try catch if else

case DO:
        do {
            try {
                execute(n.body, x);
            } catch (e if e == BREAK && x.target == n) {
                break;
            } catch (e if e == CONTINUE && x.target == n) {
                continue;
            }
        } while (getValue(execute(n.condition, x)));
        break;

catch部分が面白い。ifで条件分岐できるのか。。。