Functions in Lua: The Building Blocks of Programs

What Are Functions?

A function is a named block of code that performs a specific task. You can call it whenever you need that task performed.

Functions allow you to:

• • Reuse code without repetition
• • Organize complex logic into manageable pieces
• • Test and debug smaller units of code
• • Create modular, maintainable programs

Defining a Function

Basic Syntax

function functionName()
    -- code to execute
end

Example

function greet()
    print("Hello, World!")
end

greet() -- Outputs: Hello, World!

Function Parameters

Parameters let you pass data into functions.

function greet(name)
    print("Hello, " .. name .. "!")
end

greet("Alice") -- Outputs: Hello, Alice!
greet("Bob")   -- Outputs: Hello, Bob!

Multiple Parameters

function add(a, b)
    print(a + b)
end

add(5, 3)  -- Outputs: 8
add(10, 20) -- Outputs: 30

Return Values

Functions can return values using the return keyword.

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

local result = add(5, 3)
print(result) -- Outputs: 8

Multiple Return Values

Lua functions can return multiple values at once!

function getMinMax(a, b)
    if a < b then
        return a, b
    else
        return b, a
    end
end

local min, max = getMinMax(10, 5)
print(min, max) -- Outputs: 5  10

You can ignore return values by not assigning them.

Local vs Global Functions

By default, functions are global. Use local to limit scope.

Global Function

function globalFunc()
    print("I'm global")
end

Local Function

local function localFunc()
    print("I'm local")
end

Anonymous Functions

Functions don't need names! They can be assigned to variables or passed as arguments.

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

greet("World") -- Outputs: Hello, World

Variable Arguments (Varargs)

Use ... to accept any number of arguments.

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

print(sum(1, 2, 3, 4, 5)) -- Outputs: 15

Functions as First-Class Values

In Lua, functions are first-class values. This means:

• • They can be stored in variables
• • They can be passed as arguments
• • They can be returned from other functions
• • They can be stored in tables

-- Storing in a table
local operations = {
    add = function(a, b) return a + b end,
    sub = function(a, b) return a - b end
}

print(operations.add(5, 3)) -- Outputs: 8

Common Function Mistakes

• Forgetting to call the function with ()
• Not handling nil parameters
• Ignoring return values
• Creating global functions accidentally
• Forgetting end keyword