Simple Maths helper program with between 1 and 3 inputs

simpleMathsHelper.ceylon

String askUser(String question) {
    process.write(question);
    return process.readLine();
}

Float? askUserForNumber(String question) => parseFloat(askUser(question));

void printResult(Float(Float, Float=, Float=) operation, Float x, Float? y, Float? z) {
    Float result;
    if (exists y) {
        if (exists z) {
            result = operation(x, y, z);
        } else {
            result = operation(x, y);
        }
    } else {
        result = operation(x);
    }
    print("Result: ``result``");
}


shared void run() {
    function multiply(Float a, Float b = 1.0, Float c = 1.0) => a * b * c;
    function add(Float a, Float b = 0.0, Float c = 0.0) => a + b + c;
    
    function askForOptionalNumber(String question, Boolean askUser) {
        if (askUser) {
            return askUserForNumber(question);
        } else {
            return null;
        }       
    }
    
    value multiplication = 0;
    value addition = 1;
    value option = askUserForNumber("Enter ``multiplication`` for multiplication, ``addition`` for addition: ");
    value x = askUserForNumber("Enter x: ");
    value y = askForOptionalNumber("Enter y (optional): ", x exists);
    Float? z = askForOptionalNumber("Enter z (optional): ", y exists);
    
    assert(is Float option, is Float x,
            option == multiplication || option == addition);
    
    printResult(option == multiplication then multiply else add, x, y, z);
}