}

    @Override
    public String toString() {
        return input.substring(pos);
    }

    public boolean isEmpty() {
        return pos == input.length();
    }

    public void mark() {
        markPos = pos;
    }

    public void next() {
        next(1);
    }

    public void next(int n) {
        pos += n;
    }

    public boolean lookingAt(char c) {