SICP读书笔记2.4

练习2.73

  1. 因为这两种类型直接表示为scheme的数字和符号，没必要再次抽象成另一种类型。

2.

(define (install-sum-package)
  (put 'deriv '+
       (lambda (exp var)
         (make-sum (deriv (addend exp) var)
                   (deriv (augend exp) var)))))

(define (install-product-package)
  (put 'deriv '*
       (lambda (exp var)
         (make-sum
          (make-product (multiplier exp)
                        (deriv (multiplicand exp) var))
          (make-product (deriv (multiplier exp) var)
                        (multiplicand exp))))))

(define (install-exponentiation-package)
  (put 'deriv '**
       (lambda (exp var)
         (let ((n (exponent exp))
               (u (base exp)))
           (make-product
            n
            (make-product
             (make-exponentiation
              u
              (- n 1))
             (deriv u var)))))))
  1. 把put时候的参数顺序对调一下就可以，比如原本的(put ‘deriv ‘) 改为(put ‘ ‘deriv)