On Mon, Nov 28, 2011 at 2:28 PM, Milan Straka
1) `{Map,Set}.deleteMin empty` return `empty` `{IntMap,IntSet}.deleteMin empty` trigger `error "Cannot delete in empty..."`
Solutions: (a) make `{Map,Set}.deleteMin empty` throw error (b) make `{IntMap,IntSet}.deleteMin empty` return empty
I vote for (b), because (a) could cause unexpected runtime errors. Additionally, I expect very little programs depend on `{IntMap,IntSet}.deleteMin empty` causing runtime error.
+1 for (b) as well.
2) `Map.deleteFind{Min,Max}` has type `Map k a -> ((k,a),Map k a)` `IntMap.deleteFind{Min,Max}` has type `IntMap a -> (a, IntMap a)`
Solutions: (a) make the Map variant return only values (b) make the IntMap variant return both key and value
I vote for (b), because it generalizes the original functionality.
+1 for (b) as well.
3) `Map.update{Min,Max}` is given a function of type `(a -> Maybe a)` `Map.update{Min,Max}WithKey` is given a function of type `(key -> a -> Maybe a)` `IntMap.update{Min,Max}` is given a function of type `(a -> a)` `IntMap.update{Min,Max}WithKey` is given a function of type `(key -> a -> a)`
Solutions: (a) the Map variants would get a function of type `[key -> ] a -> a` (b) the IntMap variants would get a function of type `[key -> ] a -> Maybe a`
I vote for (b), because it generalizes the original functionality.
+1 for (b) as well.
4) The functions `mapKeys :: Ord k2 => (k1->k2) -> Map k1 a -> Map k2 a` `mapKeysWith :: Ord k2 => (a -> a -> a) -> (k1->k2) -> Map k1 a -> Map k2 a` `mapKeysMonotonic :: (k1->k2) -> Map k1 a -> Map k2 a` have no IntMap correspondents. Both `mapKeys` and `mapKeysWith` can be defined by the user without loss of performance.
Solutions: (a) deprecate the `mapKeys*` methods from Map (b) add the `mapKeys*` methods to IntMap.
I vote for (a). These methods are all trivial compositions and all but all mapKeysMonotonic are defined as such. For mapKeysMonotonic, a trivial composition with the same asymptotic complexity exists. Also, if these were added to IntMap, none of them would have better performance then user-defined methods.
-1 for (a). I'd rather write 'M.mapKeys f m' than 'M.fromList $ map (\(k,x) -> (f k, x)) $ M.toList m'. +1 for (b).
5) `toDescList` exists in Map, but not in IntMap, Set or IntSet.
Solutions: (a) deprecate `Map.toDescList` (b) add `toDescList` to IntMap. In this case, we should consider adding it also to Set and IntSet.
I have no strong opinion here. The `toDescList` can be trivially expressed as left fold. But it is currently a subject to list fusion. To vote for (a).
-1 for (a). +1 for (b).
Several other changes follow:
6) Result of discussion around http://hackage.haskell.org/trac/ghc/ticket/5242 Add `Map.fromSet :: (key -> a) -> Set key -> Map key a` `IntMap.fromSet :: (Int -> a) -> IntSet -> IntMap a` The implementation would exploit same structure of map and set (leave the shape of the original tree/trie, just adding values).
Cons: fromSet is a trivial composition: fromSet f = Map.fromDistinctAscList . map (\k -> (k, f k)) . Set.toAscList This can be defined by the user and is asymptotically optimal. Pro: performance. Also the performance of keysSet would improve, if the map can use data constructors of set.
I vote for adding these methods.
+1
7) Improve the generality of intersectionWith. Currently the Map and IntMap define intersectionWith :: Ord k => (a -> b -> c) -> Map k a -> Map k b -> Map k c intersectionWithKey :: Ord k => (k -> a -> b -> c) -> Map k a -> Map k b -> Map k c
But the combining function is not general enough. Consider two IntMaps storing hashable elements as (hash(element), element). When intersecting elements with the same hash, the intersection can be empty.
I propose to change the type of these methods to intersectionWith :: Ord k => (a -> b -> Maybe c) -> Map k a -> Map k b -> Map k c intersectionWithKey :: Ord k => (k -> a -> b -> Maybe c) -> Map k a -> Map k b -> Map k c (and appropriately for IntMap).
Note that the combining function of differenceWith already has type `(a -> b -> Maybe a)`.
I have no strong opinions on this =). Thanks! -- Felipe.