> It would be nice to be able to have the features of all 3 in a single
> type.... in other words a memo-function whose stored keys you could
> retrieve.

Doesn't this make the result dependent on order of execution?

Given the expression

f(1), f(2), keys(f#1), f(3), f(4)

are you expecting that keys(f#1) will return (1,2)? If so, that's certainly
non-deterministic.

Michael Kay
Saxonica