I have a dilemma about library building that I'm expect comes up for other people as well. I'm working on a library that includes a Cofunctor instance. I'd love to import whatever standard module has the Cofunctor class, and maybe use some Cofunctor combinators. But, alas, I haven't found such a thing, and I'm wondering what to do. If I keep my Cofunctor class in my own library, the generality does no good to me or anyone else. I certainly wouldn't expect someone to install my library just to get Cofunctor. Just as I wouldn't want a dependency on some other mostly-irrelevant library just to get Cofunctor. Another option is for me to make a tiny Cofunctor package with just a single class declaration, and make my library dependent on it. I guess that's the cleanest way and is what I'm leaning toward. And maybe it could grow into a more useful Cofunctor library with the addition of functions on generic Cofunctor types. Does anyone have useful functionality to go into a Cofunctor module (beyond the class declaration)? Comments, advice, brainstorming most welcome. Cheers, - Conal