2.73.ss

(define (variable? e) (symbol? e))
(define (same-variable? v1 v2) 
  (and (variable? v1) (variable? v2) (eq? v1 v2)))
(define (=number? exp num) (and (variable? exp) (= exp num)))

(define (deriv exp var)
  (cond ((number? exp) 0)
        ((variable? exp) (if (same-variable? exp var) 1 0))
        (else
         ((get 'deriv (operator exp)) (operands exp) var))))

(define (operator exp) (car exp))

(define (operands exp) (cdr exp))

(define (install-sum-package)
  (define (addend e) (car e))
  (define (augend e) (cadr e))
  (define (make-sum a1 a2)
    (cond ((=number? a1 0) a2)
          ((=number? a2 0) a1)
          ((and (number? a1) (number? a2)) (+ a1 a2))
          (else (list '+ a1 a2))))
  (define (deriv exp var)
    (make-sum (deriv (addend exp) var)
              (deriv (augend exp) var)))
  
  (put 'deriv '(+) deriv)
  'done)

(define (install-product-package)
  (define (multiplier p) (car p))
  (define (multiplicand p) (cadr p))
  (define (make-product m1 m2)
    (cond ((or (=number? m1 0) (=number? m2 0)) 0)
          ((and (number? m1) (number? m2)) (* m1 m2))
          ((=number? m1 1) m2)
          ((=number? m2 1) m1)
          (else (list '* m1 m2))))
  (define (make-sum a1 a2)
    (cond ((=number? a1 0) a2)
          ((=number? a2 0) a1)
          ((and (number? a1) (number? a2)) (+ a1 a2))
          (else (list '+ a1 a2))))
  (define (deriv exp var)
    (make-sum
     (make-product (multiplier exp)
                   (deriv (multiplicand exp) var))
     (make-product (deriv (multiplier exp) var)
                   (multiplicand exp))))
  
  (put 'deriv '(*) deriv)
  'done)