// look up a Lua value by its full name. If idx is 0, then this name
// is assumed to start in the global table, e.g. "string.gsub".
// With non-zero idx, can be used to look up subfields of a table
func Lookup(L *lua.State, path string, idx int) {
parts := strings.Split(path, ".")
if idx != 0 {
L.PushValue(idx)
} else {
L.GetGlobal("_G")
}
for _, field := range parts {
L.GetField(-1, field)
L.Remove(-2) // remove table
}
}