Why do you need an integer - for real random this must be larger than 64 bits and then you have problems to to find a suitable type for a variable.

What I would like to be able to do would be:

string createPassword(int length) {
     string alphabet = "abcdefg..ABCDEFG..123-_<>l...";
     integer_list randomnumbers = context.get_random_numbers(length, 0, strlen(alphabet));
     string password;
     for (int i : randomnumbers) {
         password.append(alphabet[i]);
     }
     return password;
};

without having to get correct the cornercases of chopping bits into whole numbers and scaling them down in a sane and secure way.