Re: Lua registry, environment, and threads.

["Juris Kalnins" <juris@...>]

On Tue, 12 Jan 2010 08:23:28 +0200, Juris Kalnins <juris@mt.lv> wrote

> do
>    a=1
>    do
>      a=2
>      g() -- access to a gives 2
>    end
>    -- a == 1
> end

ugh, correcting myself. what I wrote mixes up definitions and assignments,  
I should have written:

do a=1
  do dynamic a=2
    g() -- access to a gives 2
  end   -- a == 1
end

where 'dynamic' is like 'local' in perl :)
There are already many ways to do it right now. Usually code has to pass  
around some context as an
extra argument, and the above looks like:

do ctx.a=1
  do
    local prev_a = ctx.a
    ctx.a = 2
    g(ctx)
    ctx.a = prev_a
  end
end

You can even "smuggle" 'ctx' through functions that are not aware of it  
(e.g. gsub), by capturing it as
upvalue.
When writing parser or GUI code, there is a lot of such 'ctx' passing and  
value saving.
Dynamic scoping makes writing such code very natural.