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.
So, I tried to do the above with CPP, and I can't get Haddock to recognize that it should list this. Here's what it looks like:
module A (
module Z,
#ifdef __HADDOCK__
module B
#endif
) where ...
I added "extensions: CPP" to the .cabal file as I saw instructed in some Cabal thread from long ago. Building works such that I don't get the warning, but "cabal haddock" just acts as if it doesn't recognize __HADDOCK__. Assuming I'm not doing anything wrong, this might be a Cabal problem.
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 :-)
Yep, that is an option. I noticed it in the documentation for another package, the name of which escapes me right now.
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.)
Yeah, I think instances should be documented in general. But, I agree with Ross in the previous thread, that's a different story.
Sean