Sean Leather wrote:
I have a module A that re-exports module B, and module B contains only
class instances. Since I'm using -Wall, I get this warning about module B exporting nothing. Is there a way to disable this particular warning, since it is unnecessary in this case? No mailing list messages or GHC documentation has told me what to do.
Well, the warning is right that you don't need to re-export module B: instances are implicitly exported. So you could just remove the export of "module B", unless there's a reason to export it (such as, you might add some exported functions or data types to it later)
Hmm, the disappointing result of removing module B from the export list is that now it doesn't show up in the Haddock-generated documentation for module A. Not that there was anything specific in B to document, because it's only instances. But I do want the user to know that importing A also imports B. Sigh... I suppose there's CPP if I really want it.
You could put a link to the module in the intro-documentation that comes before the export list, possibly in a sentence saying e.g. "deliberately exports instances from @module B@" (except I've forgotten Haddock syntax and might have used it wrong there :-) It's an interesting use-case though. I wonder if Haddock should automatically provide links to all instances exported from the module that are either (1) instances for datatypes or classes exported by the module, or (2) orphan (i.e. not defined in the same module as either the class or the datatype). (It would be too tedious to list *all* exported instances, but luckily it's not necessary for completeness.) -Isaac