Re: Correct behaviour of Bounded (Down a)

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 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 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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