Proposal: Add conspicuously missing Functor instances for tuples

[amindfv at gmail.com]

If the only uses we can imagine for these instances are
   - Cases where it's not a great design decision
   - Cases where it's used accidentally and results in a silent runtime failure instead of a compile-time error

then I'm a strong -1

Tom

> El 19 ene 2016, a las 15:54, Alois Cochard <alois.cochard at gmail.com> escribió:
> 
> I don't have any use case like that. I'm in favor of this proposal for consistency sake.
> 
> That last part of my comment about usefulness/discouraging usage was about using Functor instance on tuple in general, no matter the arity. 
> 
>> On 19 January 2016 at 21:32, <amindfv at gmail.com> wrote:
>>> El 19 ene 2016, a las 10:24, Alois Cochard <alois.cochard at gmail.com> escribió:
>>> 
>>> +1
>>> 
>>> Agree for consistency, I can also see those instances as being useful in some specific context, even if I agree with Andreas that in general they should be discouraged (especially for newcomers).
>>> 
>> 
>> Can you give us an example where using e.g. the Functor instance for a 5-tuple would be the correct/best design decision?
>> 
>> Tom
>> 
>> 
>>> 
>>>> On 19 January 2016 at 09:20, Herbert Valerio Riedel <hvriedel at gmail.com> wrote:
>>>> On 2016-01-18 at 21:10:07 +0100, David Feuer wrote:
>>>> > For some reason I really can't imagine, it seems the only tuple type
>>>> > with a Functor instance is (,) a. I was astonished to find that
>>>> >
>>>> > fmap (+1) (1,2,3)
>>>> >
>>>> > doesn't work. Since this is *useful*, and there is *only one way to do
>>>> > it*, I propose we add the following:
>>>> >
>>>> > instance Functor ((,,) a b) where
>>>> >   fmap f (a,b,c) = (a,b,f c)
>>>> > instance Functor ((,,,) a b c) where
>>>> >   fmap f (a,b,c,d) = (a,b,c,f d)
>>>> > etc.
>>>> 
>>>> As stated elsewhere in this thread already, there is the issue about
>>>> consistency. Here's a relevant section from the Haskell 2010 report[1]:
>>>> 
>>>> > 6.1.4 Tuples
>>>> >
>>>> > ...
>>>> >
>>>> > However, every Haskell implementation must support tuples up to size
>>>> > 15, together with the instances for Eq, Ord, Bounded, Read, and Show.
>>>> 
>>>> IMO, we either have no `Functor` instances for tuples at all, or we have
>>>> them for all tuples up to size 15. The current situations of having them
>>>> defined only for 2-tuples is inconsistent.
>>>> 
>>>> 
>>>> Cheers,
>>>>   hvr
>>>> 
>>>>  [1]: https://www.haskell.org/onlinereport/haskell2010/haskellch6.html#x13-1210006.1.4
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>>> 
>>> 
>>> 
>>> -- 
>>> Λ\ois
>>> http://twitter.com/aloiscochard
>>> http://github.com/aloiscochard
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> 
> 
> 
> -- 
> Λ\ois
> http://twitter.com/aloiscochard
> http://github.com/aloiscochard
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