use Algorithm::Loops qw( NestedLoops );
my $source = 'horse:cow:dog:cat';
my @parts = split(/:/, $source);
my $iter = NestedLoops(
[
[ 0..$#parts ],
( sub { [ $_+1..$#parts ] } ) x $#parts,
],
{ OnlyWhen => 1 },
);
my @s;
print(join(':', map $parts[$_], @s), "\n")
while @s = $iter->();
####
my $source = 'horse:cow:dog:cat';
my @parts = split(/:/, $source);
for my $comb (1..2**@parts-1) {
my $s = join ':',
map $parts[$_],
grep $comb & (1<<$_),
0..$#parts;
print("$s\n");
}
##
##
my $source = 'horse:cow:dog:cat';
local $_ = ":$source:";
my $parts = tr/:/:/ - 1;
my $re = '(?{ "" })'
. '(:[^:]*)(?=:)(?{ $^R . $^N })'
. '(?:.*(:[^:]*)(?=:)(?{ $^R . $^N })' x ($parts-1)
. ')?' x ($parts-1)
. '(?{ push @rv, substr($^R, 1) })'
. '(?!)';
{ use re 'eval'; $re = qr/$re/; }
local our @rv;
/$re/;
print "$_\n" foreach @rv;