ruandao

;#lang planet neil/sicp 
#lang racket
(require (planet soegaard/sicp:2:1/sicp))
(define wave einstein)

(define (lookup  key bt-data)
  (cond ((empty? bt-data) false)
        ((> key (key-of-root bt-data)) (lookup key (right-branch bt-data)))
        ((= key (key-of-root bt-data)) (entry-of-root bt-data))
        ((< key (key-of-root bt-data)) (lookup key (left-branch bt-data)))))

ruandao

;#lang planet neil/sicp 
#lang racket
(require (planet soegaard/sicp:2:1/sicp))
(define wave einstein)

(define (make-code-tree left right)
  (list left
        right
        (append (symbols left) (symbols right))
        (+ (weight left) (weight right))))

ruandao

;#lang planet neil/sicp 
#lang racket
(require (planet soegaard/sicp:2:1/sicp))
(define wave einstein)


(define (make-leaf symbol weight)
  (list 'leaf symbol weight))

(define (leaf? obj)

ruandao

;#lang planet neil/sicp 
#lang racket
(require (planet soegaard/sicp:2:1/sicp))
(define wave einstein)


(define (make-leaf symbol weight)
  (list 'leaf symbol weight))

(define (leaf? obj)

ruandao

;#lang planet neil/sicp 
#lang racket
(require (planet soegaard/sicp:2:1/sicp))
(define wave einstein)


(define (make-leaf symbol weight)
  (list 'leaf symbol weight))

(define (leaf? obj)

ruandao

;#lang planet neil/sicp 
#lang racket
(require (planet soegaard/sicp:2:1/sicp))
(define wave einstein)


(define (make-leaf symbol weight)
  (list 'leaf symbol weight))

(define (leaf? obj)

ruandao

;#lang planet neil/sicp 
#lang racket
(require (planet soegaard/sicp:2:1/sicp))
(define wave einstein)


(define (make-leaf symbol weight)
  (list 'leaf symbol weight))

(define (leaf? obj)

ruandao

;#lang planet neil/sicp 
#lang racket
(require (planet soegaard/sicp:2:1/sicp))
(define wave einstein)

(define (deriv exp var)
  (cond ((number? exp) 0)
        ((variable? exp) (if (same-variable? exp var) 1 0))
        (else ((get 'deriv (operator exp)) (operands exp) var))))
(define (operator exp) (car exp))

ruandao

;#lang planet neil/sicp 
#lang racket
(require (planet soegaard/sicp:2:1/sicp))
(define wave einstein)

(define (deriv exp var)
  (cond ((number? exp) 0)
        ((variable? exp) (if (same-variable? exp var) 1 0))
        (else ((get 'deriv (operator exp)) (operands exp) var))))
(define (operator exp) (car exp))

ruandao

;#lang planet neil/sicp 
#lang racket
(require (planet soegaard/sicp:2:1/sicp))
(define wave einstein)

;; how division's file should structured
;;a '((name1 . rest-of-record) (name2 . rest-of-record) ...)
(define (get-record name file)
  (define (read-file-as-list file)
    ;; 没有io操作的具体信息, 先这样