// Demonstrating functional programming features

// Higher-order functions
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))

// Basic functions
fn double(x: Int): Int = x * 2
fn addOne(x: Int): Int = x + 1
fn square(x: Int): Int = x * x

// Using apply
let result1 = apply(double, 21)  // 42

// Using compose
let doubleAndAddOne = compose(addOne, double)
let result2 = doubleAndAddOne(5)  // 11

// Using the pipe operator
let result3 = 5 |> double |> addOne |> square  // ((5 * 2) + 1)^2 = 121

// Currying example
fn add(a: Int): fn(Int): Int =
    fn(b: Int): Int => a + b

let add5 = add(5)
let result4 = add5(10)  // 15

// Partial application simulation
fn multiply(a: Int, b: Int): Int = a * b

let times3 = fn(x: Int): Int => multiply(3, x)
let result5 = times3(7)  // 21

// Working with records
let transform = fn(record: { x: Int, y: Int }): Int =>
    record.x + record.y

let point = { x: 10, y: 20 }
let sum = transform(point)  // 30