Edward Kmett ekmett at
Tue Mar 31 10:41:27 UTC 2015

We deliberately took no more symbols than we needed in 7.10 from Prelude as
part of the Foldable/Traversable Proposal. There are multiple combinators
in Data.Foldable and Data.Traversable that we do not export. traverse_ is
one of them as, strictly speaking, traverse_ was a symbol we didn't have to

If we had would anybody have complained any more loudly? Not sure... but it
was a deliberate choice to not bring in any symbols into Prelude that
weren't already there that weren't part of the definition of a class or
needed to define instances that already existed.


On Mon, Mar 30, 2015 at 11:33 PM, Fumiaki Kinoshita <fumiexcel at>

> Well, I see. It'd be nice.
> That aside, the absence of traverse_ doesn't seem to be intended (even the
> documentation for mapM_ says "mapM_ is just traverse_"!)
> 2015-03-30 16:54 GMT+09:00 Herbert Valerio Riedel <hvr at>:
>> On 2015-03-30 at 07:05:56 +0200, Fumiaki Kinoshita wrote:
>> [...]
>> > I found out that (<>) (in Data.Monoid) is missing, also. It would be
>> nice
>> > to reexamine Prelude to export things we want to export.
>> Fwiw, (<>) was actually left-out as it wasn't required (it's just a an
>> alias for `mappend`), *and* to keep our options open (or at least not
>> make it more difficult) in terms of possible migration-plans available
>> for the case we'd be moving 'Semigroup' to base/Prelude at some point in
>> the future.
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