Programming Language

Lua

Overview

Lua is a lightweight and fast embedded scripting language used in game development, embedded systems, and configuration scripts.

Details

Lua is a lightweight programming language developed by a Brazilian research group in 1993. "Lua" means "moon" in Portuguese. Despite being a very small interpreter of only a few dozen kilobytes, it is known for its powerful capabilities. Implemented in C, it can be easily embedded into C/C++ applications, making it primarily used as an extension language for other applications. It is particularly popular in the gaming industry, being used in many famous games such as World of Warcraft, Angry Birds, and Roblox. It features simple and intuitive syntax, dynamic typing, automatic memory management, and powerful table functionality, achieving high performance despite its small footprint. It is utilized in a wide range of fields including embedded systems, configuration files, and network device scripts.

Usage Examples

Hello World

-- Basic output
print("Hello, World!")

-- Multiple value output
print("Hello,", "Lua!")

-- Output using variables
local message = "Hello, Lua!"
print(message)

-- String concatenation
local name = "John"
local age = 25
print("My name is " .. name .. " and I am " .. age .. " years old.")

-- Formatted string using string.format
local formatted = string.format("My name is %s and I am %d years old.", name, age)
print(formatted)

-- Function example
function greet(name)
    return "Hello, " .. name .. "!"
end

print(greet("Smith"))

-- Local function
local function createMessage(name, age)
    return string.format("Name: %s, Age: %d", name, age)
end

print(createMessage("Johnson", 30))

-- Multi-line string
local multiline = [[
This is a multi-line
string.
In Lua, use [[]] to enclose.
]]
print(multiline)

-- Conditional output
local debug = true
if debug then
    print("Debug mode is enabled")
end

-- Loop example
for i = 1, 5 do
    print("Hello " .. i .. " times!")
end

-- Table example
local fruits = {"apple", "banana", "orange"}
for i, fruit in ipairs(fruits) do
    print(i .. ". " .. fruit)
end

-- Time display
print("Current time: " .. os.date("%Y-%m-%d %H:%M:%S"))

-- File output example
local function writeToFile()
    local file = io.open("hello.txt", "w")
    if file then
        file:write("Hello, World from Lua!\n")
        file:write("Multi-language support available\n")
        file:close()
        print("Written to file: hello.txt")
    else
        print("Failed to create file")
    end
end

writeToFile()

-- Execution as standalone script
if arg and arg[0] then
    print("Script file: " .. arg[0])
    if arg[1] then
        print("Argument 1: " .. arg[1])
    end
end

Variables and Data Types

-- Lua has local and global variables
-- Without 'local' keyword, variables become global

-- Basic data types
local stringValue = "string"
local numberValue = 42
local floatValue = 3.14159
local booleanValue = true
local nilValue = nil

print("=== Basic Data Types ===")
print("String:", stringValue, type(stringValue))
print("Integer:", numberValue, type(numberValue))
print("Float:", floatValue, type(floatValue))
print("Boolean:", booleanValue, type(booleanValue))
print("Nil:", nilValue, type(nilValue))

-- In Lua, integers and floats are not distinguished (distinguishable from Lua 5.3+)
local int = 10
local float = 10.0
print("Is integer?:", math.type and math.type(int) or "number")
print("Is float?:", math.type and math.type(float) or "number")

-- String operations
local str1 = "Hello"
local str2 = "World"
local combined = str1 .. " " .. str2  -- String concatenation
print("Concatenated:", combined)
print("Length:", #combined)
print("Uppercase:", string.upper(combined))
print("Lowercase:", string.lower(combined))
print("Substring:", string.sub(combined, 1, 5))
print("Replace:", string.gsub(combined, "World", "Lua"))

-- String to number conversion
local numStr = "123"
local strNum = 456
print("String→Number:", tonumber(numStr), type(tonumber(numStr)))
print("Number→String:", tostring(strNum), type(tostring(strNum)))

-- Escape sequences
local escaped = "Newline\n Tab\t Quote\" Backslash\\"
print("Escaped string:")
print(escaped)

-- Long string literals
local longString = [[
Multi-line
long string
can be written.
Escape characters are ignored: \n \t \"
]]
print("Long string:", longString)

-- Tables (Lua's most important data structure)
print("\n=== Tables ===")

-- Used as arrays
local array = {10, 20, 30, 40, 50}
print("Array:")
for i = 1, #array do  -- Lua arrays start from 1
    print("  [" .. i .. "] = " .. array[i])
end

-- Used as dictionary (hash table)
local dict = {
    name = "John Doe",
    age = 25,
    city = "New York",
    isActive = true
}

print("\nDictionary:")
for key, value in pairs(dict) do
    print("  " .. key .. " = " .. tostring(value))
end

-- Mixed table (array and dictionary features simultaneously)
local mixed = {
    "First element",  -- [1]
    "Second element",  -- [2]
    name = "Mixed table",
    count = 2
}

print("\nMixed table:")
print("  [1] =", mixed[1])
print("  [2] =", mixed[2])
print("  name =", mixed.name)
print("  count =", mixed.count)

-- Nested tables
local nested = {
    personal = {
        name = "Jane Smith",
        age = 30
    },
    work = {
        company = "Sample Company",
        position = "Engineer"
    },
    hobbies = {"reading", "movies", "programming"}
}

print("\nNested table:")
print("  Name:", nested.personal.name)
print("  Age:", nested.personal.age)
print("  Company:", nested.work.company)
print("  Hobbies:")
for i, hobby in ipairs(nested.hobbies) do
    print("    " .. i .. ". " .. hobby)
end

-- Dynamic table manipulation
local dynamic = {}
dynamic.name = "Dynamic table"
dynamic[1] = "First element"
dynamic["key with spaces"] = "Key with spaces"

-- table.insert and table.remove
table.insert(dynamic, "Added element")
table.insert(dynamic, 2, "Inserted at position 2")

print("\nDynamic table:")
for k, v in pairs(dynamic) do
    print("  " .. tostring(k) .. " = " .. tostring(v))
end

-- Variable scope
globalVar = "Global variable"  -- No 'local'

do
    local localVar = "Local variable"
    print("\nScope test:")
    print("  Inside block - Global:", globalVar)
    print("  Inside block - Local:", localVar)
end

print("Outside block - Global:", globalVar)
-- print("Outside block - Local:", localVar)  -- Would cause error

-- Multiple assignment
local a, b, c = 1, 2, 3
local x, y = "Hello", "World"
print("\nMultiple assignment:")
print("a, b, c =", a, b, c)
print("x, y =", x, y)

-- Value swapping
a, b = b, a
print("After swap: a, b =", a, b)

-- Multiple return values from function
local function getNameAge()
    return "Bob Johnson", 35
end

local name, age = getNameAge()
print("Multiple return values:", name, age)

-- Weak reference tables (garbage collection related)
local weak = {}
setmetatable(weak, {__mode = "v"})  -- Make values weak references
weak[1] = {data = "test data"}
print("\nWeak reference table created")

Functions and Control Structures

-- Basic function definition
function add(a, b)
    return a + b
end

-- Local function
local function multiply(a, b)
    return a * b
end

-- Anonymous function (function literal)
local subtract = function(a, b)
    return a - b
end

print("=== Basic Functions ===")
print("Addition:", add(5, 3))
print("Multiplication:", multiply(4, 6))
print("Subtraction:", subtract(10, 3))

-- Variadic function
local function sum(...)
    local args = {...}  -- Convert varargs to table
    local total = 0
    for i = 1, #args do
        total = total + args[i]
    end
    return total
end

print("Variadic sum:", sum(1, 2, 3, 4, 5))

-- Variadic argument processing using select
local function printArgs(...)
    print("Number of arguments:", select("#", ...))
    for i = 1, select("#", ...) do
        print("  Arg" .. i .. ":", select(i, ...))
    end
end

print("\nVariadic test:")
printArgs("Hello", "World", 123, true)

-- Multiple return values
local function getMinMax(...)
    local args = {...}
    if #args == 0 then return nil, nil end
    
    local min, max = args[1], args[1]
    for i = 2, #args do
        if args[i] < min then min = args[i] end
        if args[i] > max then max = args[i] end
    end
    return min, max
end

local minimum, maximum = getMinMax(5, 2, 8, 1, 9, 3)
print("\nMin・Max:", minimum, maximum)

-- Closures (functions within functions)
local function createCounter(initial)
    local count = initial or 0
    return function()
        count = count + 1
        return count
    end
end

local counter1 = createCounter(0)
local counter2 = createCounter(100)

print("\nClosure test:")
print("Counter1:", counter1(), counter1(), counter1())  -- 1, 2, 3
print("Counter2:", counter2(), counter2())              -- 101, 102

-- Higher-order functions (functions that take functions as arguments)
local function applyToArray(arr, func)
    local result = {}
    for i, v in ipairs(arr) do
        result[i] = func(v)
    end
    return result
end

local numbers = {1, 2, 3, 4, 5}
local doubled = applyToArray(numbers, function(x) return x * 2 end)
local squared = applyToArray(numbers, function(x) return x * x end)

print("\nHigher-order functions:")
print("Original array:", table.concat(numbers, ", "))
print("Doubled:", table.concat(doubled, ", "))
print("Squared:", table.concat(squared, ", "))

-- Conditional statements
print("\n=== Conditional Statements ===")

local score = 85

if score >= 90 then
    print("Excellent")
elseif score >= 80 then
    print("Good")
elseif score >= 70 then
    print("Average")
elseif score >= 60 then
    print("Needs Improvement")
else
    print("Failed")
end

-- Alternative to ternary operator (using and/or operators)
local grade = score >= 60 and "Pass" or "Fail"
print("Result:", grade)

-- Loop structures
print("\n=== Loop Structures ===")

-- Numeric for loop
print("Numeric for loop:")
for i = 1, 5 do
    print("  Count:", i)
end

print("For loop with step:")
for i = 10, 2, -2 do  -- From 10 to 2 with step -2
    print("  Reverse:", i)
end

-- Generic for loop (iterator)
local fruits = {"apple", "banana", "orange", "strawberry"}

print("Using ipairs (with index):")
for index, fruit in ipairs(fruits) do
    print("  " .. index .. ": " .. fruit)
end

local person = {name = "Smith", age = 30, city = "London"}

print("Using pairs (key-value):")
for key, value in pairs(person) do
    print("  " .. key .. " = " .. tostring(value))
end

-- While loop
print("While loop:")
local count = 1
while count <= 3 do
    print("  while:", count)
    count = count + 1
end

-- Repeat loop (equivalent to do-while)
print("Repeat loop:")
count = 1
repeat
    print("  repeat:", count)
    count = count + 1
until count > 3

-- Break and control structures
print("Using break statement:")
for i = 1, 10 do
    if i == 5 then
        print("  Break at 5")
        break
    end
    print("  Value:", i)
end

-- Goto statement (Lua 5.2+)
print("Goto example:")
local i = 1
::loop::
if i <= 3 then
    print("  goto:", i)
    i = i + 1
    goto loop
end

-- Error handling
print("\n=== Error Handling ===")

-- Safe function call using pcall (protected call)
local function riskyFunction(x)
    if x == 0 then
        error("Zero is not allowed")
    end
    return 10 / x
end

local success, result = pcall(riskyFunction, 5)
if success then
    print("Success:", result)
else
    print("Error:", result)
end

local success, result = pcall(riskyFunction, 0)
if success then
    print("Success:", result)
else
    print("Error:", result)
end

-- xpcall (extended pcall) with error handler
local function errorHandler(err)
    return "Handled by error handler: " .. tostring(err)
end

local success, result = xpcall(function() return riskyFunction(0) end, errorHandler)
print("xpcall result:", success, result)

-- Assert function
local function validateAge(age)
    assert(type(age) == "number", "Age must be a number")
    assert(age >= 0 and age <= 150, "Age must be between 0 and 150")
    return age
end

local validAge = validateAge(25)
print("Valid age:", validAge)

-- Invalid age test (commented out)
-- local invalidAge = validateAge("abc")  -- Would cause error

Tables and Metatables

-- One of Lua's most powerful features: Metatables

print("=== Advanced Table Operations ===")

-- Basic table operations
local array = {10, 20, 30}
print("Original array:", table.concat(array, ", "))

-- Element addition
table.insert(array, 40)        -- Add to end
table.insert(array, 2, 15)     -- Insert at position 2
print("After addition:", table.concat(array, ", "))

-- Element removal
local removed = table.remove(array, 2)  -- Remove 2nd element
print("Removed element:", removed)
print("After removal:", table.concat(array, ", "))

-- Sorting
local unsorted = {3, 1, 4, 1, 5, 9, 2, 6}
table.sort(unsorted)
print("After sort:", table.concat(unsorted, ", "))

-- Custom sorting
local names = {"Smith", "Johnson", "Brown", "Davis"}
table.sort(names, function(a, b) return #a < #b end)  -- Sort by length
print("Sort by length:", table.concat(names, ", "))

-- Metatable basics
print("\n=== Metatables ===")

-- Simple metatable example
local mt = {
    __add = function(a, b)
        return {x = a.x + b.x, y = a.y + b.y}
    end,
    __tostring = function(t)
        return string.format("Point(%d, %d)", t.x, t.y)
    end,
    __index = function(t, key)
        if key == "magnitude" then
            return math.sqrt(t.x^2 + t.y^2)
        end
        return nil
    end
}

local point1 = {x = 3, y = 4}
local point2 = {x = 1, y = 2}

setmetatable(point1, mt)
setmetatable(point2, mt)

-- Using metamethods
local point3 = point1 + point2  -- __add metamethod
print("Point addition:", tostring(point3))  -- __tostring metamethod
print("point1 magnitude:", point1.magnitude)  -- __index metamethod

-- Class-like objects
print("\n=== Object-Oriented Programming ===")

-- Person class definition
local Person = {}
Person.__index = Person

function Person:new(name, age)
    local obj = {
        name = name or "Unknown",
        age = age or 0
    }
    setmetatable(obj, self)
    return obj
end

function Person:introduce()
    return string.format("My name is %s and I am %d years old.", self.name, self.age)
end

function Person:haveBirthday()
    self.age = self.age + 1
    print(self.name .. ", happy " .. self.age .. "th birthday!")
end

function Person:__tostring()
    return string.format("Person{name='%s', age=%d}", self.name, self.age)
end

-- Object creation and usage
local person1 = Person:new("John Doe", 25)
local person2 = Person:new("Jane Smith", 30)

print("person1:", person1:introduce())
print("person2:", person2:introduce())

person1:haveBirthday()
print("After birthday:", tostring(person1))

-- Inheritance example
local Student = {}
Student.__index = Student
setmetatable(Student, Person)  -- Inheritance from Person to Student

function Student:new(name, age, school)
    local obj = Person.new(self, name, age)
    obj.school = school or "Unspecified"
    setmetatable(obj, self)
    return obj
end

function Student:introduce()
    local base = Person.introduce(self)
    return base .. " I study at " .. self.school .. "."
end

function Student:study(subject)
    print(self.name .. " is studying " .. subject .. ".")
end

local student = Student:new("Bob Johnson", 20, "MIT")
print("Student introduction:", student:introduce())
student:study("Mathematics")

-- Proxy table (controlling property access)
print("\n=== Proxy Tables ===")

local function createReadOnlyTable(t)
    local proxy = {}
    local mt = {
        __index = t,
        __newindex = function(table, key, value)
            error("Writing to read-only table is forbidden")
        end
    }
    setmetatable(proxy, mt)
    return proxy
end

local config = {
    version = "1.0",
    author = "Developer",
    debug = true
}

local readOnlyConfig = createReadOnlyTable(config)
print("Version:", readOnlyConfig.version)
print("Author:", readOnlyConfig.author)

-- Write test (would cause error)
-- readOnlyConfig.version = "2.0"  -- Error

-- Property access monitoring
local function createWatchedTable()
    local data = {}
    local watchers = {}
    
    local mt = {
        __index = data,
        __newindex = function(t, key, value)
            local oldValue = data[key]
            data[key] = value
            
            -- Notify watchers
            for _, watcher in ipairs(watchers) do
                watcher(key, oldValue, value)
            end
        end
    }
    
    local proxy = {}
    setmetatable(proxy, mt)
    
    -- Add watcher method
    proxy.addWatcher = function(watcher)
        table.insert(watchers, watcher)
    end
    
    return proxy
end

local watched = createWatchedTable()
watched.addWatcher(function(key, oldVal, newVal)
    print(string.format("Property change: %s = %s → %s", 
          key, tostring(oldVal), tostring(newVal)))
end)

watched.name = "Test"
watched.count = 1
watched.count = 2

Modules and Packages

-- Module system in Lua

print("=== Module Basics ===")

-- Simple module creation example
local mymath = {}

function mymath.add(a, b)
    return a + b
end

function mymath.multiply(a, b)
    return a * b
end

mymath.pi = 3.14159

-- Private function (not accessible from outside module)
local function privateHelper(x)
    return x * 2
end

function mymath.doubleAndAdd(a, b)
    return privateHelper(a) + b
end

-- Module usage
print("mymath.add(5, 3):", mymath.add(5, 3))
print("mymath.multiply(4, 6):", mymath.multiply(4, 6))
print("mymath.pi:", mymath.pi)
print("mymath.doubleAndAdd(5, 3):", mymath.doubleAndAdd(5, 3))

-- Advanced module patterns
print("\n=== Advanced Module Patterns ===")

-- Module with namespaces
local utils = {}

utils.string = {}
utils.table = {}
utils.math = {}

-- String utilities
function utils.string.trim(s)
    return s:gsub("^%s*(.-)%s*$", "%1")
end

function utils.string.split(str, delimiter)
    local result = {}
    local pattern = string.format("([^%s]+)", delimiter)
    for match in str:gmatch(pattern) do
        table.insert(result, match)
    end
    return result
end

-- Table utilities
function utils.table.deepCopy(orig)
    local copy
    if type(orig) == 'table' then
        copy = {}
        for orig_key, orig_value in next, orig, nil do
            copy[utils.table.deepCopy(orig_key)] = utils.table.deepCopy(orig_value)
        end
        setmetatable(copy, utils.table.deepCopy(getmetatable(orig)))
    else
        copy = orig
    end
    return copy
end

function utils.table.isEmpty(t)
    return next(t) == nil
end

-- Math utilities
function utils.math.clamp(value, min, max)
    return math.max(min, math.min(max, value))
end

function utils.math.lerp(a, b, t)
    return a + (b - a) * t
end

-- Utility usage examples
print("String trim:", "'" .. utils.string.trim("  hello world  ") .. "'")

local parts = utils.string.split("apple,banana,orange", ",")
print("String split:")
for i, part in ipairs(parts) do
    print("  " .. i .. ": " .. part)
end

local original = {a = 1, b = {c = 2, d = 3}}
local copied = utils.table.deepCopy(original)
copied.b.c = 999
print("Original table b.c:", original.b.c)  -- 2 (unchanged)
print("Copied table b.c:", copied.b.c)  -- 999

print("clamp(15, 0, 10):", utils.math.clamp(15, 0, 10))
print("lerp(0, 100, 0.5):", utils.math.lerp(0, 100, 0.5))

-- Factory pattern
print("\n=== Factory Pattern ===")

local function createLogger(name)
    local logger = {}
    
    function logger.info(message)
        print(string.format("[INFO][%s] %s", name, message))
    end
    
    function logger.warn(message)
        print(string.format("[WARN][%s] %s", name, message))
    end
    
    function logger.error(message)
        print(string.format("[ERROR][%s] %s", name, message))
    end
    
    return logger
end

local appLogger = createLogger("App")
local dbLogger = createLogger("Database")

appLogger.info("Application started")
dbLogger.warn("Connection is slow")
appLogger.error("Unexpected error")

-- Singleton pattern
print("\n=== Singleton Pattern ===")

local ConfigManager = {}
local instance = nil

function ConfigManager.getInstance()
    if not instance then
        instance = {
            settings = {},
            
            set = function(self, key, value)
                self.settings[key] = value
            end,
            
            get = function(self, key, default)
                return self.settings[key] or default
            end,
            
            dump = function(self)
                print("Configuration:")
                for k, v in pairs(self.settings) do
                    print("  " .. k .. " = " .. tostring(v))
                end
            end
        }
    end
    return instance
end

-- Singleton usage
local config1 = ConfigManager.getInstance()
local config2 = ConfigManager.getInstance()

config1:set("debug", true)
config2:set("version", "1.0")

print("config1 and config2 same instance?", config1 == config2)
config1:dump()

-- Package loader simulation
print("\n=== Package System Simulation ===")

local packageSystem = {}
packageSystem.loaded = {}

function packageSystem.require(name)
    if packageSystem.loaded[name] then
        return packageSystem.loaded[name]
    end
    
    -- In actual system, would load from files
    local module
    if name == "json" then
        module = {
            encode = function(t) return "JSON encoded: " .. tostring(t) end,
            decode = function(s) return {decoded = s} end
        }
    elseif name == "http" then
        module = {
            get = function(url) return "HTTP GET: " .. url end,
            post = function(url, data) return "HTTP POST to " .. url end
        }
    else
        error("Module '" .. name .. "' not found")
    end
    
    packageSystem.loaded[name] = module
    return module
end

-- Package usage
local json = packageSystem.require("json")
local http = packageSystem.require("http")

print("JSON encode:", json.encode({test = "data"}))
print("HTTP GET:", http.get("http://example.com"))

-- Second require returns already loaded module
local json2 = packageSystem.require("json")
print("Same instance?", json == json2)

File Operations and C Integration

-- File input/output operations

print("=== File Input/Output ===")

-- Writing to file
local function writeToFile()
    local filename = "test.txt"
    local file = io.open(filename, "w")
    
    if file then
        file:write("Hello, Lua!\n")
        file:write("This is a test file.\n")
        file:write("Current time: " .. os.date("%Y-%m-%d %H:%M:%S") .. "\n")
        
        -- Writing numeric data
        for i = 1, 5 do
            file:write(string.format("Number %d: %d\n", i, i * i))
        end
        
        file:close()
        print("File write completed: " .. filename)
        return true
    else
        print("Failed to create file")
        return false
    end
end

-- Reading from file
local function readFromFile()
    local filename = "test.txt"
    local file = io.open(filename, "r")
    
    if file then
        print("\nFile content:")
        print("=" .. string.rep("=", 30))
        
        -- Read entire content at once
        local content = file:read("*all")
        file:close()
        print(content)
        print("=" .. string.rep("=", 30))
        return true
    else
        print("Failed to read file")
        return false
    end
end

-- Line-by-line reading
local function readLineByLine()
    local filename = "test.txt"
    local file = io.open(filename, "r")
    
    if file then
        print("\nLine-by-line reading:")
        local lineNumber = 1
        for line in file:lines() do
            print(string.format("Line%d: %s", lineNumber, line))
            lineNumber = lineNumber + 1
        end
        file:close()
        return true
    else
        print("Failed to read file")
        return false
    end
end

-- Binary file operations
local function binaryFileOperations()
    local filename = "binary.dat"
    
    -- Binary write
    local file = io.open(filename, "wb")
    if file then
        -- Write some byte values
        for i = 0, 255, 17 do
            file:write(string.char(i))
        end
        file:close()
        print("Binary file created: " .. filename)
    end
    
    -- Binary read
    file = io.open(filename, "rb")
    if file then
        print("Binary file content:")
        local byte = file:read(1)
        local position = 1
        while byte do
            print(string.format("Position%d: %d (0x%02X)", position, string.byte(byte), string.byte(byte)))
            byte = file:read(1)
            position = position + 1
        end
        file:close()
    end
end

-- CSV file operations
local function csvOperations()
    local csvFile = "data.csv"
    
    -- CSV file creation
    local file = io.open(csvFile, "w")
    if file then
        file:write("Name,Age,Department,Salary\n")
        file:write("John Doe,25,Sales,300000\n")
        file:write("Jane Smith,30,Development,400000\n")
        file:write("Bob Johnson,35,Management,350000\n")
        file:close()
        print("CSV file created: " .. csvFile)
    end
    
    -- CSV reading and parsing
    file = io.open(csvFile, "r")
    if file then
        print("\nCSV data:")
        local header = file:read("*line")
        print("Header: " .. header)
        
        local rowNumber = 1
        for line in file:lines() do
            local fields = {}
            for field in line:gmatch("([^,]+)") do
                table.insert(fields, field)
            end
            
            print(string.format("Row%d: Name=%s, Age=%s, Dept=%s, Salary=%s", 
                  rowNumber, fields[1], fields[2], fields[3], fields[4]))
            rowNumber = rowNumber + 1
        end
        file:close()
    end
end

-- Execute file operations
if writeToFile() then
    readFromFile()
    readLineByLine()
end

binaryFileOperations()
csvOperations()

-- System information and OS operations
print("\n=== System Information ===")

print("OS time:", os.date("%Y-%m-%d %H:%M:%S"))
print("UTC time:", os.date("!%Y-%m-%d %H:%M:%S"))
print("Epoch time:", os.time())

-- Date calculation
local birthday = os.time{year=1990, month=5, day=15}
local now = os.time()
local ageInSeconds = now - birthday
local ageInDays = math.floor(ageInSeconds / (24 * 60 * 60))
print("Days since birthday:", ageInDays .. " days")

-- Environment variables (if they exist)
local home = os.getenv("HOME") or os.getenv("USERPROFILE")
if home then
    print("Home directory:", home)
end

local path = os.getenv("PATH")
if path then
    print("PATH environment variable length:", #path .. " characters")
end

-- Using C library functions
print("\n=== C Library Functions ===")

-- Math library
print("Math functions:")
print("sin(π/2):", math.sin(math.pi / 2))
print("cos(0):", math.cos(0))
print("sqrt(16):", math.sqrt(16))
print("log(math.e):", math.log(math.e))
print("random(1,10):", math.random(1, 10))

-- Random seed setting
math.randomseed(os.time())
print("Random array:")
local randomNumbers = {}
for i = 1, 5 do
    randomNumbers[i] = math.random(1, 100)
end
print("  " .. table.concat(randomNumbers, ", "))

-- String library
print("\nString functions:")
local testString = "Hello, Lua Programming!"
print("Original string:", testString)
print("Uppercase:", string.upper(testString))
print("Lowercase:", string.lower(testString))
print("String length:", string.len(testString))
print("Substring(8-10):", string.sub(testString, 8, 10))

-- Pattern matching
local email = "[email protected]"
local username, domain = string.match(email, "([^@]+)@([^@]+)")
print("Email parsing:")
print("  Username:", username)
print("  Domain:", domain)

-- String replacement
local text = "Today is sunny. Tomorrow will be sunny too."
local replaced = string.gsub(text, "sunny", "rainy")
print("Before replacement:", text)
print("After replacement:", replaced)

-- Table library
print("\nTable functions:")
local fruits = {"apple", "banana", "orange", "strawberry"}
print("Original array:", table.concat(fruits, ", "))

table.sort(fruits)
print("After sort:", table.concat(fruits, ", "))

local numbers = {3, 1, 4, 1, 5, 9, 2, 6}
table.sort(numbers, function(a, b) return a > b end)  -- Descending
print("Descending sort:", table.concat(numbers, ", "))

-- Simple C integration simulation (actual implementation requires C-side code)
print("\n=== C Integration Concepts ===")
print("In actual C integration, you can define functions like:")
print("- Implement high-speed computation functions in C")
print("- Call C functions from Lua")
print("- Execute Lua scripts from C")
print("- Provide C functions as shared libraries")

-- Example of using C extensions to complement Lua's limitations
local function simulateCExtension()
    print("\nTypical uses for C extensions:")
    print("1. Accelerating numerical computations")
    print("2. Accessing system APIs")
    print("3. Leveraging existing C libraries")
    print("4. Memory-intensive processing")
    print("5. Real-time processing")
end

simulateCExtension()

Advantages and Disadvantages

Advantages

• Lightweight: Very small memory footprint (few dozen KB)
• High Performance: Fast execution despite compact size
• Easy Embedding: Simple integration into C/C++ applications
• Simple Syntax: Easy to learn and readable code
• Flexible Data Structures: Unified arrays/dictionaries/objects through tables
• Metaprogramming: Powerful feature extension through metatables

Disadvantages

• Limited Ecosystem: Minimal standard library
• Small Community: Smaller compared to other major languages
• Lack of Debug Tools: Limited development tools and IDE support
• 1-based Arrays: Different array indexing from most languages
• Global Variable Issues: Default global scope can be problematic
• Error Messages: Limited detailed information for runtime errors

Reference Links

Official Documentation

• Lua Official Site - Lua official website
• Lua Reference Manual - Official reference manual
• Programming in Lua - Official programming guide

Learning Resources

• Learn Lua in Y Minutes - Quick start guide
• Lua Tutorial - Basic tutorial
• Lua Users Wiki - Community wiki

Development Tools & Libraries

• LuaRocks - Lua package manager
• LÖVE 2D - Game development framework for Lua
• OpenResty - Lua utilization with Nginx
• Wireshark Lua - Wireshark protocol analysis

Use Cases & Frameworks

• Redis Lua Scripting - Script execution in Redis
• World of Warcraft Addons - WoW addon development
• Kong API Gateway - Lua plugins
• Roblox Lua - Game development platform