sub traverse_tree {
	my ( $tree_root, $visitor_callback ) = @_;
	my ( $curr_node, $prev_node ) = $tree_root;

	while( $curr_node ) {
		my $next_node;

		if( $prev_node == $curr_node->parent ) {
			$next_node = $curr_node->left;
			if( not $next_node ) {
				$visitor_callback->( $curr_node );
				$next_node = $curr_node->right || $curr_node->parent;
			}
		}
		elsif( $prev_node == $curr_node->left ) {
			$visitor_callback->( $curr_node );
			$next_node = $curr_node->right || $curr_node->parent;
		}
		elsif( $prev_node == $curr_node->right ) {
			$next_node = $curr_node->parent;
		}

		( $prev_node, $curr_node ) = ( $curr_node, $next_node );
	}
}

##</code><code>##

sub traverse_tree {
	my ( $tree_root, $visitor_callback ) = @_;
	my ( $curr_node, $prev_node ) = $tree_root;

	while( $curr_node ) {
		my $next_node;

		{
			goto FROM_PARENT if $prev_node == $curr_node->parent;
			goto FROM_LEFT   if $prev_node == $curr_node->left;
			goto FROM_RIGHT  if $prev_node == $curr_node->right;

			FROM_PARENT:
				last if $next_node = $curr_node->left;

			FROM_LEFT:
				$visitor_callback->( $curr_node );
				last if $next_node = $curr_node->right;

			FROM_RIGHT:
				$next_node = $curr_node->parent;
		}

		( $prev_node, $curr_node ) = ( $curr_node, $next_node );
	}
}