This sounds like a good idea to me. The distinction of a parameter error, a not-implemented error and a known bug in an implementation (that one I hadn't added yet, only proposed) is one that the user is probably not interested in at all. So this makes for a good replacement for all three.

Sent from my iPhone

On 22 Aug 2016, at 18:50, Robert Goldman rpgoldman@sift.net wrote:

What about an UNSUPPORTED-FUNCTIONALITY ERROR subclass?

I was thinking of putting it in UIOP, and exported, for the use of cases where a particular implementation doesn't support an operation.

This might make it much easier to handle implementations that don't support all operations, PARTICULARLY in test cases.

Best, r