[Haskell-cafe] Announce: EnumMap-0.0.1

John Van Enk vanenkj at gmail.com
Mon Aug 10 14:32:34 EDT 2009

I've been trying to implement EnumMap as a wrapper for IntMap. Here's
the first problem I ran into:

> IntMap.insertWithKey :: (Key -> a -> a -> a) -> Key -> a -> IntMap a -> IntMap a

I'd like to translate this to something like:

> EnumMap.insertWithKey :: Enum k => (Key k -> a -> a -> a) -> Key k -> a -> EnumMap k a -> EnumMap k a

My initial thought was just to make it a normal wrapper:

> EnumMap.insertWithKey f k v m = IntMap.insertWithKey f (unKey k) v (unEnumMap m)

The obvious problem here is the type of `f' expected by the wrapper
function and the internal function. Either we force the wrapper to
take a function that takes an Int as the first parameter, or we
rewrite the logic of insertWithKey to allow us to use the proper (Key
k) type.

I don't see an obvious way around this--am I missing something?

On Sat, Aug 8, 2009 at 4:41 PM, Henning
Thielemann<lemming at henning-thielemann.de> wrote:
> On Sat, 8 Aug 2009, John Van Enk wrote:
>> Hi List,
>> I've uploaded a first version of EnumMap to hackage.
>> EnumMap is a generalization of IntMap that constrains the key to Enum
>> rather than forcing it to be Int. I have no idea what impact this has
>> on performance, but it still passes all the tests that ship with
>> IntMap. (My guess is that performance will be similar/identical unless
>> I've missed something.)
> Could that be implemented as wrapper around IntMap?

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