-- 求fact
function fact(n)
    if n == 0 then
        return 1
    else 
        return n* fact(n-1)
    end
end


print("Enter a number:")
a = io.read("*n")
print(fact(a))

--[[
statemetns;
]]

---[[
statemetns;
]]

a=1；
b=a+2;

a=1
b=a+2

type(nil)	 --> 			nil
type(true)	 --> 		  boolean
type(10.4 * 3)	 --> 	number
type("hi!")	 --> 			string
type(io.stdin)	 --> 	userdata
type(print)	 --> 			function
type(type)	 --> 			thread
type({})	 --> 				table
type(type(X))	 --> 	string	

x= x or v
--等价于
if not x then x = v end
(x>y) and x or y --表示选出x，y中的最大值

  1 == 1.0
  -3 == 3.0
  0.2e3 == 200 		

math.type(3) --> integer
math.type(3.0) --> float		

a = "hello"
print(#a)                             --> 5
print(#"good bye")       --> 8		

a= "hello"
a.."World"  -> "Hello World"

tonumber("3") --> 3
tonumber("10e") --> nil (not a valid number)
tonumber("100101",2) --> 37

[=[
a=b[c[i]]
]=]

a={}
a.x =10
a["x"] =12

a["10"] =3
a[10] =4

days = {"Sunday","Monday", "Tuesday"}	
a = {x=10, y=20}
a ={}; a.x=10;a.y=20;

opnames = {["+"]="add", ["-"]="sub", 
						["*"]="mul", ["/"]="div"}

{x=0, y=0} <--> {["x"]=0, ["y"]=0}
{"r", "g", "b"} <--> {[1]="r", [2]="g", [3]="b"}

t = {10, print, x=12, k="hi"}
for k, v in pairs(t) do
	print(k,v)
end

t = {10, print, 12, "hi"}
for k, v in ipairs(t) do
	print(k,v)
end

print "Hello world"
f {x=10, y = 20}

function incCount (n)
	n = n or 1
	globalCounter = globarCounter + n
end

function foo0 () end									-----返回0个结果
function foo1() return "a" end				------返回1个结果
function foo2() return "a", "b" end			----返回2个结果

x,y = foo2(),20  --x="a", y = 20
x,y = foo0(),20, 30   -- x=nil, y =20

t= {foo0(), foo2(), 4} -- t[1]=nil, t[2]="a", t[3]=4

print ((foo0())) --> nil
print ((foo1())) --> a
print ((foo2())) -->a	

function add(...)
    local s = 0
    for _, v in ipairs{...} do
        s = s + v 
    end
    return s
end
print (add(3,4,5,6,7))

function foo(...)
	local a, b ,c =...
end

function nonils (...)
    local arg = table.pack(...)
    for i=1, arg.n do
        if arg[i] == nil then return false end
    end
    return true
end    

print(nonils(2,3,nil))   -->false
print(nonils(2,3))  -->true

select(1, "a" , "b", "c")           -->a, b ,c
select(2, "a" , "b", "c")           -->b ,c
select(3, "a" , "b", "c")           -->,c
select("#", "a" , "b", "c")           -->3

function add(...)
    local s = 0
    for i=1, select("#", ...)do
        s = s + select(i, ...)
    end
    return s
end
print (add(3,4,5,6,7))

print (table.unpack{10,20,30})  --> 10,20,30
a,b = table.unpack{10,20,30}       --> a=10, b =20	

function f (x) x = x+1; return (x) end

return g(x) + 1
return x or g(x)
return (g(x))

return x[i].foo(x[j] + a* b, i +j)

io.write("sin(3) = ",math.sin(3), "\n")
io.write(string.format("sin(3) = %.4f\n", math.sin(3)))

local count = 0
for line in io.lines() do
	count = count + 1
	io.write(string.format("%6d ",count),line, "\n")
end

while true do
	local block = io.read(2^13)  -- 块大小是8kb
	if not block then break end
	io.write(block)
end	

print(io.open("/etc/passwd", "r")) 

local f = assert(io.open(filename, "r")) -- assert用来判断不是nil
local t = f:read("a")
f:close()

io.stdin; io.stdout; io.stderr
io.stderr::write(message)

local temp = io.input()		--- 保存当前输入流
io.input("newinput")		----打开一个新的当前输入流
(some operations)
io.input():close()					---关闭当前流
io.input(temp)						-- 回复此前的流

while i<=x do
	local x = i*2   --对于循环来说是局部的
	print(x)   -- 2,4,6,8....		
	i = i +1
end

function foo(x) return 2* x end
foo = function(x) return 2*x end

Lib={}
Lib.foo = function(x, y) return x+ y end
Lib.goo = function(x,y) return x-y emd

Lib={}
function Lib.foo(x,y)  return x+ y end
function Lib.goo(x,y) return x-y emd

local function f(params)
	body
end

local fact
fact = function(n)
	if n==0 then return 1
	else return n* fact(n-1)
	end
end

local function foo(params) body end
-- 被展开为：
local foo; foo = function(params) body end

s = "hello world"
i, j = string.find(s, "hello")
print(i,j)        ---> 1,5	

data = "Today is 17/7/1990"
d = string.match(date, "%d+/%d+/%d+")
print(d) --> 17/7/1990

s = string.gsub("add lii", "l", "x",1)
print(s)  --> axl lii

---找出 s中出现的所有单词
s = "some string"
words={}
for w in string.gmatch(s, "%a+") do
	words[#words + 1] = w
end

print((string.gsub("hello, up-down!", "%A",".")))
---> hello..up.down

pair = "name = Anna"
key, value = string.match(pair, "(%a)%s*=%s*(%a+)")
print(key, value) --> name ,Anna

> os.time({year=2015, month=8,  day=15, hour=12, min=45, sec=20})
	--> 1439653520

os.data("*t", 90600490)
--会返回一个表 *t 表示格式化字符串

print(os.date("a %A in %B")) --> a Tuesday in May
print(os.date("%d/%m/%Y"), 90600490)  --> 16/09/1998

local a={}		-----新数组
for i=1, 1000 do
	a[i] = 0
end

suqres= {1, 4, 9, 16};

local mt={}
for i=1, N do
	local row = {}
	mt[i] = row
	for j=1, M do
		row[j]=0
	end
end

list = nil
list = {next = list, value=v}
--- 遍历链表
local l = list
while l do
	visit l.value
	l = l.next
end

Entry{
	"Donald E Knuth",
	"Literate Programming",
	"CSLI",
	"1992"
}

Entry{
	"Donald E Knuth",
	"Literate Programming",
	"CSLI",
	"1992"
}

local count = 0
local authors = {}
function Entry(b)
	authors[b[1]] = true 
	count = count + 1
end
dofile("entry.txt")

function dofile(filename)
	local f = assert(loadfile(filename))
	return f()
end

f = load("i = i+1")
i=0
f(); print(i)   --> 1
f(); print(i)   --> 2

-- 下面两个语句等价
f = load("i=i+1")
f=function() i= i+1 end

load("a=1")
function(...) a=1 end

n = io.read()
assert(tonumber(n), "invalid input")

local status, err = pcal(function() error({code=121}) end)
print(err.code)  --> 121

function foo(str)
	if type(str) ~= "string" then
		error("string expected", 2)
	end
	--regular code
end

local m = require "math"
print(m.sin(3.14))

local M = {}

function M.add(c1, c2)
	return c1 + c2
end

-- 其他的一些函数

--最后返回模块
return M

local M = {}
package.loaded[...]  = M

local M = {}

function add(c1, c2)
	return c1 + c2
end

-- 其他的一些函数

--最后返回模块
return {
    add = add,
}

t = {}
print(getmetatable(t)) --> nil

--返回一个readoly的table，以传入的参数t为原型
function readOnly1(t)
    proxy = {}
    mt = {
        __index = t,
        __newindex = function(t, k, k) 
            error("attempt to update a read-only table",2)
        end
    }
    setmetatable(proxy, mt)
    return proxy
end

Account = {balance = 0}
function Account.withdraw(v)
	Account.balance = Account.balance - v
end

function Account.withdraw(self, v)
	self.balance = self.balance - v
end

a1 = Account; Account = nil
a1.withdraw(a1, 100.0)

a2 = {balance = 0, withdraw = Account.withdraw}
a2.withdraw(a2, 260)

function Account:withdraw( v)
	self.balance = self.balance - v
end
-- 也可以简化调用
a2:withdraw(260)  -- a2.withdraw(a2, 260)

setmetatable(A, {__index=B})

function Account:new(o)
	o = o or {}
	self.__index = self
	setmetatable(o, self)
	return o 
end

Account = {balance = 0}

function Account:new(o)
    -- body
    o = o or {}
    self.__index = self
    setmetatable(o, self)
    return o
end


function Account:deposit(v)
    self.balance = self.balance + v
end

function Account:withdraw(v)
    if v>self.balance then error "insufficient funds" end
    self.balance = self.balance - v
    -- body
end

SpecialAccount = Account:new()
s = SpecialAccount:new{limit = 1000.00}

function SepcialAccount:withdraw(v)
	..
end

a= "10"
print (a)   ---> 10
print (_G["a"])  -->10

setmetatable(_G, {
	__newindex = function(_, n)
		error("attempt to write to undeclared variable ".. n, 2)
		end,
		__index = function(_, n)
			error("attempt  to read undeclared variable" .. n ,2)
		end,
})

function declare(name, initval)
	rawset(_G, name. initval or false)
end

local z = 10
x  = y+z

local _ENV = some value
return function(...)
	local z = 10
	_ENV.x  = _ENV.y +z
end

co = coroutine.create(function() print("hi") end)
print (coroutine.status(co))   --- suspended

contine.resume(co)  --> hi

co = coroutine.create(function ()
	for i=1, 10 do
		print("co", i)
		coroutine.yield()
		end
	end)
	

co = coroutine.create(function (a, b, c)
	print("co",a,b,c+2)
	end)
coroutine.resume(co, 1,2,3) --> co  2 5

co = coroutine.create(function (a,b)
	coroutine.yield(a+b, a-b)
	end)
print(coroutine.resume(co, 20,10)) --> true 30 10