| -- make global variables readonly | |
| local f=function (t,i) error("cannot redefine global variable `"..i.."'",2) end | |
| local g={} | |
| local G=getfenv() | |
| setmetatable(g,{__index=G,__newindex=f}) | |
| setfenv(1,g) | |
| -- an example | |
| rawset(g,"x",3) | |
| x=2 | |
| y=1 -- cannot redefine `y' |