2.73.b data-directed derivative system

2.73.b.rkt

;#lang planet neil/sicp 
#lang racket
(require (planet soegaard/sicp:2:1/sicp))
(define wave einstein)

(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))

;; sum
(define (install-sum-derivative-package)
  ;; internal procedures
  (define (addend operands) (car operands))
  (define (augend operands) (cdr operands))
  (define (make-sum a b) (list '+ a b))
  (define (deriv-sum operands var)
    (make-sum (deriv (addend operands) var)
              (deriv (augend operands) var)))
  ;; interface to the rest of the system
  (put 'deriv '+ deriv-sum)
  'done)

;; product
(define (install-product-derivative-package)
  (install-sum-derivative-package)
  ;; internal procedure
  (define (multiplier operands) (car operands))
  (define (multiplicand operands) (cdr operands))
  (define (make-product a b) (list '* a b))
  (define (deriv-product operands var)
    (make-sum (make-product (deriv (multiplier operands) var)
                            (multiplicand operands))
              (make-product (multiplier operands)
                            (deriv (multiplicand operands) var))))
  ;; interface to the rest of the system
  (put 'deriv '* deriv-product)
  'done)