Proposal #3339: Add (+>) as a synonym for mappend

Edward Kmett ekmett at
Sun Aug 14 22:24:17 CEST 2011

On Sun, Aug 14, 2011 at 4:20 PM, Yitzchak Gale <gale at> wrote:

> I think I've made my position clear, so I'm going to stop
> beating the drum and giving everyone a headache.
> But for a different reason, I feel I do need to respond to
> one more comment:
> Johan Tibell wrote:
> > We're not going to stop changing base because someone added an
> > operator with the same name as we'd like to use in some package on
> > Hackage.
> That is really not fair to Edward. He is not just "someone" - he
> is one of today's leading contributors to Haskell's ecosystem,
> both in quantity and in quality. When he makes a contribution
> directed at a general audience, like this one, it is intuitive, practical,
> performant, elegant, carefully considered, and based on deep
> theoretical harmony.
> Edward did not just add "an operator with the same name". He implemented
> this ticket, the right way. It's done. You can already use <> today - just
> say "import Data.Semigroup ((<>))". If you want to put that in base, go
> right ahead.
> Please don't imply that I am against making changes to base
> in general. The reason we came to this situation in the first place
> is that the original proposal languished for so long. At least
> this time, whatever we decide will be implemented right away. :)
> As I type this, Edward himself has come out in favor of the
> original proposal, thus breaking all code based on his own
> package. So I guess that settles it.

Thank you for the support. In a perfect world, I would like to have the (<>)
operator be in semigroup and the monoid class just lose mappend, being just
mempty. This would let us fix the broken monoid instance for Maybe, dropping
the need for Option in the semigroups package and let us introduce nice Min
and Max semigroups.

But I could live with the (<>) = mappend compromise. I'm sure it somehow
makes someone somewhere happier than doing the right thing.


> Thanks,
> Yitz
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