Comment 0 for bug 733584

E.g., when trying to compile an application that uses Control.Monad.IO.Class . . .

$ ghc --make -i./src/ src/main.hs -o ./myapp

src/main.hs:6:7:
    Could not find module `Control.Monad.IO.Class':
      It is a member of the hidden package `transformers-0.2.1.0'.
      Use -v to see a list of the files searched for.

I can, of course, specify the package manually when compiling (using the -package flag of ghc), or I can use the ghc-pkg utility to unhide the package (ghc-pkg expose transformers), but why is it hidden by default?