[Haskell-cafe] what does the hidden package error mean?

[Anatoly Yakovenko]

I am trying to build ParseP on the latest ghc, and i am getting this error:

Text/ParserCombinators/ParseP/Interface.hs:26:17:
    Could not find module `Data.ByteString.Char8':
      it is a member of package bytestring-0.9.1.4, which is hidden

what does "hidden" mean?  why does this work in ghci

> import Data.ByteString
> import Data.ByteString.Char8
>

without any problems