Learn Lua in 15 Minutes中提到,require module的等价形式:

-- Another file can use mod.lua's functionality:
local mod = require('mod')  -- Run the file mod.lua.

-- require is the standard way to include modules.
-- require acts like:     (if not cached; see below)
local mod = (function ()
  <contents of mod.lua>
end)()
-- It's like mod.lua is a function body, so that
-- locals inside mod.lua are invisible outside it.

这个解释很好地说明了require module的原理,让人豁然开朗。