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: 103376,54e6f3bfd18d2769 X-Google-Attributes: gid103376,public X-Google-ArrivalTime: 2000-10-30 07:28:26 PST Newsgroups: comp.lang.ada Path: supernews.google.com!sn-xit-02!sn-xit-03!supernews.com!logbridge.uoregon.edu!news.umass.edu!world!bobduff From: Robert A Duff Subject: Re: Pointer function parameter Sender: bobduff@world.std.com (Robert A Duff) Message-ID: Date: Mon, 30 Oct 2000 15:24:26 GMT References: <8ss92s$6fs$1@nnrp1.deja.com> <39F473DD.1CBAE902@cepsz.unizar.es> <39F5A744.CB20A0FD@cepsz.unizar.es> Organization: The World Public Access UNIX, Brookline, MA X-Newsreader: Gnus v5.3/Emacs 19.34 Xref: supernews.google.com comp.lang.ada:1630 Date: 2000-10-30T15:24:26+00:00 List-Id: Alejandro Villanueva <190921@cepsz.unizar.es> writes: > Robert A Duff wrote: > > > Alejandro Villanueva <190921@cepsz.unizar.es> writes: > > > > > You are right! Turing machines can do ANYTHING, ... > > > > No, they can't! > > wops! please, explain me that... For your amusement, here's a list of some things a Turing machine (TM) can't do: A TM cannot calculate, in finite time, the last prime number, nor produce the full decimal expansion of pi. A TM cannot handle interrupts. A TM cannot make a soft-boiled egg. The machine has no peripheral devices such as a stove, but more importantly, it has no concept of real time (which is key for soft-boiled eggs). In general, a TM can't run real-time programs. A TM cannot produce high quality original works of fiction. A TM cannot convince me I should vote for Pat Buchanan. A TM cannot write a large, useful, bug-free computer program. And never will. A TM cannot drive a GUI interface -- the machine has no bit-mapped display, but more importantly, it has no concept of doing I/O as it goes along. That is, a TM's input is placed on the tape before the machine starts, and you don't look at the output until it halts. GUI's don't fit into that I/O model. Some computing devices, such as normal computers, and human brains, *can* do some of these things! Oh, one last thing: a TM cannot "exist". (Does that fall under your definition of "do ANYTHING"?) A TM has an infinitely long tape, whereas we can only build machines with finite memories. (The hardware folks are getting closer and closer to infinite-sized memories all the time, but they still have a long way to go. Besides, the software folks can use it up faster than it grows.) ;-) - Bob