Re: Flibble’s Leap: Why Behavioral Divergence Implies a Type Distinction in the Halting Problem

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

ALL C compilers are required to diagnose ALL syntax errors and ALL
constraint violations.

Yes, all conforming C compilers are required to do that.  (Well,
strictly speaking they're only required to issue at least one diagnostic
for any translation unit that violates a syntax rule or constraint.)

[...]

In my experience, Microsoft's C compiler - although not perfect - is
pretty good at following conformance rules. I'd be surprised to learn
from a competent source that it misses a syntax error.

I wouldn't, since few if any C compilers are conforming by default.

I've just tried 4 different C compilers (gcc, clang, and tcc
on Ubuntu, MS Visual Studio 2022 on Windows), and none of them
diagnosed a stray semicolon at file scope *by default*.  gcc and
clang can be persuaded to diagnose it.  tcc, as far as I can tell,
cannot; I don't believe it claims to be fully conforming in any mode.
I wasn't able to get MSVS to diagnose it, but there could easily
be an option that I'm missing.

If I wanted to prove something in mathematical logic using C code as
a vehicle, I personally would try to use fully standard-conforming C.
I *might* consider using a more lax C-like language, such as the
language accepted by some C compiler in its default mode -- but I'd
need a good reason to do that, and I'd want a rigorous definition
of anything I use that differs from standard C.

It's possible that olcott's C-like code has well defined behavior
in the implementation he's using.  If so, I'm not sure there's any
fundamental reason to use something close to C rather than using C
itself in an attempted refutation of some well known mathematical
proof.  (I wouldn't expect either C or something C-like to be a
good vehicle for such a proof.  I don't think C is defined rigorously
enough to be useful for such a task, and any C-like language is even
less so.)

olcott will likely use this to claim that I support his views.
He will be wrong.

[...]

--
Keith Thompson (The_Other_Keith) Keith.S.Thompson+u@gmail.com
void Void(void) { Void(); } /* The recursive call of the void */