Proposal (long term): Remove (/=) from Eq; change the semantics of (==) for floating point

[John Lato]

This strikes me as a halfway measure between those who want arithmatic
operations on Float/Double to be fast (i.e. IEEE754 semantics/machine ops)
and those who want more exacting laws associated with arithmatic classes.
As such, I think it's a bad idea.  I think it's better that all operations
follow the same philosophy.

On Thu, Sep 25, 2014 at 11:25 AM, David Feuer <david.feuer at gmail.com> wrote:

> As Edward Kmett explained to me, (/=) is currently needed in Eq to support
> IEEE floating point semantics for (==) and (/=). As I see it, those
> semantics are badly broken from the perspective of what Eq is supposed to
> mean, and really should be supported using special functions (eqIEEE and
> neqIEEE or whatever), whereas the most appropriate Eq instance for floating
> point would be something more like
>
> instance Eq Double where
>   x == y   =  decodeFloat x == decodeFloat y
>
> If this is (eventually) done, that would allow us to remove (/=) from Eq,
> reducing its dictionary to a single member, (==), improving efficiency when
> the type is not statically known.
>
> David
>
> _______________________________________________
> Libraries mailing list
> Libraries at haskell.org
> http://www.haskell.org/mailman/listinfo/libraries
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://www.haskell.org/pipermail/libraries/attachments/20140925/f00bb3d1/attachment.html>