From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <3C7D4A93.D641124E@acm.org> From: Graham Gallagher MIME-Version: 1.0 To: 9fans@cse.psu.edu Subject: Re: [9fans] GUI toolkit for Plan 9 References: <87heo4ylg9.fsf@becket.becket.net> <20020227122932.M26250@cackle.proxima.alt.za> <3C7CCF42.C052DD9F@acm.org> <20020227145912.Q26250@cackle.proxima.alt.za> Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Date: Thu, 28 Feb 2002 08:07:31 +1100 Topicbox-Message-UUID: 59be07f4-eaca-11e9-9e20-41e7f4b1d025 Lucio De Re wrote: > > On Wed, Feb 27, 2002 at 11:21:22PM +1100, Graham Gallagher wrote: > > > > "Doug McIlroy (Bell Laboratories) disagrees with this argument, claiming > > that correct programs *are* made from incorrect parts. Telephone control > > programs, for example, are more than half audit code, whose business is > > to recover from unintended states, and the audit code has been known to > > mask software as well as hardware errors." > > Now I'm obtuse. From the above, I can't decide whether that means > that enough code will catch all possible errors (quis custodet > custodes?) or that one can insanely keep chasing one's own tail. > > I think the jury will stay out on that one :-) > > I wouldn't mind some clarification as to "this argument" mentioned in > the quote. I don't have a copy of Gries's book handy :-) The McIlroy quote was a counterexample to the argument: "Suppose a program consists of n small components - i.e. procedures, modules - each with probability p of being correct. Then the probability P that the whole program is correct certainly satisfies P < p^n".