[Haskell-cafe] how to link to external documentation with haddock ?

Hi, When generating haddock documention (I use runhaskell Setup.lhs haddock), haddock warns me : "could not find link destinations for:" and lists for instance GHC.Show.Show or Data.Either.Either. Is it possible to instruct Haddock to links against http://www.haskell.org/ghc/docs/latest/html/libraries/ for those unfound destinations ? Thanks, Thu