gistfile1.pl

#!/usr/bin/env perl
use Modern::Perl;

sub is_prime {
    my $n = shift;

    $n <= 1 and return;

    my $i = 1;

    while (++$i**2 <= $n) {
        return 0 if not $n % $i;
    }

    return 1;
}

sub primes {
    my $i = 1;

    return sub {
        do { ++$i } until ( is_prime($i) );
        return $i;
    }
}

my $prime_stream = primes();
my $prime = $prime_stream->();
my $sum = 0;

while ( $prime < 2_000_000) {
    $sum  += $prime;
    $prime = $prime_stream->();
}

say $sum;