Re: [ANN] Lua 5.2.0 (beta-rc2) now available

[Gé Weijers <ge@...>]

On Wed, 2011-06-22 at 06:57 +0200, Lorenzo Donati wrote:
> I've already argued on the other thread (5.2 beta-rc1) that I'd prefer a 
> limit "per-block". There I motivated my preference with an use case for 
> error management.
> 

I agree. There are two possible restrictions that would work:

- your suggestion: allow one definition of a label per block. Algol
scope rules apply within a function:

	::label::
	do
		goto label -- should jump FORWARD

	::label::
	end

- disallow a definition of a label if that label is already visible in
the scope. The above example would be illegal, but the next one would be
ok:

	for i in something() do
		...
		goto continue
		...
		::continue:: This is a little tricky in a one-pass compiler:
	end
	for i in something() do
		...
		goto continue
		...
	::continue::
	end

Advantage: you can decide on the fly whether a jump is forward or
backward, and you disallow one label hiding another. This is a little
more restrictive, but your 'continue' example works.

Gé