On 12/3/07, Yitzchak Gale
In this case, the Ord instance is not really natural; it is defined for technical reasons for use by the library itself (and its friends). The library has no need for a Bounded instance, so why should we prevent people from defining one for some other purpose?
Note that in one sense, people are already prevented from defining a different Bounded instance. Any Bounded instance other than the one suggested in this proposal would fail to obey the axioms of the Bounded class. In other words, there is a unique largest element, and a unique smallest element, an no one can legitimately define a different Bounded instance. Given that the Bounded instance is uniquely defined, I think it is more convenient to have it defined by the library than to have to manually define it in every program that uses it.