use Modern::Perl;

#my $alphabet    = ['a'..'z', 'A'..'Z'];
#my $word_length = 6;
my $alphabet    = ['a'..'b', '_'];
my $word_length = 3;


sub create_dictionary {
    my ($alphabet, $word_length) = @_;

    my @odometer  = (0) x $word_length;
    my $len_alpha = @$alphabet;
    my $exhausted = 0;

    return sub {
        my $str = undef;
        if (!$exhausted) {
            $str       = join('', map { $alphabet->[$_] } @odometer);
            my $add    = 1;
            @odometer  = map { $_+=$add; $add = $_ >= $len_alpha ? 1:0; $_% $len_alpha } @odometer;
            $exhausted = $add; # last carry == 1  => exhausted!
        }
        return $str;
    };
}

my $dict = create_dictionary($alphabet, $word_length);

while (my $word =  $dict->()) {
    say $word;
}