in reply to
Re: semi-OT: Lisp code
in thread OO, Class::MethodMaker, and get_set
This is true. I was just trying to implement something as close as possible to what the original poster asked for with respect to his toy problem, which was recomputation of c whenever a or b was set. Of course it's be easy to modify things to use a cache; e.g. set c to nil (or some other convenient marker) whenever a or b is set and put a :before method on the method c that computes and sets the slot c it if it is nil.