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From: Mikko <mikko.levanto@iki.fi>
Newsgroups: comp.theory
Subject: Re: Every D(D) simulated by H presents non-halting behavior to H ###
Date: Thu, 16 May 2024 13:48:49 +0300
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On 2024-05-15 15:24:57 +0000, olcott said:

> On 5/15/2024 3:18 AM, Mikko wrote:
>> On 2024-05-14 14:35:42 +0000, olcott said:
>> 
>>> On 5/14/2024 4:52 AM, Mikko wrote:
>>>> On 2024-05-13 14:43:09 +0000, olcott said:
>>>> 
>>>>> On 5/13/2024 4:14 AM, Mikko wrote:
>>>>>> On 2024-05-13 04:54:30 +0000, immibis said:
>>>>>> 
>>>>>>> On 10/05/24 19:55, Alan Mackenzie wrote:
>>>>>>>> [ Followup-To: set ]
>>>>>>>> 
>>>>>>>> In comp.theory olcott <polcott333@gmail.com> wrote:
>>>>>>>> 
>>>>>>>> [ .... ]
>>>>>>>> 
>>>>>>>> I've tried out your much spammed code on GCC (see below).  It is clear
>>>>>>>> you have never built or run this code, which ironically can't reach Line
>>>>>>>> 06.  It can't even reach line 00.
>>>>>>>> 
>>>>>>>>> Richard tried to get away with D never simulated by H as an example
>>>>>>>>> of D simulated by H:
>>>>>>>> 
>>>>>>>>> Message-ID: <v0ummt$2qov3$2@i2pn2.org>
>>>>>>>>> On 5/1/2024 7:28 PM, Richard Damon wrote:
>>>>>>>> 
>>>>>>>>> *That people say they know I am wrong yet will not show the detailed*
>>>>>>>>> *steps of how I am wrong indicates that they are probably liars*
>>>>>>>> 
>>>>>>>> You have said, or at least implied that your code fragment is runnable.
>>>>>>>> I think you are the liar, here.
>>>>>>>> 
>>>>>>>>> 00 int H(ptr x, ptr x)  // ptr is pointer to int function
>>>>>>>>> 01 int D(ptr x)
>>>>>>>>> 02 {
>>>>>>>>> 03   int Halt_Status = H(x, x);
>>>>>>>>> 04   if (Halt_Status)
>>>>>>>>> 05     HERE: goto HERE;
>>>>>>>>> 06   return Halt_Status;
>>>>>>>>> 07 }
>>>>>>>>> 08
>>>>>>>>> 09 int main()
>>>>>>>>> 10 {
>>>>>>>>> 11   H(D,D);
>>>>>>>>> 12 }
>>>>>>>> 
>>>>>>>> 
>>>>>>>> .  These are the diagnostics generated by GCC:
>>>>>>>> 
>>>>>>> And the halting problem is about Turing machines, anyway.
>>>>>> 
>>>>>> Not necessarily. The same question can be asked about different machines.
>>>>>> The restriction to Turing machines is just one way to ensure that the
>>>>>> problem is well defined.
>>>>>> 
>>>>> 
>>>>> Well put. All computable functions even if written in C.
>>>> 
>>>> You still must ensure that the problem is well defined. With C there is
>>>> the problem that conforming C programs often fail to be strictly conforming.
>>>> If a program is not strictly conforming it may be interpreted as halting
>>>> by some implementation and non-halting or incorrect by another.
>>>> 
>>> 
>>> 00 int H(ptr x, ptr x)  // ptr is pointer to int function
>>> 01 int D(ptr x)
>>> 02 {
>>> 03   int Halt_Status = H(x, x);
>>> 04   if (Halt_Status)
>>> 05     HERE: goto HERE;
>>> 06   return Halt_Status;
>>> 07 }
>>> 08
>>> 09 int main()
>>> 10 {
>>> 11   H(D,D);
>>> 12 }
>>> 
>>> One can correctly determine that every D simulated by H
>>> never reaches past its own line 03.
>> 
>> That is not strictly conforming and hardly conforming at all.
>> 
> 
> What trivial syntactic error that has no effect
> what-so-ever on the semantics do you believe remains?

A trivial sysntactic error means that the program is not strictly
conforming. It may be conforming if some liberal compiler accepts
it.

> A missing semi-colon?

Normal semantics is that the program is not executed.

> typedef int (*ptr)();  // ptr is pointer to int function
> 00 int H(ptr x, ptr x);
> 01 int D(ptr x)
> 02 {
> 03   int Halt_Status = H(x, x);
> 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 }

Can you find any compiler that is liberal enough to accept that?

-- 
Mikko