[Haskell-cafe] How to derive instance for type without exported constructor?

[Grigory Sarnitskiy]

> {-# OPTIONS_GHC -fglasgow-exts -XGenerics -package lang #-}

Got some problems:

    Could not find module `Generics':
      it is a member of package ghc-6.8.2, which is hidden
Failed, modules loaded: none.

and for ghci test.hs -fglasgow-exts -XGenerics -package lang

ghc-6.8.2: unknown package: lang