Re: Overcoming the proof of undecidability of the Halting Problem by a simple example in C

On 19/05/2025 01:33, olcott wrote:

On 5/18/2025 7:27 PM, Ben Bacarisse wrote:

Richard Heathfield <rjh@cpax.org.uk> writes:

[Apologies for not snipping. This one was hard to know how best to edit down.]

>

On 18/05/2025 23:18, Ben Bacarisse wrote:

Richard Heathfield <rjh@cpax.org.uk> writes:
...

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.

Yes, but I am surprised that you are being so modern!!  You used to
favour C90 and didn't really care for anything more recent.

>
I am just as surprised that you missed the distinction I was making, which
was between these:
>
void HHH(void (*f)(void))
u32 HHH(void (*P)())
>
Empty parentheses had nothing to do with my point. On line 16 we find:
typedef uint32_t u32;
>
uint32_t != void.

>
Yes, I got the distinction you were making, but I must have got confused
about the referent of "it" in the part I quoted.  I was hoping to add
to the discussion despite ignoring your main point.  Sorry.
>

 *Copied from the original post that he responded to*
 int DD()
  {
   int Halt_Status = HHH(DD);
   if (Halt_Status)
     HERE: goto HERE;
   return Halt_Status;
  }

Not so. The post I responded to was Message-ID: <1009lm9$b15q$1@dont-email.me>
There was a lot of quoted material, none of which mentioned int DD(), although it did mention a void DDD().
The only original material was:
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
No, there are peole who do know C but don't know that HHH is not
void HHH(void (*f)(void)) {} and how therefore cannot tell that
HHH does simulate DDD.
--
Mikko
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
That's what I responded to.

HHH simulates DD that calls HHH(DD) to simulate itself
again over and over until HHH sees this repeating pattern
and aborts or both HHH and DD crash due to OOM error.

The HHH code wasn't posted in the article I responded to.

His main point was to dodge the actual meaning
of the word *simulate*

Not true. My main points were (a) a minor syntactical discrepancy between Halt7.c and Mikko's quote thereof, and (b) underlining /again/ that you have no business using the words 'Anyone that knows C' with a straight face.
--
Richard Heathfield
Email: rjh at cpax dot org dot uk
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