Proposal: Remove Semigroup and Monoid instances for Data.Map, Data.IntMap, Data.HashMap

Evan Laforge qdunkan at
Wed Feb 14 09:08:33 UTC 2018

On Wed, Feb 14, 2018 at 12:49 AM, Akio Takano <tkn.akio at> wrote:
> I'm against this proposal because I think the improvement is, if not
> negative, too small to justify breaking existing code.

I agree for the same reasons.

I also find that unions is the most common.  In my code, I have many
uses of (<>) with the union meaning... it's hard to grep for, but I
guess in the 40-80 range.  Meanwhile, I have a Util.Map.mappend that
also mappends the values, and it's used in 2 places (out of around
140k lines).  It wouldn't be so bad to have to convert them all to
Map.union, but doesn't seem worth the bother either.

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