Re: Proposal: Non-allocating way to iterate over a Data.Map: traverseWithKey_

Hi Ryan,

-----Original message----- From: Ryan Newton Sent: 30 Jul 2013, 09:35

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(!) adjust adjustWithKey alter delete empty findWithDefault foldl foldl' foldlWithKey foldlWithKey' foldr foldr' foldrWithKey foldrWithKey' insert insertLookupWithKey insertWith insertWithKey lookup map mapAccum mapAccumRWithKey mapAccumWithKey mapMaybe mapMaybeWithKey mapWithKey member notMember toList update updateLookupWithKey updateWithKey

So then this becomes a recommendation for the implementation strategy then right? (e.g. within containers) Users probably still want a rich set of variants, and they need to be packaged somewhere. But it seems like there's an argument that deriving these from a small core helps to ensure that there are no bugs.

Yet that sounds like a battle for another day. On the topic of this proposal -- since Shachaf doesn't object, would you (Johan / Milan) mind merging this patch?

I would like to postpone merging for a bit and spend more time investigating the issue. I want to investigate why exactly foldrWithKey (\k a b -> f k a *> b) (pure ()) does not work as I would expect it not to allocate. I am not convinced that traverseWithKey_ is a good addition to the API because my original thought was "this is just a fold". The API of containers has tendency to grow, so I am careful about adding functions that can be expressed easily using existing ones. Of course, ability to iterate effectively over the elements of the containers definitely IS useful, so if I am unable to make the fold work (or GHC optimizer cannot do it at present), I will merge it. Cheers, Milan