$ perl -Mstrict -Mwarnings -E '
    sub cycle {
        state $i = -1;
        $_[0]->[++$i, $i %= @{$_[0]}];
    }                                                   
    my $stuff = ["a" .. "d"];                               
    print cycle($stuff) for 1..30;
'
abcdabcdabcdabcdabcdabcdabcdab