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

# initial source in sequence order
my $source = 'horse:cow:dog:cat';

function($source);

# and now the results
foreach (function($source)) {
    print "$_\n";
}

# generate array of combinations
sub function {
    my @t = split /:/, shift;
    my @res=(shift @t);
    for my $i (@t) {
        @res=($i, @res, map{$_.':'.$i} @res);
    }
    return @res;
}