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 <[email protected]> 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 > > > > _______________________________________________ > Scheme-reports mailing list > [email protected] > http://lists.scheme-reports.org/cgi-bin/mailman/listinfo/scheme-reports > >
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