[Haskell-cafe] Data.Map traversal.

[Serguey Zefirov]

I found that I often need predecessor and successor of some key in 
Data.Map.Map. Just like that:

predKey, succKey :: Ord k => Data.Map.Map k a -> k -> Maybe k
predKeyElem, succKeyElem :: Ord k => Data.Map.Map k a -> k -> Maybe (k,a)

Data.Map has operations like that on key indexes, but it is slightly 
unnatural to work with three entities (index, key and element) where two 
suffices.

So I propose to include those operations into next version of Data.Map.
 
If anyone could point me in the right direction I could do any necessary 
modifications myself (just because I need it).