[Haskell-cafe] MonoidHashMap?

[Michael Snoyman]

I've definitely wanted it in the past, and have even implemented limited
versions of it before. I'd be open to adding it to Data.Containers in
mono-traversable[1].

[1]
http://www.stackage.org/haddock/nightly-2015-01-20/mono-traversable-0.7.0/Data-Containers.html

On Tue Jan 20 2015 at 4:34:00 AM Konstantine Rybnikov <k-bx at k-bx.com> wrote:

> Hi!
>
> I'm working with a lot of HashMap's and it's very frustrating how many
> times I've "lost" my data because of usage of either a Monoid instance of a
> HashMap (which is defined as H.union, which, upon collision, takes value
> from first hm and discards from second), or just using fromList in the
> wrong place. Whereas the data I'm working is is mostly defined as (Monoid v
> => HashMap k v), so what I need "by default" is actually something like
> `H.unionWith (<>)`.
>
> What I was wondering is this: is something like MonoidHashMap is desired
> to be in unordered-containers, or is this use-case only popular in my
> programs? I'm asking because I have a feeling that this thing might be
> useful quite a lot for others also. If not -- sorry for bothering :)
>
> Cheers!
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