A more useful Monoid instance for Data.Map

[Ben Gamari]

Roman Cheplyaka <roma at ro-che.info> writes:

snip.
>
> So maybe we should push the change that was discussed in another thread
> to move Semigroup into base, and only then change this instance.
>
Are you proposing that (.++.) /= mappend?

I think this sort of inconsistency would be a mistake, especially given
the evidence that suggests that relatively little code will be affected
by the change in mappend's semantics.

Cheers,

- Ben