It's trace tool for lua.
You can use trace.trace("varname") to trace the code execute. For example, if you run "lua main.lua" , you may got
main.lua : 12
main.lua : 4
n local 100
main.lua : 7
main.lua : 4
n local 99
main.lua : 7
main.lua : 4
n local 98
main.lua : 7
main.lua : 13
n global nil
s local 9.3326215443944e+157
http://blog.codingnow.com/2012/02/lua_trace.html (In Chinese)