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)