Namespaces And Modules

wiki

There is a Lua technical note which dicusses modules and packages [1].

Executing Lua files in a namespace

String = {}
dofile("stringlib.lua",String)
x = String.strlen("a string")

function dofile(f,t)
  local globals=globals
  local g=globals(t)
  local rc=%dofile(f)
  globals(g)
  return rc
end

"Global" keyword

(lhf) If you're willing to use a "global" declaration, then something very similar can be done right now: Instead of a "global" keyword, use a "global" function, with the syntax:

global "myvar" -- one name only

global{"a","b"} -- several names

do
  local G={}
  function global(x)
    if type(x)=="string" then
      %G[x]=1
    else
      for i,v in x do
        %G[v]=1
      end
    end
  end
end

You can now implement the semantics you want by setting tag methods for "setglobal" and/or "getglobal" that checks the name against G.

Thus to implement the need-declaration-to-write-to-globals semantics, set the "setglobal" tag method and raise an error if the given variable is not in G. The error will be show as soon as it happens; ie no sleeper!

For details, see the FAQ on uninitialized and read-only variables.

The problem with this approach is that declarations last for ever, not only for the current block.

(ET) Or the simple way:

global = globals()
...
global.x = 1
print(global.y)