Re: stopping a loop iteration without exiting it

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On 11/01/2018 21:54, G. B. wrote:
> Dmitry A. Kazakov <mailbox@dmitry-kazakov.de> wrote:
> 
>>>> I have no idea what this is supposed to mean.
>>>
>>>
>>> L:
>>> [for|while...] loop
>>> ...
>>> goto L;
>>> ...
>>> end loop L;
>>>
>>> Both outer Ls are part of what indicates the beginning
>>> and end of the loop, resp. So, as others said in this thread,
>>> there is syntactical ambiguity when using L with goto.
>>> The meaning of the goto L is not clear or agreed upon
>>> either, as readers here have said.
>>
>> Substitute "exit" for "goto" and reread your text.
> 
> When writing, I also thought about “return” and about
> exceptions, not just about “exit”. But none of them has
> the potential of driving the iterative process, they just
> leave it, the building block. It will be over.

So what? In either case actions are non-trivial because they potentially 
involve finalization of objects and types.

> loop is intended for the opposite, for when it’s not over yet.
> For when it’s done again. “exit” cannot mean that, but the
> hypothesized goto can.

1. "exit" can:

    exit when <condition>;

When condition evaluates false the loop continues.

2. "goto" cannot in any deeper sense than "exit" does because it is not 
"goto" which would drive the loop in this case.

>>> A loop statement is a means of controlling flow. So is goto.
>>> A loop controls iteration. Suppose that an additional
>>> goto is needed to express that. Then this thread will
>>> have discovered that Ada loops are deficient as building
>>> blocks of iteration.
>>
>> Substitute "if" for "goto".
> 
> Actually, “if” itself cannot directly make the program
> iterate, unlike “goto”.

Not in the case at hand.

P.S. Take if + a subroutine call. That gives recursion. Then following 
your flawed logic either if or loop is bad.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de