seed the stack with the first instance
while (stack has entries) 
     pop off top entry from stack
     process it
     take any potential new work as a result of 
          processing, put it back on the stack
[download]

Of course this only replaces the subroutine stack with your own, but it can be quicker and save memory. (Sometimes it's a lot more obvious too!)

From a /msg request for dragonchild, here's pseudocode to do a directory traversal without recursion.

# Traverse the filesystem
push to stack /
while currentdirectory = pop stack
     open the currentdirectory
     foreach pathname in this directory
           if it's also a directory, push it (full path) 
              on the stack
     close the current directory
[download]

As opposed to a recursive solution:

call traverse(/)
function traverse (currentdirectory)
     open currentdirectory
     foreach pathname in this directory
           if it's also a directory, traverse(pathname)
     close currentdirectory
[download]

For those who don't grok pseudocode here's a perl translation for directory traversal without recursion

my @stack = ".";
while(my $cd = pop @stack) {
    opendir(my $dh, $cd) or die("bad dir - $!");
    foreach (readdir($dh)) {
        next if /^\./;
        print $_.$/;
        push @stack, "$cd/$_" if -d "$cd/$_";
    }
}
[download]

and with recursion

&traverse(".");
sub traverse {
    my $dir = shift;
    opendir(my $dh, $dir) or die("bad dir - $!");
    foreach (readdir($dh)) {
        next if /^\./;
        print $_.$/;
        &traverse("$dir/$_") if -d "$dir/$_";
    }
}
[download]

That's a pretty neat 'trick' which I guess might be how optimising compilers implement some forms of recursion (or something).
HTH

broquaint