Functions

A function is a reusable block of code that you can call by name. Instead of writing the same logic in multiple places, you write it once as a function and call it whenever you need it.

Declaring and Calling Functions

Here's the basic syntax:

local function greet()
    print("Hello!")
end

greet() -- Hello!

You define the function with local function, give it a name, write the body, and close it with end. Then you call it by writing its name followed by ().

Parameters

Parameters let you pass values into a function:

local function greet(name: string)
    print(`Hello, {name}!`)
end

greet("Luau") -- Hello, Luau!
greet("World") -- Hello, World!

You can have as many parameters as you need:

local function add(a: number, b: number)
    print(a + b)
end

add(3, 7)  -- 10
add(10, 5) -- 15

Return Values

Functions can send a value back to whoever called them using return:

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

local result = add(3, 7)
print(result) -- 10

Notice the : number after the parameter list — that's the return type annotation, telling Luau what type this function is expected to return.

Luau also supports returning multiple values at once, which is something not many languages do:

local function minmax(a: number, b: number): (number, number)
    return math.min(a, b), math.max(a, b)
end

local min, max = minmax(10, 3)
print(min, max) -- 3  10

Default-like Behavior with or

Luau doesn't have built-in default parameters, but you can achieve the same thing using the or pattern:

local function greet(name: string?)
    name = name or "stranger"
    print(`Hello, {name}!`)
end

greet("Luau")  -- Hello, Luau!
greet()        -- Hello, stranger!

Since calling a function without an argument makes that parameter nil, and nil is falsy, the or kicks in and provides the fallback value.

Functions as Values

In Luau, functions are values just like numbers or strings. You can assign them to variables, pass them to other functions, or store them in tables:

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

local operation = add
print(operation(3, 7)) -- 10

This is a powerful idea that becomes especially useful as your programs grow in complexity.