改造Lua的debug.traceback()，让其显示栈上所有的局部变量

function tracebackex()  local ret = ""  local level = 2  ret = ret .. "stack traceback:\n"  while true do     --get stack info     local info = debug.getinfo(level, "Sln")     if not info then break end     if info.what == "C" then                -- C function      ret = ret .. tostring(level) .. "\tC function\n"     else           -- Lua function      ret = ret .. string.format("\t[%s]:%d in function `%s`\n", info.short_src, info.currentline, info.name or "")     end     --get local vars     local i = 1     while true do      local name, value = debug.getlocal(level, i)      if not name then break end      ret = ret .. "\t\t" .. name .. " =\t" .. tostringex(value, 3) .. "\n"      i = i + 1     end       level = level + 1  end  return ret  end    function tostringex(v, len)  if len == nil then len = 0 end  local pre = string.rep('\t', len)  local ret = ""  if type(v) == "table" then     if len > 5 then return "\t{ ... }" end     local t = ""     for k, v1 in pairs(v) do      t = t .. "\n\t" .. pre .. tostring(k) .. ":"      t = t .. tostringex(v1, len + 1)     end     if t == "" then      ret = ret .. pre .. "{ }\t(" .. tostring(v) .. ")"     else      if len > 0 then       ret = ret .. "\t(" .. tostring(v) .. ")\n"      end      ret = ret .. pre .. "{" .. t .. "\n" .. pre .. "}"     end  else     ret = ret .. pre .. tostring(v) .. "\t(" .. type(v) .. ")"  end  return ret  end