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*To*: dlw at SCRC-TENEX at MIT-MC*Subject*: Re: x^0.0*From*: HEDRICK at RUTGERS (Mgr DEC-20s/Dir LCSR Comp Facility)*Date*: Wed, 01 Dec 1982 22:10:00 -0000*Cc*: Kim.fateman at UCB-C70, common-lisp at SU-AI*In-reply-to*: Your message of 1-Dec-82 1706-EST

I would like for any computation that doesn't have a well-defined value to be either an error or result in some item which can never turn into a normal number, even after being multiplied by 0.0. The problem with things like +UNDEFINED is that when you multiply them by 0.0, you get 0.0. But depending upon the exact expression involved and how you take the limit, that is not necessarily a good result. The problem with +UNDEFINED or +INF is that you have only choices, neither of them very attractive: - make them contagious. Any computation involving one of them produces a result that is either UNDEFINED or INF. The problem there is that you can do an hour-long computation that returns UNDEFINED, and have no idea where the error occured. - make 0 * UNDEFINED = 0. But that can result in meaningless answers. It seems that you you supply, at least as an option, the ability to generate an error whenever something questionable is happening. -------