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=-1.9 required=5.0 tests=BAYES_00 autolearn=ham autolearn_force=no version=3.4.4 X-Google-Language: ENGLISH,ASCII X-Google-Thread: 103376,a00006d3c4735d70 X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2004-01-21 00:05:32 PST Path: archiver1.google.com!news2.google.com!news.maxwell.syr.edu!news.tele.dk!news.tele.dk!small.news.tele.dk!newsfeed.bahnhof.se!feeder1.news.jippii.net!reader1.news.jippii.net!53ab2750!not-for-mail From: Aatu Koskensilta User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:1.5) Gecko/20030925 X-Accept-Language: en-us, en MIME-Version: 1.0 Newsgroups: comp.lang.ada Subject: Re: Certified C compilers for safety-critical embedded systems References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 8bit Message-ID: Date: Wed, 21 Jan 2004 10:07:33 +0200 NNTP-Posting-Host: 195.74.11.141 X-Complaints-To: newsmaster@saunalahti.com X-Trace: reader1.news.jippii.net 1074672283 195.74.11.141 (Wed, 21 Jan 2004 10:04:43 EET) NNTP-Posting-Date: Wed, 21 Jan 2004 10:04:43 EET Organization: Saunalahti Customer Xref: archiver1.google.com comp.lang.ada:4592 Date: 2004-01-21T10:07:33+02:00 List-Id: Robert I. Eachus wrote: > Aatu Koskensilta wrote: > >> The Halting Problems speaks about recursive functions. In order to >> make applications of it to a real world situation, you have to be able >> to see some things in the situation as being recursive functions. >> Otherwise Halting Problem tells you nothing about the situation. > > > The Halting problem and G�del's proof are two sides of the same coin, at > least in computer science. The Halting problem is a constructive proof > of G�del's proof. How is that? In what sense was G�del's original proof non-constructive? > If a language allows partial recursive functions, then it is Turing > complete, and there is no general solution of the halting problem. You > can write a program that solves the halting problem correctly for some > inputs. But there are either inputs for which the program produces > incorrect outputs, or there are inputs for which it never halts. (And > it is not difficult to prove that for some inputs, you won't be able to > determine if the halting problem program will eventually halt.) Why is this relevant to the question of whether a compiler can correctly recognise all legal programs and reject all illegal ones? Most languages do not define "legal" by means of undecidable run-time behaviour. Perhaps Ada is different here. You mentioned earlier that producing a C++ program which would defeat a given compiler was "trivial". Could you provide some details? -- Aatu Koskensilta (aatu.koskensilta@xortec.fi) "Wovon man nicht sprechen kann, daruber muss man schweigen" - Ludwig Wittgenstein, Tractatus Logico-Philosophicus