Bikeshedding: Would it be better to put the definition for +> (or better yet <>) in the dictionary for Monoid with a circular definition for mappend? That way new code defining Monoid instances can avoid ever having to even mention mappend. I'm ok with it either way. I admit adding it to the dictionary might add dictionary passing overhead and risk inconsistent definitions of <> and mappend.

-Edward Kmett

On Tue, Jun 30, 2009 at 5:37 PM, Bryan O'Sullivan <bos@serpentine.com> wrote:

Ticket: http://hackage.haskell.org/trac/ghc/ticket/3339

From the ticket:

This proposal was, I think, originally suggested by Jules Bean. The idea is to add two functions to the Data.Monoid module, (+>) and (<+), corresponding to different uses of mappend. These should not be methods of the Monoid typeclass, but top-level functions.

I hope (but slightly doubt) that the visual nature of the two operators might help to counter the thought that monoids are just for gluing things together.
(+>) :: (Monoid a) => a -> a -> a
a +> b = a `mappend` b


(<+) :: (Monoid a) => a -> a -> a
a <+ b = b `mappend` a

infixl 4 +>
infixl 4 <+
Proposed deadline: two weeks.

If this looks reasonable, I'll attach darcs patches.

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