Backend systems and programming languages.

func multiplyBy = define(factor) {
    func multiplier = define(number) {
        return number * factor;
    }
    return multiplier;
}
let double = multiplyBy(2);
let triple = multiplyBy(3);
output(double(5));
output(triple(5));

$ python -m src.Main run closures.flx
10
15

func add = define(a, b) { return a + b; }
func subtract = define(a, b) { return a - b; }
func multiply = define(a, b) { return a * b; }
func divide = define(a, b) { return a / b; }

output("10 + 5 = " + add(10, 5));
output("10 - 5 = " + subtract(10, 5));
output("10 * 5 = " + multiply(10, 5));
output("10 / 5 = " + divide(10, 5));

$ python -m src.Main run functions.flx
10 + 5 = 15
10 - 5 = 5
10 * 5 = 50
10 / 5 = 2

struct Task {
    name;
    done;
}

let tasks = [];
tasks.push(Task("Write parser", true));
tasks.push(Task("Add structs", true));
tasks.push(Task("Ship v0.2.0", false));

foreach (t: tasks) {
    let mark = "[ ]";
    if (t.done) { mark = "[x]"; }
    output(mark + " " + t.name);
}

$ python -m src.Main run structs.flx
[x] Write parser
[x] Add structs
[ ] Ship v0.2.0

func makePrefixer = define(prefix) {
    func addPrefix = define(str) {
        return prefix + str;
    }
    return addPrefix;
}

let logInfo = makePrefixer("[INFO] ");
let logError = makePrefixer("[ERROR] ");

output(logInfo("System initialized"));
output(logError("Connection to remote host failed"));
output(logInfo("Retrying in 3 seconds..."));

$ python -m src.Main run strings.flx
[INFO] System initialized
[ERROR] Connection to remote host failed
[INFO] Retrying in 3 seconds...