On Fri, Apr 24, 2015 at 9:06 AM, Ivan Lazar Miljenovic
What is the validity of defining an Ord instance for types for which mathematically the `compare` function is partially ordered?
Defining Ord instances for types which are not totally ordered is *wrong*. For example, due to the existence of NaN values, Double/Float are not totally ordered and therefore their Ord instances are buggy. In my logfloat package I have to explicitly add checks to work around the issues introduced by the buggy Ord Double instance. This is why I introduced the PartialOrd class, and I'm not the first one to create such a class. We really ought to have an official PartialOrd class as part of base/Prelude. The only question is whether to use Maybe Ordering or a specially defined PartialOrdering type (the latter optimizing for space and pointer indirection; the former optimizing for reducing code duplication for manipulating the Ordering/PartialOrdering types). -- Live well, ~wren