SICP問題2.80
通常の数、有理数および複素数に対して働く、引数が零かどうかテストする汎用述語 =zero? を定義し、汎用算術演算パッケージに設定する。
; 汎用演算パッケージ (define (add x y) (apply-generic 'add x y)) (define (sub x y) (apply-generic 'sub x y)) (define (mul x y) (apply-generic 'mul x y)) (define (div x y) (apply-generic 'div x y)) (define (equ? x y) (apply-generic 'equ? x y)) ; 追加 (define (=zero? x) (apply-generic '=zero? x)) ; 通常(ordinary) (define (install-scheme-number-package) (define (tag x) (attach-tag 'scheme-number x)) (put 'add '(scheme-number scheme-number) (lambda (x y) (tag (+ x y)))) (put 'sub '(scheme-number scheme-number) (lambda (x y) (tag (- x y)))) (put 'mul '(scheme-number scheme-number) (lambda (x y) (tag (* x y)))) (put 'div '(scheme-number scheme-number) (lambda (x y) (tag (/ x y)))) (put 'equ? '(scheme-number scheme-number) (lambda (x y) (= x y))) ; 追加 (put '=zero? '(scheme-number) (lambda (x) (= x 0))) (put 'make 'scheme-number (lambda (x) (tag x))) 'done) (define (make-scheme-number n) ((get 'make 'scheme-number) n)) ; 有理数算術演算 (define (install-rational-package) ;; 内部手続き (define (numer x) (car x)) (define (denom x) (cdr x)) (define (make-rat n d) (let ((g (gcd n d))) (cons (/ n g) (/ d g)))) (define (add-rat x y) (make-rat (+ (* (numer x) (denom y)) (* (numer y) (denom x))) (* (denom x) (denom y)))) (define (sub-rat x y) (make-rat (- (* (numer x) (denom y)) (* (numer y) (denom x))) (* (denom x) (denom y)))) (define (mul-rat x y) (make-rat (* (numer x) (numer y)) (* (denom x) (denom y)))) (define (div-rat x y) (make-rat (* (numer x) (denom y)) (* (denom x) (numer y)))) (define (equ-rat x y) (= (* (numer x) (denom y)) (* (numer y) (denom x)))) ; 追加 (define (=zero-rat x) (and (= (numer x) 0) (not (= (denom x) 0)))) ;; システムの他の部分へのインタフェース (define (tag x) (attach-tag 'rational x)) (put 'add '(rational rational) (lambda (x y) (tag (add-rat x y)))) (put 'sub '(rational rational) (lambda (x y) (tag (sub-rat x y)))) (put 'mul '(rational rational) (lambda (x y) (tag (mul-rat x y)))) (put 'div '(rational rational) (lambda (x y) (tag (div-rat x y)))) (put 'equ? '(rational rational) (lambda (x y) (equ-rat x y))) ; 追加 (put '=zero? '(rational) (lambda (x) (=zero-rat x))) (put 'make 'rational (lambda (n d) (tag (make-rat n d)))) 'done) (define (make-rational n d) ((get 'make 'rational) n d)) ; 直行座標 (define (install-rectangular-package) ;;内部手続き (define (real-part z) (car z)) (define (imag-part z) (cdr z)) (define (make-from-real-imag x y) (cons x y)) (define (magnitude z) (sqrt (+ (square (real-part z)) (square (imag-part z))))) (define (angle z) (atan (imag-part z) (real-part z))) (define (make-from-mag-ang r a) (cons (* r (cos a)) (* r (sin a)))) ;; システムの他の部分とのインタフェース (define (tag x) (attach-tag 'rectangular x)) (put 'real-part '(rectangular) real-part) (put 'imag-part '(rectangular) imag-part) (put 'magnitude '(rectangular) magnitude) (put 'angle '(rectangular) angle) (put 'make-from-real-imag 'rectangular (lambda (x y) (tag (make-from-real-imag x y)))) (put 'make-from-mag-ang 'rectangular (lambda (r a) (tag (make-from-mag-ang r a)))) 'done) ; 極座標 (define (install-polar-package) ;;内部手続き (define (magnitude z) (car z)) (define (angle z) (cdr z)) (define (make-from-mag-ang r a) (cons r a)) (define (real-part z) (* (magnitude z) (cos (angle z)))) (define (imag-part z) (* (magnitude z) (sin (angle z)))) (define (make-from-real-imag x y) (cons (sqrt (+ (square x) (square y))) (atan y x))) ;; システムの他の部分とのインタフェース (define (tag x) (attach-tag 'polar x)) (put 'real-part '(polar) real-part) (put 'imag-part '(polar) imag-part) (put 'magnitude '(polar) magnitude) (put 'angle '(polar) angle) (put 'make-from-real-imag 'polar (lambda (x y) (tag (make-from-real-imag x y)))) (put 'make-from-mag-ang 'polar (lambda (r a) (tag (make-from-mag-ang r a)))) 'done) ; apply-generic を使った汎用選択子の定義 (define (real-part z) (apply-generic 'real-part z)) (define (imag-part z) (apply-generic 'imag-part z)) (define (magnitude z) (apply-generic 'magnitude z)) (define (angle z) (apply-generic 'angle z)) ; パッケージの外部のプログラムから、それぞれの構成子を使用する (define (make-from-real-imag x y) ((get 'make-from-real-imag 'rectangular) x y)) (define (make-from-mag-ang r a) ((get 'make-from-mag-ang 'polar) r a)) ; 複素数 (define (install-complex-package) ;; 直交座標と極座標パッケージから取り入れた手続き (define (make-from-real-imag x y) ((get 'make-from-real-imag 'rectangular) x y)) (define (make-from-mag-ang r a) ((get 'make-from-mag-ang 'polar) r a)) ;; 内部手続き (define (add-complex z1 z2) (make-from-real-imag (+ (real-part z1) (real-part z2)) (+ (imag-part z1) (imag-part z2)))) (define (sub-complex z1 z2) (make-from-real-imag (- (real-part z1) (real-part z2)) (- (imag-part z1) (imag-part z2)))) (define (mul-complex z1 z2) (make-from-real-imag (* (magnitude z1) (magnitude z2)) (* (angle z1) (angle z2)))) (define (div-complex z1 z2) (make-from-real-imag (/ (magnitude z1) (magnitude z2)) (- (angle z1) (angle z2)))) (define (equ-complex z1 z2) (and (= (real-part z1) (real-part z2)) (= (imag-part z1) (imag-part z2)))) ; 追加 (define (=zero-complex z) (and (= (real-part z) 0) (= (imag-part z) 0))) ;; システムの他の部分へのインタフェース (define (tag z) (attach-tag 'complex z)) (put 'add '(complex complex) (lambda (z1 z2) (tag (add-complex z1 z2)))) (put 'sub '(complex complex) (lambda (z1 z2) (tag (sub-complex z1 z2)))) (put 'mul '(complex complex) (lambda (z1 z2) (tag (mul-complex z1 z2)))) (put 'div '(complex complex) (lambda (z1 z2) (tag (div-complex z1 z2)))) (put 'make-from-real-imag 'complex (lambda (x y) (tag (make-from-real-imag x y)))) (put 'make-from-mag-ang 'complex (lambda (r a) (tag (make-from-mag-ang r a)))) (put 'equ? '(complex complex) (lambda (z1 z2) (equ-complex z1 z2))) ; 追加 (put '=zero? '(complex) (lambda (x) (=zero-complex x))) (put 'real-part '(complex) real-part) (put 'imag-part '(complex) imag-part) (put 'magnitude '(complex) magnitude) (put 'ange '(complex) angle) 'done) (define (make-complex-from-real-imag x y) ((get 'make-from-real-imag 'complex) x y)) (define (make-complex-from-mag-ang r a) ((get 'make-from-mag-ang 'complex) r a)) (install-scheme-number-package) (install-rational-package) (install-rectangular-package) (install-polar-package) (install-complex-package)
テスト
(=zero? 0) ; #t (=zero? 1) ; #f (=zero? (make-rational 0 3)) ; #t (=zero? (make-rational 0 0)) ; #f (=zero? (make-rational 1 0)) ; #f (=zero? (make-rational 1 3)) ; #f (=zero? (make-complex-from-real-imag 0 0)) ; #t (=zero? (make-complex-from-real-imag 0 1)) ; #f (=zero? (make-complex-from-real-imag 1 0)) ; #f (=zero? (make-complex-from-mag-ang 0.0 1.0)) ; #t