Correct behaviour of Bounded (Down a)

Oleg Grenrus oleg.grenrus at
Fri Sep 18 14:40:34 UTC 2020

Is it (a bug)?

What about [minBound .. maxBound]. If you change `Bounded`, you need to
change `Enum` too.


- The calls succ maxBound and pred minBound should result in a runtime
- 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
> <mailto:mail at>> 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:
>     Thanks, David.
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