my $comb = comb([qw(a b c)],[qw(1 2 3)],[qw(- + *)]);

require Data::Dumper;
print(Data::Dumper::Dumper(
   comb([qw(a b c)],[qw(1 2 3)],[qw(- + *)])
));

print(scalar(@$comb), "\n");  # 27