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

[Dirk Laurie <dpl@...>]

On Thu, Jan 27, 2011 at 06:42:13PM +0200, Roberto Ierusalimschy 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.
> 

You don't need that second colon. Since do, break and end are 
keywords, do:foo, break:foo and end:foo can't be ambiguous.

Spaces around the first colon could be optional. Some might argue 
that they improve readability.  

I like the idea of other marks for break.  Particularly, '<' and '>'.
break<foo -- resume just before end:foo (i.e. continue)
break>foo -- resume just after end:foo 

This idea puts the emphasis on the label at 'end'; the label at
'do' seems not to be inevitable.  I'd hate to debug programs that
don't have the 'do' labels, though.  Those labels behave like
local declarations.  So basically I support the idea that labels 
should occur in pairs.

What about an optional label on 'end' that belongs to 'function'?
VIM does it by color :-)  Or label pairs on then...end?  No semantic 
meaning, but useful for checking logic in a tortuous program.

Dirk