Re: Newtype wrapper for Float/Double with sensible Eq/Ord instances

@chess, @Zemyla the ieee standard actually defines the following total order (i can send you the standard wrt the 2008 version if need be) negative nans, -inf, negative finite, 0's , positive finite, inf, positive nans (a very very different ordering than proposed here) @Zem, i would love some collab getting some RTS support into ghc for signaling nans, been a bit too busy to do all the work myself! so -1 on this proposal, and if you look back in the archives a few years ago you can see a pretty lengthy discussion around a bit more of a fleshed out proposal, though some of the end state work requires some more work on the ghc RTS the first piece needed to (subsequently implement the rest) appears in ghc 8.10, https://gitlab.haskell.org/ghc/ghc/commits/ghc-8.10.1-alpha1/compiler/cmm/Cm... https://gitlab.haskell.org/ghc/ghc/commit/42504f4a575395a35eec5c3fd7c9ef6e2b... is the overall commit it makes SSE2 the only floating point flavor on intel platform (no more x87), which simplifies a lot of 1) determinism in rounding issues that by default would plague 32bit intel platforms, and also cleaned up a pretty crufty corner of the NCG that created a lot of other spurious complexity in improving floating point stuff On Sat, Nov 30, 2019 at 1:35 PM chessai . wrote:

I would argue there is no "sensible" implementation of Eq and Ord for floating point. Better to have PartialEq [1] /PartialOrd [2].

[1]: https://doc.rust-lang.org/std/cmp/trait.PartialEq.html

[2]: https://doc.rust-lang.org/std/cmp/trait.PartialOrd.html

On Sat, Nov 30, 2019, 11:21 AM Zemyla wrote:

...

There should be a newtype wrapper that wraps a RealFloat, keeps the Enum/Num/Fractional/so on instances, but gives it sensible ones for Eq and Ord, with the following order:

NaN < -Inf < negative < -0 < +0 < positive < +Inf

It may not belong in base, but if nothing else it definitely belongs in containers, because Set and Map depend critically on sensible instances of Ord.

(Also, it should newtype derive Read and Show, so that people using them with GHCi see "fromList [(NaN, yadda), (-1.5, yadda), (2.7, blah), (+Inf, blah)]" instead of "fromList [(FloatOrd { unwrapFloat :: NaN }, yadda), ...".) _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

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