1 (defun make-tree (entry left right)
2   (list entry left right))
3 (defun make-leaf (entry)
4   (list entry nil nil))
5 (defun entry (tree)
6   (car tree))
7 (defun set-entry! (tree ent)
8   (setf (car tree) ent))
9 (defun left-branch (tree)
10   (cadr tree))
11 (defun set-let-branch! (tree lb)
12   (setf (cadr tree) lb))
13 (defun right-branch (tree)
14   (caddr tree))
15 (defun set-right-branch! (tree lb)
16   (setf (caddr tree) lb))
17 
18 (defun make-record (key data)
19   (list key data))
20 (defun key (record)
21   (car record))
22 (defun data (record)
23   (cadr record))
24 (defun make-table (&key (<? #'<))
25   (let ((local-table (cons '*head* nil)))
26     (labels (
27 	     (tree-root ()
28 	       (cdr local-table))
29 	     (set-tree-root! (node)
30 	       (setf (cdr local-table) node))
31 	     (node-lookup (key node)
32 	       (if (null node)
33 		   nil
34 		   (let* ((cur-entry (entry node))
35 			  (cur-key (key cur-entry)))
36 		     (cond ((funcall <? key cur-key)
37 			    (node-lookup
38 			     key
39 			     (left-branch node)))
40 			   ((funcall <? cur-key key)
41 			    (node-lookup
42 			     key
43 			     (right-branch node)))
44 			   (t
45 			    cur-entry))))))