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Path: news.eternal-september.org!eternal-september.org!.POSTED!not-for-mail From: Richard Heathfield <rjh@cpax.org.uk> Newsgroups: comp.theory Subject: Re: Overcoming the proof of undecidability of the Halting Problem by a simple example in C Date: Sun, 18 May 2025 12:05:58 +0100 Organization: Fix this later Lines: 38 Message-ID: <100ceum$uvq0$1@dont-email.me> References: <1005jsk$3akrk$1@dont-email.me> <bc6f0f045212bdfb7f7d883426873a09e37789ea@i2pn2.org> <1005u6v$3cpt2$1@dont-email.me> <1005v0p$3b07v$1@dont-email.me> <10063u0$3dmiv$1@dont-email.me> <1006on8$3l9t7$1@dont-email.me> <1007kgq$3qb7l$9@dont-email.me> <1009lm9$b15q$1@dont-email.me> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Injection-Date: Sun, 18 May 2025 13:06:02 +0200 (CEST) Injection-Info: dont-email.me; posting-host="99c2e759ba7e03b4721635ed22ed06d2"; logging-data="1015616"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18O128FLmoC8AeBpj3KspOeOJlCA1jaLwVQiGxnJohW1w==" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:Ao8c9VFrBwyPctkv+9v/nehxaWQ= Content-Language: en-GB In-Reply-To: <1009lm9$b15q$1@dont-email.me> On 17/05/2025 10:42, Mikko wrote: > On 2025-05-16 15:10:18 +0000, olcott said: > <snip> >> void DDD() >> { >> HHH(DDD); >> return; >> } >> >> Anyone that knows C can tell that when HHH does simulate >> DDD correctly that it keeps getting deeper in recursive >> simulation until aborted or OOM error. > > No, there are peole who do know C but don't know that HHH is not > void HHH(void (*f)(void)) {} If they know C they should know that it's u32 HHH(void (*P)()), according to Halt7.c. It takes a pointer to a function that accepts no arguments and returns no value. Anyone who knows C will know that HHH can call the function pointed to, pass it on to another function as a parameter, or store the value. If it does anything else with that value (which of course it *does*), C washes its hands of the consequences. Mr Olcott is mistaken to think that HHH()'s behaviour can be determined by the rules of C. -- Richard Heathfield Email: rjh at cpax dot org dot uk "Usenet is a strange place" - dmr 29 July 1999 Sig line 4 vacant - apply within