data-default WAS: [containers] Proposal: Change to the Data.Map Monoid

[Michael Snoyman]

Starting a new thread to continuing discussing this (I should have done so
in the first place).

Here's the problem: a class like Default is most useful if everyone's using
the same class. The reason is that multiple libraries are all free to
reexport the `def` symbol, and they'll all refer to the same identifier. If
multiple `def`s exist, then this doesn't work, you need to be careful about
*which* `def` you're using, and you may as well just export a default value
under its own unique name.

I think data-default-generics is overall an improvement on data-default,
but the very nature of a fork here makes both packages less useful. I'd
much rather that data-default simply merged in data-default-generics.


On Wed, May 21, 2014 at 6:12 PM, João Cristóvão <jmacristovao at gmail.com>wrote:

> Sorry for continuing the off-topic, and for promoting a package of mine:
>
> If you only need the class definition,
> http://hackage.haskell.org/package/data-default-class is a better choice,
> with no dependencies.
>
> If you prefer a single package with all the dependencies (and with
> additional generics support), my own fork might be useful:
> http://hackage.haskell.org/package/data-default-generics
>
> Although I mirrored the original package dependencies, many of which might
> actually be unnecessary... (given the generics implementation).
>
> Cheers
>
>
> 2014-05-21 15:59 GMT+01:00 Michael Snoyman <michael at snoyman.com>:
>
> At the risk of veering terribly off-topic... the splitting of data-default
>> into all of those packages caused me a bunch of dependency headaches, most
>> of which I still don't fully comprehend. I miss the good ol' days of a
>> single package.
>>
>>
>> On Wed, May 21, 2014 at 5:53 PM, Edward Kmett <ekmett at gmail.com> wrote:
>>
>>> I find myself rather hesitant to recommend that instantiation of the
>>> idea ever since it exploded into a half-dozen packages full of orphan
>>> instances, but yes.
>>>
>>> -Edward
>>>
>>>
>>> On Wed, May 21, 2014 at 6:38 AM, Herbert Valerio Riedel <hvr at gnu.org>wrote:
>>>
>>>> On 2014-05-21 at 00:23:44 +0200, Andreas Abel wrote:
>>>> >>> _Lots_ of users initialize empty maps with mempty
>>>> >
>>>> > Well, this is another issue, empty should be overloaded via
>>>> >
>>>> > class Empty a where
>>>> >   empty :: a
>>>>
>>>> Btw, isn't this what
>>>>
>>>>   http://hackage.haskell.org/package/data-default
>>>>
>>>> provides?
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