#! /usr/bin/perl
use warnings;
use strict;

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

my @ranges = ($input[0]);
for my $i (1 .. $#input) {
    warn "\t@ranges";
    if ($input[ $i - 1 ] + 1 == $input[$i]) {
        $ranges[-1] = (split /:/, $ranges[-1])[0] . ":$input[$i]";
    } else {
        push @ranges, $input[$i];
    }
}

use Test::More tests => 1;
is_deeply \@ranges, [ '1:3', '5:6', '8', '10' ];
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And, for the sake of TIMTOWTDI:

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 .. $#input + 1;
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($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
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