Functions

Define and call reusable code blocks.

Declaration

fun greet(name) {
    print "Hello, " + name + "!";
}

Call with parentheses:

greet("Alice");  // Hello, Alice!

Return Values

fun add(a, b) {
    return a + b;
}

var sum = add(3, 4);  // 7

Functions without return implicitly return nil.

First-Class Functions

Functions are values and can be:

• Stored in variables
• Passed as arguments
• Returned from other functions

fun makeGreeter(greeting) {
    fun greeter(name) {
        print greeting + ", " + name + "!";
    }
    return greeter;
}

var hello = makeGreeter("Hello");
hello("Alice");  // Hello, Alice!

Closures

Functions capture their enclosing environment:

fun makeCounter() {
    var count = 0;
    fun increment() {
        count = count + 1;
        return count;
    }
    return increment;
}

var counter = makeCounter();
print counter();  // 1
print counter();  // 2
print counter();  // 3

Each call to makeCounter() creates a new, independent counter.

Recursion

Functions can call themselves:

fun fibonacci(n) {
    if (n <= 1) return n;
    return fibonacci(n - 1) + fibonacci(n - 2);
}

print fibonacci(10);  // 55

Native Functions

Built-in functions:

var start = clock();
// ... some computation ...
var elapsed = clock() - start;
print "Elapsed: " + elapsed + " seconds";

Next Steps

• Classes → — Object-oriented programming