Re: I'd give my right arm for a continue statement

[Axel Kittenberger <axkibe@...>]

First let me thank you for openmindness to this issue!

I like the idea of labeled breaks, more power, nothihng really
breaking. However, I doubt if it really is a suitable replacement for
"continue".
When doing idioms around it, we should draft the "worst case" loop,
having one break and one continue.
So for a start I suppose labels to be after any do, since the existing
':' requires an L-Value, there should no breaks to be used when the
parser stack is empty.

With this the continue/break idiom would look like this:
for k, v in pairs(t) do :loop do:continue
   if condition then
     break :loop
  end
   if anotherCondition then
     break :continue
  end
end end

I don't know if this really is so good looking.

There should be some idiom that effectively allows you to express
"this code block is ended herby". For loops this would be equivalent
to a continue. Within Do-End block should  execution should resume
after the end.

Dirks suggeston for:
break<label
break>label
might be one way to achieve this, not yet convinced tough, especially
as the syntax should be valid without a label as well for the
innermost block.

The standard keyword across many languages has become "continue",
however It must not be that way, especially for do-end-blocks it would
be nice to have a keyword that matches this "get to the end" idea. I
don't know a good word, conclude? finish?

Kind regards,

On Thu, Jan 27, 2011 at 5:42 PM, Roberto Ierusalimschy
<roberto@inf.puc-rio.br> wrote:
>> > I believe that this "break N" will kill code readability as sure as
>> > "goto" would.
>>
>> Yeah, I would get lost pretty quick!  Named labels would help [...]
>
> If that could save Steve's right arm, we like the idea of break with
> labels.
>
> In Lua, we cannot have traditional labels, because the syntax "foo:"
> already has a different meaning. Instead, a simple syntax would be to
> add labels only to "do end" blocks, for instance like this:
>
>  do :label:
>    ...
>  end
>
> Then, a continue could be written like here:
>
>  while cond do
>    do :process_item:
>
>                    break :process_item:
>
>    end
>  end
>
> There are several details that could change (other mark instead
> of colons, whether the label after break needs marks, whether an
> optional [or mandatory] label could be added after the corresponding
> 'end', etc.), but the basic idea would not change much.
>
> -- Roberto
>
>
>