Ok, well, I spent way too much time on this and came up with a really convoluted solution. But it has two nice features: a) an OO module, and b) ability to add more values later. Here goes. 
package Subsequence;
use overload '""' => \&list_form;

sub new {
  my $package = shift || __PACKAGE__;
  return bless {ranges => {}, vals => {}}, $package;
}

sub insert_list {
  my $self = shift;
  my $vals = $self->{vals};
  foreach my $val (sort { $a <=> $b } @_) {
    next if exists $vals->{$val};
    if (exists $vals->{$val - 1}) {
      $vals->{$val} = $vals->{$val - 1};
      $vals->{$val}->{end} = $val;
      if (exists $vals->{$val + 1}) {
        $vals->{$val}->{end} = $vals->{val + 1}->{end};
        my $item = $vals->{val + 1};
        for my $i ($val + 1 .. $vals->{$val}->{end}) {
           $vals->{$i} = $vals-{$val};
        }
        delete $self->{ranges}->{$item};
      }
    } elsif (exists $vals->{$val + 1}) {
      $vals->{$val} = $vals->{$val + 1};
      $vals->{$val}->{start} = $val;
    } else {
      my $item = { start => $val, $end => $val };
      $vals->{$val} = $item;
      $self->{ranges}->{$item} = $item;
    }
  }
  return $self;
}

sub list_form {
  my $self = shift;
  my $ranges = $self->{ranges};
  return "(" . ( join ", ", map { $_->{start} == $_->{end} ?
                  $_->{start} :
                    "$_->{start}..$_->{end}" }
                     sort {$a->{start} <=> $b->{start} }
                     values %$ranges  )
    . ")";
}
1;

[download]
and used as 
use Subsequence;
my @test_nums = (0, 10, 11, 12, 2, 4, 3, 5, 6, 7, 9);
my $x = Subsequence->new->insert_list(@test_nums);
print $x, "\n";
$x->insert_list(1, 13);
print $x, "\n";

[download]
This is ugly I know, but the first solution I wrote up using only arrays was even uglier, though it had the advantage of not sorting every time on retrieval. But I just couldn't figure out how to make it work generically, which was really frustrating.

In reply to Re: Display array as ranges? by Errto
in thread Display array as ranges? by xipho

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