SICP問題2.85
オブジェクトを塔に沿って下へ「押す」汎用演算projectの定義
(define (project x) (let ((proc (get 'project (type-tag x)))) (if proc (proc (contents x)) #f)))
オブジェクトを出来るだけ下げるdrop手続き
(define (drop x) ;; 文字列または数値が同じか? (define (val-eq? x y) (if (and (number? x) (number? y)) (= x y) (equal? x y))) ;; リストの内容が同じか? (define (cnt-eq? x y) (cond ((and (null? x) (null? y)) #t) ((and (and (pair? x) (pair? y)) (val-eq? (car x) (car y))) (cnt-eq? (cdr x) (cdr y))) (else (val-eq? x y)))) ;; 本体 (let ((projected (project x))) (if projected (let ((raised (raise projected))) (let ((xt (type-tag x)) (xc (contents x)) (rt (type-tag raised)) (rc (contents raised))) (if (and (equal? xt rt) (cnt-eq? xc rc)) (drop projected) x))) x)))
dropを使用したapply-generic
(define (apply-generic op . args) (let ((type-tags (map type-tag args))) (let ((proc (get op type-tags))) (if proc (apply proc (map contents args)) (let ((dropped-args (map drop args))) (let ((dropped-tags (map type-tag dropped-args))) (let ((dropped-proc (get op dropped-tags))) (if dropped-proc (apply dropped-proc (map contents dropped-args)) (error "No method for these types -- APPLY-GENERIC")))))))))
それぞれの手続き
(define (install-integer-package) (define (tag x) (attach-tag 'integer x)) (define (integer->rational n) (make-rational n 1)) (put 'add '(integer integer) (lambda (x y) (tag (+ x y)))) (put 'sub '(integer integer) (lambda (x y) (tag (- x y)))) (put 'mul '(integer integer) (lambda (x y) (tag (* x y)))) (put 'div '(integer integer) (lambda (x y) (tag (/ x y)))) (put 'equ? '(integer integer) (lambda (x y) (= x y))) (put '=zero? '(integer) (lambda (x) (= x 0))) (put 'make 'integer (lambda (x) (tag x))) (put 'exp '(integer integer) (lambda (x y) (tag (expt x y)))) (put 'raise 'integer (lambda (x) (integer->rational x))) 'done) (install-integer-package) (define (make-integer n) ((get 'make 'integer) 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)))) (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)) (define (rational->real x) (make-real (/ (numer x) (denom x)))) ; 追加 (define (rational->integer x) (make-integer (round (/ (numer x) (denom 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))) (put '=zero? '(rational) (lambda (x) (=zero-rat x))) (put 'make 'rational (lambda (n d) (tag (make-rat n d)))) (put 'raise 'rational (lambda (x) (rational->real x))) ; 追加 (put 'project 'rational (lambda (x) (rational->integer x))) 'done) (define (make-rational n d) ((get 'make 'rational) n d)) ;; 実数パッケージ (define (install-real-package) (define (tag x) (attach-tag 'real x)) (define (real->complex x) (make-complex-from-real-imag x 0)) ; 追加 ; とりあえず小数点以下の桁数を5桁位で考えておく (define (real->rational x) (make-rational (* x 100000) 100000)) (put 'add '(real real) (lambda (x y) (tag (+ x y)))) (put 'sub '(real real) (lambda (x y) (tag (- x y)))) (put 'mul '(real real) (lambda (x y) (tag (* x y)))) (put 'div '(real real) (lambda (x y) (tag (/ x y)))) (put 'equ? '(real real) (lambda (x y) (= x y))) (put '=zero? '(real) (lambda (x) (= x 0))) (put 'make 'real (lambda (x) (tag (* x 1.0)))) ;; rational->real で 1/3 とかになってしまうのでごまかし (put 'exp '(real real) (lambda (x y) (tag (expt x y)))) (put 'raise 'real (lambda (x) (real->complex x))) (put 'project 'real (lambda (x) (real->rational x))) 'done) (install-real-package) (define (make-real x) ((get 'make 'real) x)) ; 複素数の直交座標パッケージと極座標パッケージ ; 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) ; 極座標の場合 (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)))) (define (=zero-complex z) (and (= (real-part z) 0) (= (imag-part z) 0))) ;; 追加 (define (complex->real z) (make-real (real-part z))) ;; 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))) (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) ;; 追加 (put 'project 'complex (lambda (x) (complex->real x))) '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-integer-package) (install-rational-package) (install-real-package) (install-rectangular-package) (install-polar-package) (install-complex-package)
テスト
(add (make-integer 3) (make-real 5.0)) ; (integer . 8.0) (add (make-integer 3) (make-real 5.5)) ; *** ERROR: No method for these types -- APPLY-GENERIC ; Stack Trace: ; _______________________________________ (add (make-rational 1 3) (make-real 5.5)) ; (rational 35.0 . 6.0) (add (make-rational 3 1) (make-real 5.5)) ; *** ERROR: No method for these types -- APPLY-GENERIC ; Stack Trace: ; _______________________________________ (add (make-complex-from-real-imag 5 0) (make-real 5)) ; (integer . 10.0) (add (make-complex-from-real-imag 5 0) (make-real 5.0)) ; (integer . 10.0) (add (make-complex-from-real-imag 5.5 0) (make-real 5.0)) ; *** ERROR: No method for these types -- APPLY-GENERIC ; Stack Trace: ; _______________________________________
OKなんだけど、先にdropで切り下げてるので、本当は演算できるはずなのがうまくいかない。