[Haskell-cafe] instance Enum Double considered not entirely great?

Felipe Almeida Lessa felipe.lessa at gmail.com
Wed Sep 21 06:00:22 CEST 2011

On Wed, Sep 21, 2011 at 12:47 AM, Richard O'Keefe <ok at cs.otago.ac.nz> wrote:
> In any mathematical partial order, we expect
>        x `le` x
> to be a law.  But in IEEE arithmetic, if x is a NaN, x `le` x is
> false.  I don't see how to reconcile these.
> I agree that a standard partial order class would be nice.

logfloat package's PartialOrd solution is to have

    le :: PartialOrd a => a -> a -> Maybe Bool

In IEEE arithmetic, if x is a NaN and y is anything else, x `le` y ==
y `le` x == Nothing.



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