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),
...".)
