🌙

local name = "Lua"

name = "Lua"  -- avoid globals

local x = nil

local flag = true

local n = 42
local f = 3.14

local s = "Hello"
local s2 = 'World'

local arr = {1, 2, 3}  -- 1-indexed!

local t = {name = "Lua", version = 5.4}

type(x)  -- "nil", "number", "string", etc.

"Hello " .. "World"

#str

[[Multi
line
string]]

string.format("Hello, %s!", name)

string.upper(s)
string.lower(s)

string.sub(s, 1, 5)

string.find(s, "pattern")

string.gsub(s, "old", "new")

local t = {}
local arr = {1, 2, 3}
local dict = {a = 1, b = 2}

t[1]  -- array (1-indexed)
t.key or t["key"]  -- dict

t[1] = "first"
t.key = "value"

#t  -- only for array part

table.insert(t, value)
table.insert(t, 1, value)  -- at index

table.remove(t)  -- last
table.remove(t, 1)  -- at index

table.sort(t)
table.sort(t, function(a, b) return a > b end)

table.concat(t, ", ")

for i, v in ipairs(arr) do
  print(i, v)
end

for k, v in pairs(t) do
  print(k, v)
end

for i = 1, #t do
  print(t[i])
end

if x > 0 then
  print("positive")
elseif x < 0 then
  print("negative")
else
  print("zero")
end

-- Only nil and false are falsy
-- 0 and "" are truthy!

local x = a or default
local y = condition and a or b

while condition do
  -- code
end

repeat
  -- code
until condition

for i = 1, 10 do
  print(i)
end
for i = 10, 1, -1 do  -- step
  print(i)
end

while true do
  if condition then break end
end

local function add(a, b)
  return a + b
end

local add = function(a, b)
  return a + b
end

local function minmax(t)
  return math.min(unpack(t)), math.max(unpack(t))
end
local min, max = minmax({1, 2, 3})

local function sum(...)
  local args = {...}
  local total = 0
  for _, v in ipairs(args) do
    total = total + v
  end
  return total
end

local function greet(name)
  name = name or "World"
  print("Hello, " .. name)
end

local function counter()
  local count = 0
  return function()
    count = count + 1
    return count
  end
end
local c = counter()
c()  -- 1
c()  -- 2

local Person = {}
Person.name = "John"
function Person:greet()
  print("Hello, " .. self.name)
end

function Person:new(name)
  local obj = {name = name}
  setmetatable(obj, {__index = self})
  return obj
end
local p = Person:new("Alice")

p:greet()  -- self is p
p.greet(p) -- equivalent

local Student = {}
setmetatable(Student, {__index = Person})
function Student:new(name, grade)
  local obj = Person:new(name)
  obj.grade = grade
  setmetatable(obj, {__index = self})
  return obj
end

setmetatable(t, mt)

getmetatable(t)

mt.__index = function(t, k)
  return default
end

mt.__newindex = function(t, k, v)
  rawset(t, k, v)
end

mt.__tostring = function(t)
  return "MyObject"
end

mt.__add = function(a, b)
  return a.value + b.value
end

-- mymodule.lua
local M = {}

function M.hello()
  print("Hello")
end

return M

local mymod = require("mymodule")
mymod.hello()

package.path = package.path .. ";./lib/?.lua"

print("Hello")
io.write("No newline")

math.abs(x)
math.floor(x)
math.ceil(x)
math.random()
math.sin(x), math.cos(x)

os.time()
os.date()
os.execute("command")
os.getenv("PATH")

local f = io.open("file.txt", "r")
local content = f:read("*all")
f:close()

local f = io.open("file.txt", "w")
f:write("content")
f:close()