[Haskell-cafe] packaging modules with internal-only functions

Evan Martin martine at danga.com
Sat Jul 15 22:15:25 EDT 2006

I'm writing an FFI bindings module, and one of the pieces from the
library I want to wrap is their "Error" type.

> module Error where

To the user of the module, I'd like to only expose the nicely wrapped
> data Error = Error String String
> instance Typeable Error where ... -- for throwDyn

But within the module's implementation, I need to share some other,
internal-only functions:
> type ErrorTag = ()
> type ErrorP = Ptr ErrorTag
> withErrorP :: (ErrorP -> IO a) -> IO a
Where withErrorP potentially throwDyns an Error, so it needs the first module.

What is the proper way to divide these up in terms of package exports?
The best options I can figure out are either to split these into
multiple modules, or to have my "Error" module export them and mark
them not to be documented by haddock...

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