Okay, sorry! Try this iterator then. It will handle upto 32 0s + 1s.

If you uncomment the second example it runs on a bit.

Update: Had to tweak the termination condition. It works now but I'm not happy with it.

Update2: D'oh! No need to count both 1s and 0s.

#! perl -slw
use strict;

sub combs {
    my( $ones, $zeros ) = @_;
    my $n = $ones+$zeros;
    my $max = 2**$n;
    my $p = 0;
    return sub {
        my $x = '';
        $x = unpack "b$n", pack 'V', $p++
            until $x =~ tr[1][] == $ones
            or $p > $max and return;
        return $x;
    }
}

my $iter = combs( 2, 3 );
print while $_ = $iter->();

#my $iter = combs( 14, 6 );
#print while $_ = $iter->();
__END__
C:\test>junk7
11000
10100
01100
10010
01010
00110
10001
01001
00101
00011
[download]

That's a very nice algorythm, but it's a bit slow, and 2 questions:
1. how can i work with (much)more that 32 1's+0's ?
2. why do i need $max to be 2**$n ? when combs(2,3) gives 10 reasults not 32 ???

i need this sub{} to play with the strings that contain that number of 1's and 0's, not the numbers that contain them.