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
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