GHC refuses to export qualified modules

Question

I want to write a module which re-exports some module it had imported qualified. Something like this:

module Foo.A
  ( module Foo.B
  , module Foo.C
  ) where
im         


        

Answer 1

This limitation is also a convenience when the importing module is meant to re-declare some names in the imported module, based on declarations of a qualified import. For instance:

module MyPrelude (succ, module Prelude) where

import qualified Prelude as P (succ)
import Prelude hiding (succ)

succ :: ...
succ = ... P.succ ...

this idiom would be really hard to express without a lot of verbosity otherwise. Also, ask your self "would this make sense without hierarchical modules?". If not, then this is very ghc specific, and what is actually going on when referencing a hierarchical module name from an expression is not hierarchical at all.

As to why you are able to reexport individual symbols qualified by some module name you did not import, that seems like a kludge to get heirarchical modules to work heirachically in ghc. Gaining Foo.B qualified symbols when importing Foo.A is magical, and I think its because The name Foo is no more an actual heirachical ancestor than Foo.A, but the intended use of exporting things with alternate qualification is in cases where its used from Foo. I don't think this behavior makes sense at all without GHC extensions, so I am going to take a wild guess that its GHC specific.