Re: [Scheme-reports] R7RS-large comparators

This is an excellent point. I would just like to add that it also makes it trivial to extend the comparator interface to partial orders - they could return 'not-comparable if their arguments couldn't be ordered.

Best,
Noah Lavine

On Mon, Jul 15, 2013 at 7:28 PM, Kevin Wortman <kwortman@x> wrote:

On 07/12/2013 08:51 AM, John Cowan wrote:
> Ray Dillinger scripsit:
>
>> On floating point numbers it would make sense (to me anyway) to return -0.0
>> in the case of a comparison of +0 and -0, and return NaN in the case of any
>> comparison involving NaNs.
>
> In this context, that would mean returning one of five values:
>
> return 1 when A > B
>
> return 0 when A = B, unless one is 0.0 and the other is -0.0
>
> return -0.0 when one is 0.0 and the other is -0.0
>
> return -1 when A < B
>
> return +nan.0 when A is NaN or B is NaN
>
> This seems extremely irregular.
>

I think that a comparator returns one of three conceptual results:
less-than, equal, or greater-than. There is a long history of using the
integer values -1, 0, and +1 to represent those concepts. However these
concepts are not really integers, and using integers to represent them
may be a red herring. I think Haskell gets this right by yielding one of
the algebraic constructors LT, EQ, or GT (
http://www.haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#t:Ordering
).

Perhaps Scheme comparators should return one of the symbols 'less 'equal
or 'greater ? Or perhaps we should standardize enumerated types first
and then have comparators return an enum object.

Kevin Wortman

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