sub flatten { # Depth-first traversal.
  my @scalar;
  foreach my $item (@_) {
    if (ref $item eq 'ARRAY') {
      push @scalar, flatten(@$item);
    } elsif (ref $item eq 'HASH') {
      push @scalar, $_, flatten($$item{$_}) for keys %$item;
    } elsif (ref $item) {
      push @scalar, ref $item;
    } else {
      push @scalar, $item;
    }
  }
  return @scalar;
}

print join ', ', flatten $VAR2;
print "\n";