연습문제 4.3

(define eval-table (make-table))
(define get (eval-table 'lookup-proc))
(define put (eval-table 'insert-proc!))

(define (eval-quoted exp env)
  (text-of-quotation exp))

(define (eval-set exp env)
  (eval-assignment exp env))
(define (eval-define exp env)
  (eval-definition exp env))
(define (eval-if. exp env)
  (eval-if exp env))
(define (eval-lambda exp env)
  (make-procedure (lambda-parameters exp)
                  (lambda-body exp)
                  env))
(define (eval-begin exp env)
  (eval-sequence (begin-actions exp) env))
(define (eval-cond exp env)
 (eval (cond->if exp) env))
(put 'quote eval-quoted)
(put 'set eval-set)
(put 'define eval-definition)
(put 'if eval-if.)
(put 'lambda eval-lambda)
(put 'begin eval-begin)
(put 'cond eval-cond)


(define (eval exp env)
  (cond ((self-evaluating? exp) exp)
        ((variable? exp) (lookup-variable-value exp env))
        ((get (car exp))
         ((get (car exp)) exp env))
        ((application? exp)
         (apply (eval (operator exp) env)
                (list-of-values (operands exp) evn)))
        (else
         (error "Unknown expression type -- EVAL" exp))))