// Higher-Order Functions and Closures
//
// Functions are first-class values in Lux.
// Closures capture their environment.
//
// Expected output:
// Square of 5: 25
// Cube of 3: 27
// Add 10 to 5: 15
// Add 10 to 20: 30
// Composed: 15625 (cube(square(5)) = cube(25) = 15625)

fn apply(f: fn(Int): Int, x: Int): Int = f(x)

fn compose(f: fn(Int): Int, g: fn(Int): Int): fn(Int): Int =
    fn(x: Int): Int => f(g(x))

fn square(n: Int): Int = n * n

fn cube(n: Int): Int = n * n * n

fn makeAdder(n: Int): fn(Int): Int =
    fn(x: Int): Int => x + n

fn main(): Unit with {Console} = {
    // Apply functions
    Console.print("Square of 5: " + toString(apply(square, 5)))
    Console.print("Cube of 3: " + toString(apply(cube, 3)))

    // Closures
    let add10 = makeAdder(10)
    Console.print("Add 10 to 5: " + toString(add10(5)))
    Console.print("Add 10 to 20: " + toString(add10(20)))

    // Function composition
    let squareThenCube = compose(cube, square)
    Console.print("Composed: " + toString(squareThenCube(5)))
}

let output = run main() with {}