G'day rje,

Here's a solution using state, which therefore requires 5.10.0 or later:

$ perl -Mstrict -Mwarnings -E '
    sub cycle {
        state %i;
        no warnings "uninitialized";
        $_[0]->[($i{$_[0]} % @{$_[0]}, ++$i{$_[0]})[0]];
    }                                                       
    my $a2d = ["a" .. "d"];
    my $e2h = ["e" .. "h"];
    for (1..3) {
        print cycle($a2d) for 1..3;
        print cycle($e2h) for 1..3;
    }                              
'
abcefgdabhefcdaghe
[download]

For earlier Perls, this uses a closure and retains the same level of privacy for %i:

$ perl -Mstrict -Mwarnings -E '
    {          
        my %i;
        sub cycle {
            no warnings "uninitialized";
            $_[0]->[($i{$_[0]} % @{$_[0]}, ++$i{$_[0]})[0]];
        }                  
    }                      
    my $a2d = ["a" .. "d"];
    my $e2h = ["e" .. "h"];
    for (1..3) {
        print cycle($a2d) for 1..3;
        print cycle($e2h) for 1..3;
    }
'
abcefgdabhefcdaghe
[download]

If you only ever want to cycle through a single array (I wasn't sure if that's what your OP was suggesting), then this would be faster (but has distinct limitations):

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

Obviously, that can also be modified for earlier Perls in the same manner as the previous example.