Functional

Source: examples/functional.ion in the repo.

// Functional programming patterns

// Higher-order functions
fn compose(f, g) {
    |x| f(g(x))
}

let double = |x| x * 2;
let inc = |x| x + 1;
let double_then_inc = compose(inc, double);
io::println(f"double_then_inc(5) = {double_then_inc(5)}");  // 11

// Currying
fn add(a) {
    |b| a + b
}
let add10 = add(10);
io::println(f"add10(5) = {add10(5)}");  // 15

// Method chaining pipeline
let result = [1, 2, 3, 4, 5]
    .map(|x| x * x)
    .filter(|x| x > 5)
    .fold(0, |a, b| a + b);
io::println(f"Sum of squares > 5: {result}");  // 9 + 16 + 25 = 50

// flat_map
let nested = [[1, 2], [3, 4], [5]];
let flat = nested.flat_map(|xs| xs.map(|x| x * 10));
io::println(f"flat_map result: {flat}");  // [10, 20, 30, 40, 50]

// reduce (no initial value needed)
let product = [1, 2, 3, 4, 5].reduce(|a, b| a * b);
io::println(f"Product: {product}");  // 120

// zip
let names = ["Alice", "Bob", "Charlie"];
let scores = [95, 82, 73];
let paired = names.zip(scores);
io::println(f"Zipped: {paired}");  // [(Alice, 95), (Bob, 82), (Charlie, 73)]

// chunk
let data = [1, 2, 3, 4, 5, 6, 7];
io::println(f"Chunks of 3: {data.chunk(3)}");  // [[1, 2, 3], [4, 5, 6], [7]]

// sort_by
let words = ["banana", "apple", "cherry"];
let sorted = words.sort_by(|a, b| a.len() - b.len());
io::println(f"By length: {sorted}");  // [apple, banana, cherry]

// Comprehensions
let evens = [x * 2 for x in 0..10];
io::println(f"Evens: {evens}");

let doubled = [(x, x * 2) for x in 0..4 if x > 0];
io::println(f"Doubled: {doubled}");

// Dict comprehension
let squares = #{str(n): n * n for n in 1..=5};
io::println(f"Squares: {squares}");

// Pipeline operator |>
// |> passes as first argument: x |> f(y) = f(x, y)
let words = "hello world";
let result = words.split(" ")
    .map(|w| w.to_upper())
    .join(" -> ");
io::println(f"Pipeline: {result}");  // HELLO -> WORLD

// any/all
let nums = [2, 4, 6, 8];
io::println(f"All even? {nums.all(|x| x % 2 == 0)}");  // true
io::println(f"Any > 5? {nums.any(|x| x > 5)}");  // true