在sicp解释器中将过程定义解释为变量定义吗？

Question

我正在阅读sicp 4.1.4。运行解释器，然后在解释器中输入append函数后，它说确定。但是，当我以4.1.4为例调用append时，它将返回“ Unbound variable append”。我以为我的解释器将其作为变量定义而不是过程定义。但是我不知道为什么。

我已经多次将我的代码检查为示例代码，但仍然无法弄清楚。我在下面发布了我的代码，确实是一个很长的文件。 您能帮我找出问题所在吗？谢谢。

#lang sicp

;;
(define (list-of-values exps env)
  (if (no-operands? exps)
      '()
      (cons (eval (first-operand exps) env)
            (list-of-values (rest-operands exps) env))))
;;
(define (eval-if exp env)
  (if (true? (eval (if-predicate exp) env))
      (eval (if-consequent exp) env)
      (eval (if-alternative exp) env)))
;;
(define (eval-sequence exps env)
  (cond ((last-exp? exps) (eval (first-exp exps) env))
        (else (eval (first-exp exps) env)
              (eval-sequence (rest-exps exps) env))))

;;
(define (eval-assignment exp env)
  (set-variable-value! (assignment-variable exp)
                       (eval (assignment-value exp) env)
                       env))
;;
(define (eval-definition exp env)
  (define-variable! (definition-variable exp)
    (eval (definition-value exp) env)
    env)
  'ok)

;;
(define (self-evaluation? exp)
  (cond ((number? exp) true)
        ((string? exp) true)
        (else false)))
;;
(define (variable? exp)
  (symbol? exp))
;;
(define (quoted? exp)
  (tagged-list? exp 'quote))
(define (text-of-quotation exp)
  (cadr exp))
;;
(define (tagged-list? exp tag)
  (if (pair? exp)
      (eq? (car exp) tag)
      false))
;;
(define (assignment? exp)
  (tagged-list? exp 'set!))
(define (assignment-variable exp)
  (cadr exp))
(define (assignment-value exp)
  (caddr exp))
;;
(define (definition? exp)
  (tagged-list? exp 'define))
(define (definition-variable exp)
  (if (symbol? (cadr exp))
      (cadr exp)
      (caddr exp)))
(define (definition-value exp)
  (if (symbol? (cadr exp))
      (caddr exp)
      (make-lambda (cdadr exp)
                   (cddr exp))))
;;
(define (lambda? exp)
  (tagged-list? exp 'lambda))
(define (lambda-parameters exp)
  (cadr exp))
(define (lambda-body exp)
  (cddr exp))
(define (make-lambda parameters body)
  (cons 'lambda (cons parameters body)))
;;
(define (if? exp)
  (tagged-list? exp 'if))
(define (if-predicate exp)
  (cadr exp))
(define (if-consequent exp)
  (caddr exp))
(define (if-alternative exp)
  (if (not (null? (cdddr exp)))
      (cadddr exp)
      'false))
(define (make-if predicate
                 consequent
                 alternative)
  (list 'if
        predicate
        consequent
        alternative))
;;
(define (begin? exp)
  (tagged-list? exp 'begin))
(define (begin-actions exp)
  (cdr exp))
(define (last-exp? seq)
  (null? (cdr seq)))
(define (first-exp seq) (car seq))
(define (rest-exps seq) (cdr seq))
(define (sequence->exp seq)
  (cond ((null? seq) seq)
        ((last-exp? seq) (first-exp seq))
        (else (make-begin seq))))
(define (make-begin seq) (cons 'begin seq))

;;
(define (application? exp)
  (pair? exp))
(define (operator exp) (car exp))
(define (operands exp) (cdr exp))
(define (no-operands? ops) (null? ops))
(define (first-operand ops) (car ops))
(define (rest-operands ops) (cdr ops))

;;
(define (cond? exp)
  (tagged-list? exp 'cond))
(define (cond-clauses exp) (cdr exp))
(define (cond-else-clause? clause)
  (eq? (cond-predicate clause) 'else))
(define (cond-predicate clause) (car clause))
(define (cond-actions clause) (cdr clause))
(define (cond->if exp)
  (expand-clauses (cond-clauses exp)))
(define (expand-clauses clauses)
  (if (null? clauses)
      'false
      (let ((first (car clauses))
            (rest (cdr clauses)))
        (if (cond-else-clause? first)
            (if (null? rest)
                (sequence->exp (cond-actions first))
                (error "ELSE clause isn't last -- COND->IF" clauses))
            (make-if (cond-predicate first)
                     (sequence->exp (cond-actions first))
                     (expand-clauses rest))))))

(define (true? x) (not (eq? x false)))
(define (false? x) (eq? x false))

(define (make-procedure parameters body env)
  (list 'procedure parameters body env))
(define (compound-procedure? p)
  (tagged-list? p 'procedure))
(define (procedure-parameters p) (cadr p))
(define (procedure-body p) (caddr p))
(define (procedure-environment p) (cadddr p))



; 
(define (enclosing-environment env) (cdr env))
(define (first-frame env) (car env))
(define the-empty-environment '())

(define (make-frame variables values) 
  (cons variables values))
(define (frame-variables frame) (car frame))
(define (frame-values frame) (cdr frame))
(define (add-binding-to-frame! var val frame)
  (set-car! frame (cons var (car frame)))
  (set-cdr! frame (cons val (cdr frame))))

(define (extend-environment vars vals base-env)
  (if (= (length vars) (length vals))
      (cons (make-frame vars vals) base-env)
      (if (< (length vars) (length vals))
        (error "Too many arguments supplied" vars vals)
        (error "Too few arguments supplied" vars vals))))

; 有些重复代码，习题里要求抽象。这里就不写了。
(define (lookup-variable-value var env)
  (define (env-loop env)
    (define (scan vars vals)
      (cond ((null? vars)
              (env-loop (enclosing-environment env)))
            ((eq? var (car vars))
              (car vals))
            (else (scan (cdr vars) (cdr vals)))))
    (if (eq? env the-empty-environment)
      (error "Unbound variable" var)
      (let ((frame (first-frame env)))
        (scan (frame-variables frame)
              (frame-values frame)))))
  (env-loop env))

(define (set-variable-value! var val env)
  (define (env-loop env)
    (define (scan vars vals)
      (cond ((null? vars)
              (env-loop (enclosing-environment env)))
            ((eq? var (car vars))
              (set-car! vals val))
            (else (scan (cdr vars) (cdr vals)))))
    (if (eq? env the-empty-environment)
        (error "Unbound variable -- SET!" var)
        (let ((frame (first-frame env)))
          (scan (frame-variables frame)
                (frame-values frame)))))
  (env-loop env))

(define (define-variable! var val env)
  (let ((frame (first-frame env)))
    (define (scan vars vals)
      (cond ((null? vars)
              (add-binding-to-frame! var val frame))
            ((eq? var (car vars))
              (set-car! vals val))
            (else (scan (cdr vars) (cdr vals)))))
    (scan (frame-variables frame)
          (frame-values frame))))

(define (primitive-procedure? proc)
  (tagged-list? proc 'primitive))
(define (primitive-implementation proc) (cadr proc))  

(define primitive-procedures
  (list (list 'car car)
        (list 'cdr cdr)
        (list 'cons cons)
        (list 'null? null?)
        (list '+ +)))

(define (primitive-procedure-names)
  (map car primitive-procedures))   

(define (primitive-procedure-objects)
  (map (lambda (proc) (list 'primitive (cadr proc)))
        primitive-procedures))

(define (apply-primitive-procedure proc args)
  (apply-in-underlying-scheme
    (primitive-implementation proc) args))
(define apply-in-underlying-scheme apply)   

(define input-prompt ";;; M_Eval input:")
(define output-prompt ";;; M-Eval value:")
(define (driver-loop)
  (prompt-for-input input-prompt)
    (let ((input (read)))
      (let ((output (eval input the-global-environment)))
        (announce-output output-prompt)
        (user-print output)))
  (driver-loop))
(define (prompt-for-input string)
  (newline) (newline) (display string) (newline))
(define (announce-output string)
  (newline) (display string) (newline))  

(define (user-print object)
  (if (compound-procedure? object)
    (display (list 'compound-procedure
                    (procedure-parameters object)
                    (procedure-body object)
                    '<procedure-env>))
    (display object)))  

; 
(define (setup-environment)
  (let ((initial-env
          (extend-environment (primitive-procedure-names)
                              (primitive-procedure-objects)
                              the-empty-environment)))
    (define-variable! 'true true initial-env)
    (define-variable! 'false false initial-env)
    initial-env))

; apply
(define (metacircular-apply procedure arguments)
  (cond ((primitive-procedure? procedure)
         (apply-primitive-procedure procedure arguments))
        ((compound-procedure? procedure)
         (eval-sequence
          (procedure-body procedure)
          (extend-environment (procedure-parameters procedure)
                              arguments
                              (procedure-environment procedure))))
        (else (error "Unknown procedure type -- APPLY" procedure))))

;; eval
(define (eval exp env)
  (cond ((self-evaluation? exp) exp)
        ((variable? exp) (lookup-variable-value exp env))
        ((quoted? exp) (text-of-quotation exp))
        ((assignment? exp) (eval-assignment exp env))
        ((definition? exp) (eval-definition exp env))
        ((if? exp) (eval-if exp env))
        ((lambda? exp)
         (make-procedure (lambda-parameters exp)
                         (lambda-body exp)
                         env))
        ((begin? exp)
         (eval-sequence (begin-actions exp) env))
        ((cond? exp) (eval (cond->if exp) env))
        ((application? exp)
         (metacircular-apply (eval (operator exp) env)
                (list-of-values (operands exp) env)))
        (else (error "Unknown expression type -- EVAL" exp))))

(define the-global-environment (setup-environment)) 
(driver-loop)

Answer 1

我认为问题在于定义变量。备用项应为caadr而不是caddr。即应该是：

(define (definition-variable exp)
  (if (symbol? (cadr exp))
      (cadr exp)
      (caadr exp)))
         ^

更改之后，它似乎可以工作。