LUA 拾遗（函数）

（返回值）
        return arg[n]     -- 返回第n个返回值，index从1开始

（传参）

function  Window (options)
    -- check mandatory options
    if type(options.title) ~= "string" then
    error("no title" )
    elseif type(options.width) ~= "number" then
    error("no width" )
    elseif type(options.height) ~= "number" then
    error("no height")
    end
    print(options.title)
end

w = Window {
    x=0, y=0, width=300, height=200,
    title = "-- > mark" , background= "blue",
    border = true
}

（闭包）

function  newCounter()
  local i = 0
  return function () -- anonymous function
    i = i + 1
   return i
  end
end

c1 = newCounter()
print(c1()) --> 1
print(c1()) --> 2

关键在于理解upvalue（external local variable ）， 这个变量是每个闭包独有的且是静态的！

（强大的迭代器） -- 一般难写易用

function  allwords()
    local file = io.open("test.lua", "r")
    local  line = file:read() -- current line
    local  pos = 1 -- current position in the line
    return function () -- iterator function
        while  line do -- repeat while there are lines
            local s, e = string.find(line, "%w+" , pos)
            if s then -- found a word?
                pos = e + 1 -- next position is after this word
                return string.sub(line, s, e) -- return the word
            else
                line = file:read() -- word not found; try next line
                pos = 1 -- restart from first position
            end
        end
        file:close()
        return nil -- no more lines: end of traversal
    end
end

for word in allwords() do
    print(word)
end