class Test1 {
    __str__() {
        fun nested() {
            fun inner() {
                return "Apple";
            }
            return inner();
        }
        return nested();
    }
}

class Test2 {}

var inst1 = Test1();
var inst2 = Test2();

print(str(inst1)); # expect: Apple
print(str(inst2)); # expect: <Test2 instance>