<div dir="ltr"><div>That is a good spot - I had wondered if the minBound/maxBound changes would affect other classes but had missed Enum.</div><div><br></div><div>I wouldn't be surprised that `Down a` had a reversed enumeration despite the `Ord`/`Enum` separation.</div><div><br></div><div><div>Looking at the `Bounded` docs</div></div><div><div><br></div><div>> The Bounded class is used to name the upper and lower limits of a type. Ord is not a superclass of Bounded since types that are not totally ordered may also have upper and lower bounds.</div><div><br></div><div>does suggest that flipping minBound and maxBound is correct? That would then require `Enum a => Enum (Down a)` should also be flipped given the way it interacts with `Bounded`?</div></div><div><br></div><div>I think the instance is achievable by</div><div><br></div><div>1. flipping pred/succ</div><div>2. carefully using "negated Int"s when looking at `fromEnumThenTo` etc.</div><div><br></div><div>I think you get the choice of keeping the same `Int` conversions, `toEnum = Down . toEnum`, or negating it, `toEnum = Down . toEnum . negate`, so e.g. 0 -> False, 1 -> True becomes 0 -> Down False, -1 -> Down True.</div><div><br></div><div>I can add potential implementations to the MR so that there is something concrete to look at (and check it all works) or do it here.<br></div><div><br></div><div>But I think it all needs a bit more discussion than I'd initially thought!</div><div><br></div><div>David.<br></div></div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Fri, Sep 18, 2020 at 3:41 PM Oleg Grenrus <<a href="mailto:oleg.grenrus@iki.fi">oleg.grenrus@iki.fi</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div>
<p>Is it (a bug)?<br>
<br>
What about [minBound .. maxBound]. If you change `Bounded`, you
need to change `Enum` too.<br>
<br>
From
<a href="https://hackage.haskell.org/package/base-4.14.0.0/docs/GHC-Enum.html#t:Enum" target="_blank">https://hackage.haskell.org/package/base-4.14.0.0/docs/GHC-Enum.html#t:Enum</a><br>
<br>
- The calls succ maxBound and pred minBound should result in a
runtime error.<br>
- enumFrom and enumFromThen should be defined with an implicit
bound</p>
<p>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`).<br>
</p>
<p>- Oleg<br>
</p>
<div>On 18.9.2020 16.54, Carter Schonwald
wrote:<br>
</div>
<blockquote type="cite">
<div dir="auto">Def a bug! Plz at myself and the core libraries
handle for code review plz. </div>
<div dir="auto"><br>
</div>
<div dir="auto">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)</div>
<div><br>
<div class="gmail_quote">
<div dir="ltr" class="gmail_attr">On Fri, Sep 18, 2020 at 7:44
AM David Beacham <<a href="mailto:mail@dbeacham.co.uk" target="_blank">mail@dbeacham.co.uk</a>> wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">
<div dir="ltr">
<div>Hi all,</div>
<div><br>
</div>
<div>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`?</div>
<div><br>
</div>
<div>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.</div>
<div><br>
</div>
<div>I've got a corresponding MR here: <a href="https://gitlab.haskell.org/ghc/ghc/-/merge_requests/4081" target="_blank">https://gitlab.haskell.org/ghc/ghc/-/merge_requests/4081</a></div>
<div><br>
</div>
<div>Thanks, David.<br>
</div>
</div>
<br>
<br>
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