{ # WRONG:
  my @queue = ();
  foreach (@_) {
    my ($a, $b, $ch) = /(\d*)[:]([^:])[:](.*?)$/;
    my %parent = (a => $a, b => $b);
    my @children = map
      { my ($d, $e, $f) = split /:/, $_;
        my %c = (d=>$d, e=>$e, f=>$f,
                 p=>\%parent);
        \%c; } split /,/, $ch;
    $parent{children}=\@children;
    push @queue, \%parent;
  }
  while (pop @queue) {
    do_stuff($_);
  }
  # The item that was popped off the queue now is out of scope,
  # but its children point back to it, so it stays in memory.
}
# Now the whole queue is out of scope, but the items formerly
# in it are still in memory, even now -- and there's no way
# to get back to them and free them, because you've lost
# track of all the references, even though they still exist.

{ # BETTER:
  my @queue = ();
  foreach (@_) {
    my ($a, $b, $ch) = /(\d*)[:]([^:])[:](.*?)$/;
    my %parent = (a => $a, b => $b);
    my @children = map
      { my ($d, $e, $f) = split /:/, $_;
        my %c = (d=>$d, e=>$e, f=>$f,
                 p=>\%parent);
        \%c; } split /,/, $ch;
    $parent{children}=\@children;
    push @queue, \%parent;
  }
  while (pop @queue) {
    do_stuff($_);
    foreach (@{$$_{children}}) {
      $$_{p}=undef; # child no longer has reference to parent.
    }
    undef $_;  # Now there are zero references to the item,
               #  so it does go away, taking with it its
               #  ch key and the anon array that is its
               #  value, which drops the refcount to each
               #  element of that array to zero, causing
               #  them to be freed, which in turn frees
               #  each of the children -- I think.
  }
}