Proposal: add an order-reversing newtype to Data.Ord

[ARJANEN Loïc Jean David]

I have created a ticket for the proposal on GHC's Trac (see here:
http://hackage.haskell.org/trac/ghc/ticket/7077). I didn't asked for the
maintainer's advice before opening a ticket given that the maintener is
libraries at haskell.org and there wasn't any opposition.
Based on this list advice, I finally decided to just re-export
GHC.Exts's newtype for the proposal's purposes, so that this proposal
doesn't get bikeshedded to death on the newtype's name.

Regards,
ARJANEN Loïc

On 2012-06-28 12:01, ARJANEN Loïc Jean David wrote :
> Hello all,
>
> I recently noticed that despite conversations about that in this
> mailing-list, there isn't an order-reversing newtype in Data.Ord.
> That newtype would be quite useful, e.g. for reverse-sorting a list or
> a set, so I propose we add a newtype defined thusly:
>
>    newtype Reverse a = Reverse { fromReverse :: a } deriving (Eq)
>
>    instance Ord a => Ord (Reverse a) where
>       compare (Reverse x) (Reverse y) = compare y x
>
> I took the implementation from the Down newtype in GHC.Exts, so we
> could perhaps just re-export it.
> This will cause breakage to code already defining a type named
> Reverse, so I don't know if the damage will be important. Of course,
> the name and definition are open to discussion.
>
> Deadline: 12 July 2012.
>
> P.S. : A conversation about that took place here:
> http://haskell.1045720.n5.nabble.com/A-Down-newtype-in-Data-Ord-td5005373.html
>
-- 
ARJANEN Loïc Jean David
http://blog.luigiscorner.com
--- 
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