Proposal: generalise Monoid's mconcat

[David Feuer]

The theory of mconcat is that it should handle monoids that need to be
summed in some special way. I don't know if anyone actually uses it so,
however. Still, Reid is right that the circular dependency sets a very high
bar.
On Aug 31, 2015 2:47 PM, "Reid Barton" <rwbarton at gmail.com> wrote:

> On Mon, Aug 31, 2015 at 1:54 PM, Fermin Reig <ferminreig at fastmail.fm>
> wrote:
>
>> We could generalise:
>>
>> mconcat:: [a] -> a
>> mconcat = foldr mappend memtpy
>>
>> to:
>>
>> mconcat:: Foldable t => t a -> a
>> mconcat = foldr mappend memtpy
>> -- even
>> -- mconcat = fold
>>
>
> I don't understand the appeal of generalizing the type of a function when
> the generalization already exists; but in this case it's not a viable
> option anyways because mconcat is a class method of Monoid, and the
> definition of the Foldable class already refers to Monoid. Creating a
> circular dependency of Monoid on Foldable would be a headache best avoided.
>
> Regards,
> Reid Barton
>
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