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Functions & Closures

Functions are the primary unit of code reuse in Kyna. They support typed parameters, return annotations, default values, and lexical closures.

1. Declaring Functions​

Use the fn keyword to declare a function:

fn calculateTax(amount: float, rate: float): float {
    return amount * rate;
}

const tax = calculateTax(150.0, 0.08);
print("Sales tax:", tax); # 12.0

2. Functions Without Return Values​

When a function performs side effects and returns nothing, omit the return type annotation:

fn logEvent(channel: str, message: str) {
    print("[" + channel + "]: " + message);
}

logEvent("AUTH", "User signed in successfully");

3. First-Class Functions & Closures​

Functions in Kyna are first-class values. You can assign them to variables, pass them as arguments to other functions, and return them:

fn createCounter(step: int) {
    var count = 0;
    
    # Inner closure capturing 'step' and 'count'
    return fn(): int {
        count = count + step;
        return count;
    };
}

const incrementByFive = createCounter(5);
print(incrementByFive()); # 5
print(incrementByFive()); # 10
print(incrementByFive()); # 15

4. Higher-Order Functions​

Functions that accept other functions enable expressive data transformations:

fn transform(val: int, op: fn(int): int): int {
    return op(val);
}

fn square(x: int): int {
    return x * x;
}

print("Transformed:", transform(7, square)); # 49

Next Steps​