1 (load "common")
2 (defun make-leaf (symbol weight)
3   (list 'leaf sym weight))
4 (defun leaf? (obj)
5   (eq (car obj) 'leaf))
6 (defun symbol-leaf (x)
7   (cadr x))
8 (defun weight-leaf (x)
9   (caddr x))
10 (defun make-code-tree (left right)
11   (list left
12 	right
13 	(append (symbols left) (symbols right))
14 	(+ (weight left) (weight right))))
15 (defun left-branch (tree)
16   (car tree))
17 (defun right-branch (tree)
18   (cadr tree))
19 (defun symbols (tree)
20   (if (leaf? tree)
21       (list (symbol-leaf tree))
22       (caddr tree)))
23 (defun weight (tree)
24   (if (leaf? tree)
25       (weight-leaf tree)
26       (cadddr tree)))
27 (defun adjoin-set (x set)
28   "Add a new element _x_ into a set of elements, sorted by weight"
29   (cond ((null set) (list x))
30 	((< (weight x) (weight (car set)))
31 	 (cons x set))
32 	(t (cons (car set)
33 		 (adjoin-set x (cdr set))))))