the function at `/Users/aristid/.nix-defexpr/channels/nixpkgs_unstable/pkgs/lib/misc.nix:162:14':
while evaluating the function at `/Users/aristid/.nix-defexpr/channels/nixpkgs_unstable/pkgs/lib/misc.nix:217:34':
while evaluating the builtin function `isAttrs':
while evaluating the builtin function `head':
attribute `mtl' missing