Proposal: add full complement of support for decreasing things in Data.Map

Nickolay Kudasov nickolay.kudasov at
Thu May 19 14:48:22 UTC 2016

I see, thank you for clarification!

Kind regards,

On Thu, 19 May 2016 at 17:44 David Feuer <david.feuer at> wrote:

> Yes, but no. Once you do that, the whole map is Down. Aside from the
> inconvenience factor, such a map can't be combined with one in the usual
> order using union, intersection, etc. We could add conversion functions,
> but they'd copy the whole structure and really only be special cases of the
> hypothetical mapKeysDescending.
> On May 19, 2016 10:40 AM, "Nickolay Kudasov" <nickolay.kudasov at>
> wrote:
>> Hi David,
>> Can't this be done simply by using Data.Ord.Down wrapper for the keys?
>> Kind regards,
>> Nick
>> On Thu, 19 May 2016 at 17:00 David Feuer <david.feuer at> wrote:
>>> Data.Map offers functions to convert from ascending lists to maps, and
>>> also offers a function to map an increasing function over the keys of a
>>> map. Equivalents for descending lists and decreasing functions are missing.
>>> I think we should add them. Any objections?
>>> _______________________________________________
>>> Libraries mailing list
>>> Libraries at
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