# snufkon/SICP

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 (define (variable? x) (symbol? x)) (define (same-variable? v1 v2) (and (variable? v1) (variable? v2) (eq? v1 v2))) (define (=number? exp num) (and (number? exp) (= exp num))) (define (augend s) (caddr s)) (define (multiplicand p) (caddr p)) (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) (multiplicand exp)))) (else (error "unknown expression type -- DERIV" exp)))) ;;; a. 中置記法の代数式を微分するように改良 (define (sum? x) (and (pair? x) (eq? (cadr x) '+))) (define (product? x) (and (pair? x) (eq? (cadr x) '*))) (define (addend s) (car s)) (define (multiplier p) (car p)) (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 (make-product m1 m2) (cond ((or (=number? m1 0) (=number? m2 0)) 0) ((=number? m1 1) m2) ((=number? m2 1) m1) ((and (number? m1) (number? m2)) (* m1 m2)) (else (list m1 '* m2)))) ;;; 使用例 (deriv '(x + 3) 'x) ; 1 (deriv '(x + (3 * (x + (y + 2)))) 'x) ; 4