Correct behaviour of Bounded (Down a)

[Carter Schonwald]

Indeed. Enum as it’s currently defined is totally broken and actively a bad
interface :)

On Fri, Sep 18, 2020 at 11:04 AM David Feuer <david.feuer at gmail.com> wrote:

> We should add an Ord constraint to Enum and Bounded. The more constraints
> we add to Enum, the fewer instances we will have and the sooner my ultimate
> goal of removing it altogether will be achieved. Mwahahahaha!
>
> On Fri, Sep 18, 2020, 10:41 AM Oleg Grenrus <oleg.grenrus at iki.fi> wrote:
>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>> Is it (a bug)?
>>
>>
>>
>>
>>
>> What about [minBound .. maxBound]. If you change `Bounded`, you
>>
>> need to change `Enum` too.
>>
>>
>>
>>
>>
>> From
>>
>>
>> https://hackage.haskell.org/package/base-4.14.0.0/docs/GHC-Enum.html#t:Enum
>>
>>
>>
>>
>>
>> - The calls succ maxBound and pred minBound should result in a
>>
>> runtime error.
>>
>>
>> - enumFrom and enumFromThen should be defined with an implicit
>>
>> bound
>>
>>
>> The `min` and `max` in `minBound/maxBound` are related to `succ`,
>>
>> `pred`, not to `compare`. If you argue against, then we should add
>>
>> `Ord` super-class to `Enum` (and `Bounded`).
>>
>>
>>
>>
>> - Oleg
>>
>>
>>
>>
>> On 18.9.2020 16.54, Carter Schonwald
>>
>> wrote:
>>
>>
>>
>>
>>
>>
>>
>>
>> Def a bug! Plz at myself and the core libraries
>>
>> handle for code review plz.
>>
>>
>>
>>
>>
>>
>>
>> This sounds kinda related to an MR that has
>>
>> languished too long regarding the behavior of Down on Ord1,
>>
>> which I think is related??? (I tried to arbitrate / layout
>>
>> possible answers for the related issue in the associated mr, but
>>
>> none of the clc members have engaged in the design space
>>
>> challenge)
>>
>>
>>
>>
>>
>>
>>
>> On Fri, Sep 18, 2020 at 7:44
>>
>> AM David Beacham <mail at dbeacham.co.uk> wrote:
>>
>>
>>
>>
>>
>>>
>>>
>>>
>>> Hi all,
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> The current instance for `Bounded a => Bounded
>>>
>>> (Down a)` derives the `minBound` and `maxBound` exactly
>>>
>>> as they are for the underlying type `a` where I think
>>>
>>> they should be flipped to respect the flipped ordering
>>>
>>> of `Down a`?
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> I have a feeling this has been come up in some other
>>>
>>> context/list before but I couldn't find a reference to
>>>
>>> it when searching - so sorry if this is a duplicate.
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> I've got a corresponding MR here:
>>> https://gitlab.haskell.org/ghc/ghc/-/merge_requests/4081
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> Thanks, David.
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
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>>>
>>>
>>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
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>
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