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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: Mon, 19 May 2025 01:01:34 +0100
Organization: Fix this later
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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.

> Empty ()s in a declarator were made obsolete in C17 and made equivalent
> to (void) in C23.  Prior to C23 a parameter that is pointer to a
> function taking no arguments would have to have been written as
> 
>    u32 HHH(void (*P)(void))
> 
> and after C23 the (probable) intended meaning would have to be written
> as
> 
>    u32 HHH(void (*P)(...))

but not void HHH(void (*f)(void)), eh?

> (Caveat: I'm not properly up to date anymore and, this not being
> comp.lang.c, I may not be corrected by People Who Really Know.)

I have no doubt you're right about (), but that wasn't the point 
I was making.

-- 
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