Re: In praise of globals

[Philipp Janda <siffiejoe@...>]

Am 25.04.2013 01:32 schröbte Jay Carlson:
> [...]
>
> ===
> local a=7
> local a
> print(a)
> ===
>
> In this example it doesn't matter whether you paste this at the REPL or not. :-)

It does if you have a non-nil global "a".

> [...]
>
> I don't have any suggestions. But writing your code in localized style implies you either won't be *interacting* with it, or that you have a more sophisticated IDE than just an xterm.

My suggestion would be to make a proper interactive interpreter that 
respects the local environment. I have some ideas, but it is late, so 
maybe they are utter nonsense ...:

Assuming we have a valid chunk that can be compiled via load(string). If 
we have identified the locals in the previous chunk using something like 
lbci[*] we can do some source code transformation on the current chunk 
to add those locals at the beginning. Problem is, we need a way to save 
the locals at the end of a chunk, and we need to handle upvalues. I 
think we can solve both problems in one go:

We append something like "\n; return function() return a, b, c end", 
where `a`, `b`, `c` are the locals, to the end of the chunk, and get a 
function which we can query for the upvalue ids.

To load the next chunk `chunk2` we need to run something like

    return function( a, b, c )
      return function()
        <chunk2>
        ; return function() return a, b, c, d, e end
      end
    end()

to get a function that is equivalent to `chunk2` but uses upvalues for 
the locals `a`, `b`, and `c`. Now we can use debug.upvalueid and 
debug.upvaluejoin, to merge the upvalues of the function returned from 
the last chunk and this one.
And if that works, we can _finally_ get rid of "global by default" :-p ...

What do you think? Did I miss something?

> Jay

Good night,
Philipp


  [*]:  What is the status of lbci for Lua 5.2 by the way?