my @foo = (
    [0, 1, 2, 3, 4, 5],
    [0, 1, 2],
    [0, [ 0, 1, 2, 3 ]]
);

my @maxlength = ();
figger_out_depth(0, @foo);

print "max dimensions:\n";
print "  $_: $maxlength[$_]\n" foreach (0..$#maxlength);

sub figger_out_depth {
    my $depth = shift;
    $maxlength[$depth] = 0 unless(defined($maxlength[$depth]));
    foreach my $element (@_) {
        figger_out_depth($depth + 1, @{$element}) if(ref($element) eq 'ARRAY');
    }
    $maxlength[$depth] = $#_ + 1 if($#_ >= '0'.$maxlength[$depth]);
}