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-7-bit X-Google-Thread: 103376,a00006d3c4735d70 X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2004-01-17 07:34:18 PST Path: archiver1.google.com!news2.google.com!news.maxwell.syr.edu!newsfeed.icl.net!newsfeed.fjserv.net!news-FFM2.ecrc.net!uio.no!newsfeed.kolumbus.fi!not-for-mail From: Aatu Koskensilta Newsgroups: comp.lang.ada Subject: Re: Certified C compilers for safety-critical embedded systems Date: Sat, 17 Jan 2004 17:56:47 +0200 Organization: Elisa Internet customer Message-ID: References: <0F6Nb.1623$Tt.642@reader1.news.jippii.net> NNTP-Posting-Host: 212-246-60-38.adsl.tpo.fi Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit X-Trace: phys-news1.kolumbus.fi 1074353657 10113 212.246.60.38 (17 Jan 2004 15:34:17 GMT) X-Complaints-To: abuse@kolumbus.fi NNTP-Posting-Date: Sat, 17 Jan 2004 15:34:17 +0000 (UTC) User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.2.1) Gecko/20030225 X-Accept-Language: en-us, en In-Reply-To: Xref: archiver1.google.com comp.lang.ada:4494 Date: 2004-01-17T17:56:47+02:00 List-Id: Robert I. Eachus wrote: > Aatu Koskensilta wrote: > >> (#) Surely this is not the case for arbitrary formulae? If it is, Ada >> seems rather an odd language; I've never encountered an actually used >> computer language with correctness of a program not arithmetic. > > > As far as this particular case is concerned. Yes, that is what I am > saying. Actually, back when MIL-STD 1815 was Ada and the ANSI standard > effort was in progress, I wrote an example program that was legal Ada 80 > iff Fermat's Last Theorem was true. But Fermat's Last Theorem is Pi_1. What I was saying was that I find it very unlikely that this holds for non-Pi_1 statements, even if it holds for Pi_1 ones. [Snipped an explanation on how the Halting Problem can be reduced to legality of Ada program] So your original statement [any compiler for a resonable language] either does not accept some legal programs, accepts some illegal programs, or never halts for some inputs is correct if the reasonable language we're speaking about is Ada. I think that, say, Haskell is a reasonable language, and the above does not hold for it - the type system is decidable -, but perhaps you find Haskell unreasonable. -- Aatu Koskensilta (aatu.koskensilta@xortec.fi) "Wovon man nicht sprechen kann, daruber muss man schweigen" - Ludwig Wittgenstein, Tractatus Logico-Philosophicus