Andrew Wagner wrote:
So, in writing my chess engine, I've been trying to maintain 2 Map objects. One maps squares on the board to Ints, the other maps Ints to actual Pieces. It occurred to me that it would be useful to explicitly have a Bi-directional Map, which does the maintenance of keeping the Maps synchronized behind the scenes. Thus, Bimap was born! I've taken the API for Data.Map (which you can find at ), and cannibalized it for Bimap. The new API is at http://hpaste.org/2344 . The idea is that if you have a Bimap k a, and you want to treat the k's as keys, and use a function like Data.Map.foo, it will be called Data.Map.left_foo in Bimap. And if they want to do the same thing, but using the a's as keys, then they simply use right_foo. The metaphor is that we can view it as a Map in 2 directions, manipulating it from the left (on the k's), or from the right (on the a's).
Is this useful? Is there a better way? Is the API too big, and if so, how can it be pared down?
IMHO, the API is too big and not beautiful enough. How about a function flip :: Bimap a b -> Bimap b a that interchanges the role of keys and values? Or maybe keep every functions symmetric in a and b , like in update :: ((a,b) -> Maybe (a,b)) -> Either a b -> Bimap a b -> Bimap a b The changer functions take pairs and the search key to look for is Either a b . But most of the map functions (including update above) probably won't work anyway, what should left_insertWith (\new old -> new) 'a' 1 (fromList [('a',2),('b',1)]) do? I can't yield fromList [('a',1),('b',1)] since 1 has two keys now. Regards, apfelmus