oooh, fun!

use strict;
use warnings;

my $zero = shift || 3;
my $one  = shift || 2;

my @array = ( (0) x $zero, (1) x $one );
# print "@array\n";
print join ('', @array), "\n";

while (1) {
    my $cand = $#array;
    while ($cand) {
        if ($array[$cand-1] == 0 and $array[$cand] == 1) {
            ($array[$cand-1], $array[$cand]) = ($array[$cand], $array[
+$cand-1]);
            if ($cand < $#array) {
                @array[$cand+1..$#array] = sort @array[$cand+1..$#arra
+y];
            }
            last;
        }
        --$cand;
    }
    last unless $cand;
    # print "@array\n";
    print join ('', @array), "\n";
}
[download]

Converting this to an iterator is left as an exercise to the reader (update:) remarkably trivial :)

sub iter {
    my $zero  = shift || 3;
    my $one   = shift || 2;
    my $init  = 0;
    my @array = ( (0) x $zero, (1) x $one );

    return sub {

        $init++ or return join('', @array);

        my $cand = $#array;
        while ($cand) {
            if ($array[$cand-1] == 0 and $array[$cand] == 1) {
                ($array[$cand-1], $array[$cand]) = ($array[$cand], $ar
+ray[$cand-1]);
                if ($cand < $#array) {
                    @array[$cand+1..$#array] = sort @array[$cand+1..$#
+array];
                }
                last;
            }
            --$cand;
        }
        return $cand ? join( '', @array) : undef;
    }
}

my $i = iter(@ARGV);

while (my $str = $i->()) {
    print "$str\n";
}
[download]

update: tye was right (of course!), the sort may be advantageously replaced by a reverse. Furthermore, there is no point in reversing (or sorting) a one-element array...

    $cand < $#array - 1 and
         @array[$cand+1..$#array] = reverse @array[$cand+1..$#array];
[download]

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