This being the topic, I'll list the issues I ran into with the new
Data.Map library:
1. The function Map.union is left-biased whereas the old
FiniteMap.unionFM was right-biased. The change seems rather arbitrary.
There are also other changes of this kind, the following two notable
among them:
2. The functions passed to Map.insertWith and Map.insertWithKey expect
their arguments in opposite order from the old FiniteMap.addToFM_C. To
make matters worse, the correct order is not documented so the user is
forced to guess. When I converted my source to use Data.Map instead of
FiniteMap, I guessed wrong and it took me a while to find what was wrong.
3. The Data.Map looks much better than the FiniteMap library, and its
export list is very complete. There are, however, two (or four) more
functions that would be really nice to have in there, as they are
impossible to write efficiently with the functions currently provided:
mapFilter :: (a -> Maybe b) -> Map k a -> Map k b
mapFilter f = map Maybe.fromJust . filter Maybe.isJust . map f
mapPartition :: (a -> Either b c) -> Map k a -> (Map k b, Map k c)
mapPartition f = removeTags . partition isLeft . map f
where isLeft (Either.Left _) = True
isLeft (Either.Right _) = False
removeTags (leftMap, rightMap) = (map (\ (Left x) -> x)
leftMap,
map (\ (Right x) ->
x) rightMap)
For completeness, mapFilterWithKey and mapPartitionWithKey could be
thrown in too.
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