Local variables in the main block are global

[Dirk Laurie <dirk.laurie@...>]

Try this:

~~~ file localisglobal.lua
setmetatable(_ENV,{__newindex = function (ENV,name,value)
   if name:match"^%a%d?$" then
      print(": A global name like '"..name.."' is asking for trouble")
   end
   rawset(ENV,name,value)
end})

local Y=2
~~~