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

Wed May 21 22:31:47 UTC 2014

> Why not defining a class in xml-conduit then?

This is hardly something that affects just one or two packages.

http://packdeps.haskellers.com/reverse/data-default

There seems to be 232 packages using Data-Default.

Cheers

2014-05-21 19:46 GMT+01:00 Michael Snoyman <michael at snoyman.com>:

> I honestly don't feel very strongly about usage of Default. What I've
> found it useful for is a very narrow category: a function which takes a
> configuration parameter that users likely never want to modify. For
> example: xml-conduit has various parsing and rendering settings, but most
> use cases are good with the default. There's a cognitive overhead for a
> user to remember the default parameter name (is it defaultXMLSettings?
> defaultXmlSettings? defParseSettings?).
>
>
> On Wed, May 21, 2014 at 7:11 PM, Adam Bergmark <adam at bergmark.nl> wrote:
>
>> As is, I don't find data-default to be useful, and decided to move away
>> from it in fay for a number of reasons:
>>
>> * You cannot add arguments to it because of the existing Default<http://hackage.haskell.org/package/data-default-0.5.3/docs/Data-Default.html#t:Default> r
>> => Default<http://hackage.haskell.org/package/data-default-0.5.3/docs/Data-Default.html#t:Default> (e
>> -> r)  instance or run it in e.g. IO (via Chris Done)
>> * The previous point means it's likely you'll have to scrap your instance
>> at some point instead of just changing a type
>> * You need to either re-export def or users need to depend on
>> data-default themselves. Even if it was in base (but not in Prelude) they
>> would need to add an additional import
>> * The semantics needs to be defined for each instance
>> * I don't see any use case for abstracting over different instances of
>> Default
>> * I think it's useful to be explicit about the "default" value you are
>> using. I'm unlikely to use `def' over `Set.empty'. Code is read more often
>> than it's written.
>>
>> I think Empty sounds like a better name. Some things have a clear "empty"
>> value that will never change. I don't object strongly to using
>> Empty/Default for these.
>>
>>
>>
>> On Wed, May 21, 2014 at 5:37 PM, João Cristóvão <jmacristovao at gmail.com>wrote:
>>
>>> I stand corrected, he actually posted something on github this month.
>>>
>>> Lucas, what would you think about merging generics support into
>>> Data.Default?
>>>
>>> João
>>>
>>>
>>> 2014-05-21 16:31 GMT+01:00 João Cristóvão <jmacristovao at gmail.com>:
>>>
>>> I definitely see your point, and have suffered that myself, of course.
>>>>
>>>> I just guess I did not want to get with the trouble of taking ownership
>>>> of a package, after trying to contact Lucas Mai on February this year, with
>>>> no response.
>>>> His github repository shows no activity since October last year.
>>>> https://github.com/mauke
>>>>
>>>> But I do guess it is the right thing to do: if anyone knows Lucas and
>>>> can contact him, to see if he stills wishes to maintain the package, I
>>>> would very much appreciate that (I've also included the .cabal listed email
>>>> in this conversation).
>>>> If he is not interested or does not respond within a reasonable time
>>>> frame, I propose myself as maintainer of the package (and will gladly
>>>> accept suggestions).
>>>>
>>>> Cheers
>>>> João
>>>>
>>>>
>>>> 2014-05-21 16:18 GMT+01:00 Michael Snoyman <michael at snoyman.com>:
>>>>
>>>> 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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>>>>>>>>
>>>>>>>>
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>>>>>>>>
>>>>>>>
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>>>>>>
>>>>>
>>>>
>>>
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>>
>
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