That is super sweet. It does boil down to essentially a one-liner.

#!/usr/bin/perl

use strict;
use warnings;
use Set::IntSpan;

my @list = (1, 2, 3, 6, 9, 10, 13, 22, 20, 19, 15, 21);

my $rl = Set::IntSpan->new( \@list )->run_list();
print "$rl\n";
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