On Feb 6, 2008 10:36 AM, Henning Thielemann
type SomethingWithKV k a = KV {getKV :: (k, a)} instance Buildable (Map k a) (SomethingWithKV k a) where empty = Map.empty insert s m = uncurry Map.insert (getKV s) m
I have done this before -- it's very convenient, and I think makes the code that uses empty and insert more robust, and easier to read.
But why do you want to have the special type SomethingWithKV, but not MapSomething ?
Do you mean a map that maps SomethingWithKV to whatever, instead of k to v? My point is that if you add the functional dependency, you can't write instances for types which wrap what you're really interested in. You have to manually unwrap those types everywhere they interact with a map. This is tedious and error-prone. Being able to write such instances is useful, I think, though not always clearer in all cases. -- Denis