Re: D correctly simulated by H cannot possibly reach its own line 06 and halt

On 2024-06-01 14:44:50 +0000, olcott said:

On 6/1/2024 2:56 AM, Mikko wrote:

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.
 

 When a pure function returns this is the equivalent of the theory
of computation halting.

In ceratin sense, yes. But the term "pure function" is mainly used
in a different context where the word "halting" has a more specific
meaning.
--
Mikko