Re: Proposal: add Bounded instances for Maybe and Either

minBound = Left minBound <= Left a < Right b <= Right maxBound = maxBound fits with the behavior of the existing Ord instance. On the other hand, Left (), being strictly less than minBound would rather drastically undermine the expected interaction of Ord and Bounded. -Edward On Tue, May 8, 2018 at 1:06 AM, Ivan Lazar Miljenovic < ivan.miljenovic@gmail.com> wrote:

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We can write

instance Bounded a => Bounded (Maybe a) where minBound = Nothing maxBound = Just maxBound

instance (Bounded a, Bounded b) => Bounded (Either a b) where minBound = Left minBound maxBound = Right maxBound

While Bounded intentionally does not have an Ord superclass, I think it's worth mentioning that these are the instances that arise naturally from

On 8 May 2018 at 13:19, David Feuer wrote: the

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Ord instances for the types in question.

Except these may be surprising to people; e.g. someone may expect that `minBound = Right minBound` as well. Though as Maybe and Either don't have Enum instances this may be less of an issue.

-- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com http://IvanMiljenovic.wordpress.com _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries