Re: question about linker

Bart <bc@freeuk.com> writes:

On 07/12/2024 14:36, Janis Papanagnou wrote:

On 07.12.2024 14:04, Bart wrote:
Just fine, I'd say.
 

But it relies on some subtlety.

You seem to see ghosts. There's no subtlety; all is clearly defined,
and it's a sensible feature, and consistently implemented.
 

'while (cond)' both starts a statement, and can
end a statement:
>
    do while(cond) do ; while (cond);

What is this (IMO syntactical wrong "C" code) supposed to do or to
explain?

>
See my follow-up.
>

Your (wrong) second 'do' was indeed confusing! - Why did you provide
a wrong sample to confirm your wrong ideas? - Or is it just your well
known habit to try to confuse other folks as well my making up stupid
things?

>
You're being aggressive. It was a mistake, that's all. My original
example was meant to show how it gets confusing, but when I
transcribed it into an actual program, it seemed to work because I'd
left out that 'do'.

OK, it was a mistake.  Someone pointed it out.  And you took offense at
that for some reason.

It says something however when I actually believed that that code was
valid, because the compiler appeared to say so.

It doesn't say anything interesting.

Most here (and me too) already acknowledged that "C" is not obvious
to you.

>
Why is it not possible for to acknowledge that some language design
patterns may not be as obvious as others?

It is.  Don't lie.

According to you, even if some construct can be determined to be
unambiguous in some convoluted grammar, then it must also be 100%
obvious to any human reader?

Nobody said that.  Don't lie.

Is it just to avoid admitting that I might have a point?

What point is that?  That C can be confusing?  We all know that.

You don't think there is an element of ambiguity here?

There isn't any.

>
So you're a parser and you see this:
>
    do ... while
>
How do you know whether that 'while' starts a new nested loop or
terminates this one?

If I'm a parser, then I was written to follow the grammar, which
happens to be unambiguous.

If I'm a human reader, 99+% of the time the code will have been
formatted to avoid any apparent ambiguity.  In a do-while loop, the last
line typically of the form "} while (cond);", and the closing "}"
matches the opening "do {".  If I somehow miss the semicolon, the fact
that the following line is not a "{" and is at the same indentation is a
strong clue.

Some coding styles might use:

    do
    {
        statements;
    }
    while (cond);

but even that isn't difficult to understand.

Some years ago, I wrote some C code that deliberately made the
"while (cond)" of a do/while loop appear to be part of a while loop.
It was for a submission to the IOCCC <https://www.ioccc.org/>.

If you go out of your way to make C code appear ambiguous, it
will appear ambiguous (to a human reader if not to a compiler).
I rarely do that.  You do it far too often.

What does it depend on; what property of blocks in the language is
needed to make it work? What property of statement separators or
terminators is needed.

[snip]

So it can't work in a syntax which allows N statements in a block:
>
  do s1; s2; s3; while ...

C doesn't allow that, so it doesn't matter.

Since it can't tell whether that while is the terminator, or is
another nested loop.

You take the fact that a do/while or while loop controls a single
statement, and distort it with irrelevancies to make it seem like a
problem.

[...]

You might also have pointed out that C could have deprecated null
statements consisting of a single ";", and required the more visible
"{}", as some compilers can be requested to do. Since such a ";" can
instroduce very subtle errors that are hard to spot.

I don't know of any such compiler options.  But apparently you don't use
it yourself, since you've recently complained about the need to emit
"L:;" in generated C code.  If you used that option, you'd have to emit
"L:{}".  You invent a problem that apparently doesn't even affect you,
and pretend that it must affect others.

That the option exists suggests that some people do have trouble with
it. But your attitude appears to be the arrogant one that because it
is technically unambiguous, then ANYONE should be able to spot such
errors.

No, Janis merely stated that the syntax is unambiguous.  Which, as you
know, it is.

And if they can't then they should spend more time studying manuals,
choose a different language, or give up coding altogether.
>
In your book, it's fine to write expressions like this:
>
  a + b & c * d == f < g | h ? i ^ j : k && l
>
without parentheses, because the C grammar is 100% unambiguous in what
it means.

Nobody said that.  Don't lie.

Yes, C can be confusing.  When have you ever written anything with the
intent of clearing up the confusion?

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