my @input = (1, 2, 3, 5, 6, 8, 10);

my $last = $input[0];
my @ranges = map {
    ($_ > $#input || $input[$_]  != 1 + $input[ $_ - 1 ])
        ? do {
            my $s = $last . (":$input[ $_ - 1 ]") x ($last != $input[ $_ - 1 ]);
            $last = $input[$_];
            $s
        }
        : ();
} 1 .. $#input + 1;