On Sun, Jun 29, 2014 at 4:28 AM, <ok@cs.otago.ac.nz> wrote:

On the subject of Double and laws, I imagine it would have been
possible to do the kind of thing the SML Basis Library does for
equality. SML spells equality '=' and it's not defined on the
floating point types, which have a *different* operator, '=='.

If you do that, where do you stop? Not all Int's have additive inverses, and most floats have multiple things they can be added to that don't change their value. Can we call both of those +? Or do we need a name for them or two?

Actually, I don't know if SML got it right or not, because I don't know what the "==" operator does. But you should *never* compare floats for equality. While there are exceptions, they are so rare that you're likely never to run into one, so just be safe, and don't do it.

So if SML's "==" operator is an equality comparison, they at best got it half right. If it's some kind of programmer-controlled "fuzzy equality", well, maybe. But I think just leaving it out would be a better solution.

In the same way, the Prelude could have been structured so that
integers and ratios belonged to Ord but floats did not. Floats
could have had operators like #< #= instead. It would have been
surprising, but so is x == x being False surprising.

Is x == x being false really any more surprising than x + 1 == x being true?