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,FREEMAIL_FROM autolearn=unavailable autolearn_force=no version=3.4.4 X-Received: by 10.200.49.153 with SMTP id h25mr15664552qte.13.1467002937779; Sun, 26 Jun 2016 21:48:57 -0700 (PDT) X-Received: by 10.157.43.150 with SMTP id u22mr583606ota.17.1467002937721; Sun, 26 Jun 2016 21:48:57 -0700 (PDT) Path: eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!mx02.eternal-september.org!feeder.eternal-september.org!goblin3!goblin1!goblin.stu.neva.ru!w59no1300781qtd.1!news-out.google.com!o189ni3085ith.0!nntp.google.com!r1no3537522ige.0!postnews.google.com!glegroupsg2000goo.googlegroups.com!not-for-mail Newsgroups: comp.lang.ada Date: Sun, 26 Jun 2016 21:48:57 -0700 (PDT) In-Reply-To: <57707888$0$5274$426a34cc@news.free.fr> Complaints-To: groups-abuse@google.com Injection-Info: glegroupsg2000goo.googlegroups.com; posting-host=2601:191:8202:8510:5985:2c17:9409:aa9c; posting-account=fdRd8woAAADTIlxCu9FgvDrUK4wPzvy3 NNTP-Posting-Host: 2601:191:8202:8510:5985:2c17:9409:aa9c References: <57346ac8$0$4570$426a74cc@news.free.fr> <57707888$0$5274$426a34cc@news.free.fr> User-Agent: G2/1.0 MIME-Version: 1.0 Message-ID: <43a09f40-fdea-461e-9b0a-4419b86c1a56@googlegroups.com> Subject: Re: Ada.Strings.Fixed.Count raises Storage_Error From: rieachus@comcast.net Injection-Date: Mon, 27 Jun 2016 04:48:57 +0000 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Xref: news.eternal-september.org comp.lang.ada:30953 Date: 2016-06-26T21:48:57-07:00 List-Id: On Sunday, June 26, 2016 at 8:51:21 PM UTC-4, Xavier Petit wrote: =20 > Every parameters of a subprogram should be anticipated and produce a=20 > coherent behavior. It=E2=80=99s hard but Ada is especially here to make i= t easier. G=C3=B6del, Escher, Bach: An Eternal Golden Braid, is a 1979 book by Dougla= s Hofstadter that is now in its 20th edition. It tries, among other things to explain the reality revealed by G=C3=B6del'= s proofs. One of those consequences is that you can't build a perfect comp= iler. In fact, the gnat in Ada Core Technologies logo is a cute reminder t= hat every compiler must have at least one bug. Not, these things are so co= mplex they can never be perfect, but even some very simple software tools a= re subject to G=C3=B6del's findings--no system above a rudimentary complexi= ty (embedding of Peano arithmetic) can be bug-free. Worse, the Halting Problem is a very simple proof that you cannot write a p= rogram that will perfectly determine whether a given software program will = halt. (Or not halt, if you work on embedded systems like I did.) So trying for perfection in compilers, programming languages, and even many= software programs is a mug's game. You can't do it, you don't know where = other corner cases are, and you can't even document all of the bugs. Yes, = it is possible to "prove" software correctness for some programs. But for = those same programs, you have just moved the target, from perfect software = to perfect requirements. The Airbus 320 had a major software bug in spite of the correctness proof t= ools used. If a plane cross the last waypoint before the destination, the = flight guidance system would put the airplane in the correct glidepath for = the chosen runway as quickly as possible, even if that location was under a= few thousand feet of granite. Strasbourg suddenly dove straight down. Oo= ps! Perfect software implementation of a bad requirement. (https://www.flig= htglobal.com/news/articles/air-france-ceo-jean-cyril-spinetta-defends-rejec= tion-of-gpws-equipment-on-air-inter-a320-fleet-despite-fatal-1992-st-odile-= mountainside-crash-210280/ The obfuscation thrown about by Airbus and the F= rench government still continues. But at least the bug in "flight path ang= le mode" in the flight controller got fixed. This list will show you why I= still won't fly on an Airbus 310,20, or 21: https://en.wikipedia.org/wiki/= Accidents_and_incidents_involving_the_Airbus_A320_family ) =20