(defun graph-test (stream &optional (orientation :horizontal))
   (fresh-line stream)
   (macrolet ((make-node (&key name children)
                `(list* ,name ,children)))
     (flet ((node-name (node)
              (car node))
            (node-children (node)
              (cdr node)))
       (let* ((2a (make-node :name "2A"))
              (2b (make-node :name "2B"))
              (2c (make-node :name "2C"))
              (1a (make-node :name "1A" :children (list 2a 2b)))
              (1b (make-node :name "1B" :children (list 2b 2c)))
              (root (make-node :name "0" :children (list 1a 1b))))
         (format-graph-from-roots
           (list root)
           #'(lambda (node s)
               (write-string (node-name node) s))
           #'node-children
           :orientation orientation
           :stream stream)))))