【SICP练习】84 练习2.56

来源：互联网发布：大金焓湿图计算软件编辑：程序博客网时间：2024/04/29 10:51

这道题的代码略长啊。不过我也是因此而知道Edwin上的代码居然可以复制到word上，以前还想当然的以为不能复制的，毕竟在Edwin上粘贴用的Ctrl+Y，而不是Ctrl+V。在这里我就只将书上没有的代码贴出来了。

(define (deriv exp var)   (cond ((number? exp) 0)         ((variable? exp)          (if (same-variable? exp var) 1 0))         ((sum? exp)          (make-sum (deriv (addend exp) var)                     (deriv (augend exp) var)))((product? exp)           (make-sum (make-product (multiplier exp)                                     (deriv (multiplicand exp) var))                       (make-product (deriv (multiplier exp) var)                                     (multiiplicand exp))))           ((exponentiation? exp)     (let ((n (exponent exp))                  (u (base exp)))              (make-product                    n                   (make-product                         (make-exponentiation                             u                             (- u 1))                       (deriv u var)))))    (else             (error "unknown expression type -- DERIV" exp))))(define (make-exponentiation base exponent)  (cond ((= exponent 0)     1)    ((= exponent 1)     base)    (else      (list '** base exponent))))(define (exponentiation? x)  (and (pair? x)       (eq? (car x) '**)))(define (base exp)  (cadr exp))(define (exponent exp)  (caddr exp))

5 0