將「Simply Scheme」語言添加到DrRacket

Question

我想完成本書的工作：http://www.eecs.berkeley.edu/~bh/ss-toc2.html。但是我很難得到「Simply Scheme」語言的工作。代碼不會運行。

#lang planet dyoo/simply-scheme:2 
    (parse ’(4 + 3 * 7 - 5/(3 + 4) + 6)) 

我不斷收到以下錯誤消息：「parse：unbound identifier in module in：parse」。

Answer 1

看看這個page，它有完整的說明。只要做到這一點：

#lang racket 
(require (planet dyoo/simply-scheme:2:2)) 

另外要注意的是，’字符是不正確，對引用使用'，這可能是因爲你複製粘貼代碼錯誤排版。

當然，在完成上述操作之後，您必須定義第18章中介紹的過程，它們沒有在您剛剛導入的包中定義！這將肯定工作：

(define (parse expr) 
    (parse-helper expr '() '())) 

(define (parse-helper expr operators operands) 
    (cond ((null? expr) 
    (if (null? operators) 
     (car operands) 
     (handle-op '() operators operands))) 
    ((number? (car expr)) 
    (parse-helper (cdr expr) 
       operators 
       (cons (make-node (car expr) '()) operands))) 
    ((list? (car expr)) 
    (parse-helper (cdr expr) 
       operators 
       (cons (parse (car expr)) operands))) 
    (else (if (or (null? operators) 
       (> (precedence (car expr)) 
      (precedence (car operators)))) 
      (parse-helper (cdr expr) 
       (cons (car expr) operators) 
       operands) 
      (handle-op expr operators operands))))) 

(define (handle-op expr operators operands) 
    (parse-helper expr 
     (cdr operators) 
     (cons (make-node (car operators) 
       (list (cadr operands) (car operands))) 
       (cddr operands)))) 

(define (precedence oper) 
    (if (member? oper '(+ -)) 1 2)) 

(define (compute tree) 
    (if (number? (datum tree)) 
     (datum tree) 
     ((function-named-by (datum tree)) 
     (compute (car (children tree))) 
     (compute (cadr (children tree)))))) 

(define (function-named-by oper) 
    (cond ((equal? oper '+) +) 
    ((equal? oper '-) -) 
    ((equal? oper '*) *) 
    ((equal? oper '/) /) 
    (else (error "no such operator as" oper)))) 

(parse '(4 + 3 * 7 - 5/(3 + 4) + 6)) 
=> '(+ (- (+ (4) (* (3) (7))) (/ (5) (+ (3) (4)))) (6)) 

(compute (parse '(4 + 3 * 7 - 5/(3 + 4) + 6))) 
=> 30 2/7 

Answer 2

我只好回覆，以獲得這兩個簡單的計劃和SICP​​合作，DrRacket 5.4.1。