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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: stopping a loop iteration without exiting it
Date: Thu, 4 Jan 2018 12:02:51 +0100
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Xref: reader02.eternal-september.org comp.lang.ada:49748
Date: 2018-01-04T12:02:51+01:00
List-Id: <comp.lang.ada>

On 2018-01-04 11:08, Jeffrey R. Carter wrote:
> On 01/04/2018 12:17 AM, Robert A Duff wrote:
>>
>> Jeff's suggestion (nested 'if' in the loop) is a good one when it works,
>> but it doesn't work when the "continue" is nested within further control
>> constructs.
> 
> I have never seen a real-world situation in which a "continue" was 
> needed. The vast majority of times that I've seen where people have 
> claimed they needed it, it could be replaced by an "if".

A typical case is a sequence of chained actions:

loop
    if This then
       Do_This;
       if That then
          Do_That;
          if More then
             Do_More
             if Even_More then
                Do_Even_More
                ...
             end if;
          end if;
       end if;
    end if;
end loop;

This cannot be handled without either:

1. Introducing a break-out exception
2. A Boolean guard/carry variable

Neither 1 nor 2 is really shining.

Now compare it to:

loop
    continue when not This;
    Do_This;
    continue when not That;
    Do_That;
    continue when not More;
    Do_More
    continue when not Even_More;
    Do_Even_More
    ...
end loop;

P.S. What I don't understand is why loop names cannot serve as labels. 
Why this:

loop
    ...
    goto Continue;
    ...
    <<Continue>>
end loop;

Instead of simple:

Process : loop
    ...
    goto Process;
    ...
end loop Process;

P.P.S. When-for-everyone is long overdue:

    goto <label> when <condition>;
    return [<result>] when <condition>;
    raise <exception> [with <message>] when <condition>;

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