On 4/28/12 12:10 PM, Sjoerd Visscher wrote:
But I don't think an unfoldable class for * types is that interesting. Any type that would be an instance could also be in instance of Bounded and Enum:
In a technical sense, yes, but not necessarily in a semantic sense. Usually Bounded and Enum are expected to respect the natural ordering on the type; and, given Eq, they induce an ordering on the type (albeit an inefficient one). But there are plenty of cases where you don't have a natural ordering, or where it would be more efficient to enumerate values in an unnatural order if the goal is just to get them all. Unfortunately, we don't have a good way of distinguishing between natural vs ad-hoc enumerations/orderings, so this sort of thing gets handled poorly on case-by-case bases. Though I agree that Biunfoldable is a lot more interesting than Unfoldable0. -- Live well, ~wren