huffman.rkt

(require racket/trace)

(define (make-leaf symbol weight) (list 'leaf symbol weight))
(define (leaf? object) (eq? (car object) 'leaf))
(define (symbol-leaf x) (cadr x))
(define (weight-leaf x) (caddr x))

(define (make-code-tree left right)
	(list left
		  right
		  (append (symbols left) (symbols right))
		  (+ (weight left) (weight right))))
		
(define (left-branch tree) (car tree))
(define (right-branch tree) (cadr tree))
(define (symbols tree)
	(if (leaf? tree)
		(list (symbol-leaf tree))
		(caddr tree)))
(define (weight tree)
	(if (leaf? tree)
    	(weight-leaf tree)
      	(cadddr tree)))

(define sample-tree (make-code-tree (make-leaf 'A 4)
                  (make-code-tree
                   (make-leaf 'B 2)
                   (make-code-tree
                    (make-leaf 'D 1)
					(make-leaf 'C 1)))))

(define sample-message '(0 1 1 0 0 1 0 1 0 1 1 1 0))

(define plaintext-message '(A D A B B C A))