[Proposal] Add default implementation of mappend/mempty in terms of mconcat

[Henning Thielemann]

Am 27.01.2014 13:23, schrieb Joachim Breitner:
> Hi,
>
> Am Montag, den 27.01.2014, 11:42 +0100 schrieb Sjoerd Visscher:
>> This seems rather pointless; I’m having trouble coming up with an
>> example where mconcat would be easier or more elegant to implement. Do
>> you have an example?
>
> maybe cases where you implement mconcat for performance reasons anyways
> (but are there good examples for that?),

I think it is useful to define a custom mconcat in cases where it 
matters whether it is a left or a right fold.

 > and then you don’t want to be bothered with the simple cases....