foldr on ElemsView is defined as such:
foldr f i (ElemsView c) = foldr (f . snd) i c
so, for example:
getElementList = toList . ElemViews
When I designed this code (some years ago), I didn't like the "fold" of Map to have the type:
fold :: (a -> b -> b) -> b -> Map k a -> b
This just doesn't make sense if we see maps as a collection of (key, value) pairs. (Indeed, toList :: Map k a -> [(k, a)]) In order to be consistent, but to provide an easy way to migrate to the new collection classes I was designing, I provided the ElemViews/KeyViews to "switch" to the former behaviour on a case by case basis. This also allows for definining optimized versions of foldr, etc. for each types that supports "Views", but this was tedious, so I never did it. GHC "RULE" pragma is probably better suited to the purpose anyway. As for the lack of documentation, everyone is very welcome to contribute ;) Cheers, JP.