I'd hazard that if you went 'containers' and looked at what instances were implemented, that would give you a good idea. :^) (For example, if you look at Data.MAp, it has NFData, Typeable2 and Data instances.) Edward Excerpts from Christoph Breitkopf's message of Thu Dec 08 11:12:06 -0500 2011:
Hello,
I'm in the process of implementing a container data type, and wonder what class instances are generally considered necessary. E.g. is it ok to start out with a Show that's adequate for debugging, or is it a 'must' to include instances of everything possible (Eq, Ord if possible, Read, Show, Functor, ...).
And what about the more experimental things? Say, DeepSeq, Typeable, Data? I'd like to keep this simple at start, and I've admittedly not followed recent developments in Haskell-land (recent meaning the last 10 years or so. I _do_ know about hierachical modules ;-) ).
OTOH, if not having such instances makes it impossible to do things the modern way, I'd probably take the time to implement (and maybe understand) them.
Thanks,
Chris