sub split_sort {
  my ($in_a, $in_b, $split, $sort_type) = @_;
  $split = qr($split);

  my ($numa1, $numa2) = split(/$split/, $in_a);
  my ($numb1, $numb2) = split(/$split/, $in_b);

  if ($sort_type =~ /^num/) {
    $numa1 <=> $numb1 || $numa2 <=> $numb2
  }
  elsif ($sort_type =~ /^(alpha|letter)/) {
    $numa1 cmp $numb1 || $numa2 cmp $numb2
  }
}