From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=0.2 required=5.0 tests=BAYES_00,INVALID_MSGID, REPLYTO_WITHOUT_TO_CC autolearn=no autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: 103376,86fd56abf3579c34 X-Google-Attributes: gid103376,public From: brh@cray.com (Brian Hanson) Subject: Re: What good is halting prob? Date: 1995/04/21 Message-ID: <1995Apr21.090941.7763@driftwood.cray.com>#1/1 X-Deja-AN: 101370071 references: organization: Cray Research, Inc., Eagan, MN reply-to: brh@cray.com newsgroups: comp.lang.ada originator: brh@fir306 Date: 1995-04-21T00:00:00+00:00 List-Id: In article 3v1@netcom.com, cpp@netcom.com (Robin Rowe) writes: > In practice it is not feasible to statically eliminate the cannot_tell > cases because a real computer doesn't have an infinite tape (or time). It > can be painted into a corner. What I think is achievable is to design a > program that knows it doesn't know and fails gracefully. BZZZZT! Wrong. You can design a program to fail gracefully but you cannot in general design a program to know that it doesn't know. You can have a program attempt a calculation and give it a time limit to accomplish it but your program cannot know whether the calculation would have finished one microsecond after your time limit or taken forever. -- -- Brian Hanson -- brh@cray.com