10_closures.mno

# Lesson 10 — First-class functions and closures
# Lambdas capture by value; captured vars are read-only (mutate via struct/array).

fn map_ints(xs: [int], f: fn(int) -> int) -> [int] {
    let out: [int] = []
    for i in 0..len(xs) {
        out = push(out, f(xs[i]))
    }
    return out
}

fn make_adder(n: int) -> fn(int) -> int {
    return fn(x: int) -> int {
        return x + n
    }
}

fn main() {
    let xs = [1, 2, 3]
    let doubled = map_ints(xs, fn(x: int) -> int {
        return x * 2
    })
    print(doubled[0])
    print(doubled[2])
    let add10 = make_adder(10)
    print(add10(5))
}

test "closures" {
    let add3 = make_adder(3)
    assert add3(4) == 7
    let xs = [1, 2]
    let ys = map_ints(xs, fn(x: int) -> int {
        return x + 1
    })
    assert ys[0] == 2
    assert ys[1] == 3
}