$ perl -MData::Dumper -e '$foo=[1..5]; $bar=[[6..10], $foo];$d=Data::Dumper->new([$bar]); $d->Seen({foo => $foo}); print $d->Dump'
$VAR1 = [
          [
            6,
            7,
            8,
            9,
            10
          ],
          [
            1,
            2,
            3,
            4,
            5
          ]
        ];