Unclear explanation of why Float and Double do not have additive identities

Summary

Location of documentation issue: the Haddock comments for the Float and Double instances of Num in GHC.Float (search for the word "additive").

This example gives the impression that -0 :: Float could be the additive identity. After all,

x + (-0 :: Float) == x || isNaN x

holds for all x :: Float. Besides, GHCi reports that (-0 :: Float) == 0 holds, as required by the IEEE-754 standard, so they're sometimes considered to be equivalent values.

Wouldn't it be clearer to use the existence of NaN values to prove that the additive identity doesn't exist? I.e. neither e=0 nor e=(-0 :: Float) satisfies

let x = (0/0 :: Float) in x + e == x

Proposed improvements or changes

It would be clearer to say:

-- Also note that due to the presence of @NaN@, `Float`'s 'Num' instance doesn't
-- have an additive identity
--
-- >>> let nan = (0/0 :: Float) in nan + 0 == nan
-- False

and to make a similar change to the comment for the Double instance.

I'd be happy to create a pull request if the relevant developers agree to this change.