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From: Mikko <mikko.levanto@iki.fi>
Newsgroups: comp.theory
Subject: Re: D correctly simulated by H cannot possibly reach its own line 06 and halt
Date: Sat, 1 Jun 2024 10:56:24 +0300
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On 2024-05-31 14:25:40 +0000, olcott said:
> On 5/31/2024 2:50 AM, Fred. Zwarts wrote:
>> Op 31.mei.2024 om 00:01 schreef olcott:
>>> On 5/30/2024 4:54 PM, joes wrote:
>>>> Am Thu, 30 May 2024 09:55:24 -0500 schrieb olcott:
>>>>
>>>>> typedef int (*ptr)(); // ptr is pointer to int function in C
>>>>> 00 int H(ptr p, ptr i);
>>>>> 01 int D(ptr p)
>>>>> 02 {
>>>>> 03 int Halt_Status = H(p, p);
>>>>> 04 if (Halt_Status)
>>>>> 05 HERE: goto HERE;
>>>>> 06 return Halt_Status;
>>>>> 07 }
>>>>> 08
>>>>> 09 int main()
>>>>> 10 {
>>>>> 11 H(D,D);
>>>>> 12 return 0;
>>>>> 13 }
>>>>>
>>>>> The left hand-side are line numbers of correct C code.
>>>>> This code does compile and does conform to c17.
>>>>>
>>>>> Everyone with sufficient knowledge of C can easily determine that D
>>>>> correctly emulated by any *pure function* H (using an x86 emulator)
>>>>> cannot possibly reach its own simulated final state at line 06 and halt.
>>>> Yeah, of course not, if H doesn’t halt.
>>>>
>>>
>>> To actually understand my words (as in an actual honest dialogue)
>>> you must pay careful attention to every single word. Maybe you
>>> had no idea that *pure functions* must always halt.
>>>
>>> Or maybe you did not know that every computation that never reaches
>>> its own final state *DOES NOT HALT* even if it stops running because
>>> it is no longer simulated.
>>
>> Since the claim is that H is also a computation, it holds for H, as
>> well. That means that H *DOES NOT HALT* even if it stops running
>> because it is no longer simulated.
>>
>
> *pure function H definitely halts you are confused*
A pure function does not halt (in C that means that a pure function
does not call exit). A pure function returns.
--
Mikko