generator<int> primes(int start, int end){
    for ( int i = start; i < end; i++ ){
        if ( is_prime(i) ){
            yield i;
        }
    }
}

for ( auto prime : primes(100, 10000) ){
    cout << prime << " ";
}


struct unnamed_generator{
    int state;
    int local_i;
    int start;
    int end;

    unnamed_generator(int start, int end)
        : start(start)
        , end(end){
    }

    std::optional<int> resume(){
        switch ( state ){
        case 0:{
            local_i = start;
            state = 1;
            return resume();
        }break;
        case 1:{
            if ( local_i >= end ){
                state = 3;
                return resume();
            }

            if ( is_prime(local_i) ){
                state = 2;
                return local_i;
            }
            state = 2;
            return resume();
        }break;
        case 2:{
            local_i++;
            state = 1;
            return resume();
        }break;
        default:{
            return nullptr;
        }break;
        }
    }
}

unnamed_generator generator(100, 10000);
while ( auto prime = generator.resume().get() ){
    cout << prime;
}