SICPゼミ第42回
練習問題4.7
(define (let*->nested-lets exp) (let ((defs (car exp)) (body (cdr exp))) (if (null? (cdr defs)) (list 'let (car defs) body) (list 'let (car defs) (let*->nested-lets (pair (cdr defs) body))))))
by dolicas
問題文で言ってる派生式でうまくいくはず．
練習問題4.8
(define (let->combination exp) (if (pair? (cadr exp)) (let->combination-prototype exp) (let* ((defs (let-defs exp)) (body (cadddr exp)) (func (make-lambda defs body))) (let->combination-prototype (list 'let (cons ((cadr exp) func) defs) body)))) (define (let->combination-prototype exp) (let ((defs (let-defs exp))) ((make-lambda (let-variable-from-defs defs) (let-body exp)) (let-defbody-from-defs defs)))) (define (let-defs exp) (cadr exp)) (define (let-body exp) (caddr exp)) (define (let-variable-from-defs defs) (if (null? defs) '() (cons (caar defs) (let-variable-from-defs (cdr defs))))) (define (let-defbody-from-defs defs) (if (null? defs) '() (cons (cdar defs) (let-variable-from-defs (cdr defs)))))
by dolicas
練習問題4.9
(define (for? exp) (tagged-list? exp 'for)) (define (for-initial exp) cadr) (define (for-terminate exp) caddr) (define (for-body exp) cadddr) (define (for->rec exp) (let->combination ('let for_iter ((i (for-initial exp))) (make-if (> i (for-terminate exp)) 'done (begin (for-body exp) (for_iter (+ i 1)))))))
by tube
練習問題4.10
(define (eval-if exp env) (if (true? (eval (if-predicate exp) env)) (eval (if-alternative exp) env) (eval (if-consequent exp) env)))
と変えるとifが逆になるという新しい文法のschemeになる．
SICPゼミ第41回
練習問題4.4
(define (eval-and exp env) (cond ((null? exp) #t) ((null? (cdr exp)) (eval (cdr exp) env)) ((not (eval (car exp) env)) #f) (else (eval-and (cdr exp) env)))) (define (and? exp) (tagged-list? exp 'and))
by dolicas
派生式の方もできた
(define (vars exp)) (define (and->if exp) (make-if (null? (vars exp)) #t (make-if (car (vars exp)) (and-if ('and (cdr (vars exp))) false))
by ぷに
練習問題4.5
(define (expand-clauses clauses) (if (null? clauses) 'false ; (let ((first (car clauses)) (rest (cdr clauses))) (if (cond-else-clause? first) (if (null? rest) (sequence->exp (cond-actions first)) (error "ELSE clause isn't last: COND->IF" clauses)) (make-if (cond-predicate first) (if (cond-test? (cond-actions first)) ((eval (cdr cond-actions) env) (eval cond-predicate env)) (sequence->exp (cond-actions first))) (expand-clauses rest)))))) (define (cond-test? clause) (= (cond-predicate clase) '=>))
と変更する
by dolicas
練習問題4.6
(define (let->combination exp) (let ((defs (let-defs exp))) ((make-lambda (let-variable-from-defs defs) (let-body exp)) (let-defbody-from-defs defs)))) (define (let-defs exp) (cadr exp)) (define (let-body exp) (caddr exp)) (define (let-variable-from-defs defs) (if (null? defs) '() (cons (caar defs) (let-variable-from-defs (cdr defs))))) (define (let-defbody-from-defs defs) (if (null? defs) '() (cons (cdar defs) (let-variable-from-defs (cdr defs)))))
SICPゼミ第40回
2章はやばいので4章に帰ってきました。
練習問題4.2
applicaionかどうかの判定 (application?) はタグを気にせずペアかどうかしか見ていない．これが最後でないと (define …) みたいなのも適用として扱ってしまうのでおかしくなる． call を使うことにするのであれば，ほかのやつと同じように，callというタグが付いてると思って扱えばよい．
by dolicas
練習問題4.3
(define (eval exp env) (if (self-evaluating? exp) exp (if (get 'eval (get-tag exp)) ((get 'eval (get-tag exp)) (get-content exp) env) (apply (eval (operator exp) env) (list-of-values (operands exp) env)) ) )) (define (get-tag exp) (car exp)) (define (get-content exp) (cdr exp))
by dolicas
SICPゼミ第38回
練習問題2.91
(define (install-polynomial-package) ;; 内部手続き ;; poly の表現 (define (make-poly variable term-list) (cons variable term-list )) (define (variable p) (car p)) (define (term-list p) (cdr p)) (define same-variable? eq?) (define variable? symbol?) ;; 項と項リストの表現 (define (add-poly p1 p2) (if (same-variable? (variable p1) (variable p2)) (make-poly (variable p1) (add-terms (term-list p1) (term-list p2))) (error "Polys not in same var: ADD-POLY" (list p1 p2)))) (define (add-terms L1 L2) (cond (( empty-termlist? L1) L2) (( empty-termlist? L2) L1) (else (let ((t1 (first-term L1)) (t2 (first-term L2))) (cond ((> (order t1) (order t2)) (adjoin-term t1 (add-terms (rest-terms L1) L2))) ((< (order t1) (order t2)) (adjoin-term t2 (add-terms L1 (rest-terms L2)))) (else (adjoin-term (make-term (order t1) (add (coeff t1) (coeff t2))) (add-terms (rest-terms L1) (rest-terms L2 ))))))))) (define (inversion termList) (if (empty-termlist? termList) termList (let ((term (first-term termList))) (if (eq? (type-tag term) 'polynomial) (adjoin-term (make-term (order term) (inversion (coeff term))) (inversion (rest-terms termList))) (adjoin-term (make-term (order term) (mul (make-scheme-number -1) (coeff term))) (inversion (rest-terms termList))))))) (define (mul-poly p1 p2) (if (same-variable? (variable p1) (variable p2)) (make-poly (variable p1) (mul-terms (term-list p1) (term-list p2))) (error "Polys not in same var: MUL-POLY" (list p1 p2)))) (define (mul-terms L1 L2) (if (empty-termlist? L1) (the-empty-termlist) (add-terms (mul-term-by-all-terms (first-term L1) L2) (mul-terms (rest-terms L1) L2)))) (define (mul-term-by-all-terms t1 L) (if (empty-termlist? L) (the-empty-termlist) (let ((t2 (first-term L))) (adjoin-term (make-term (+ (order t1) (order t2)) (mul (coeff t1) (coeff t2))) (mul-term-by-all-terms t1 (rest-terms L)))))) (define (adjoin-term term term-list) (if (=zero? (coeff term )) term-list (cons term term-list ))) (define (div-terms L1 L2) (if (empty-termlist? L1) (list (the-empty-termlist) (the-empty-termlist )) (let ((t1 (first-term L1)) (t2 (first-term L2))) (if (> (order t2) (order t1)) (list (the-empty-termlist) L1) (let ((new-c (div (coeff t1) (coeff t2))) (new-o (- (order t1) (order t2)))) (let ((rest-of-result (let ((rest (add-terms L1 (inversion (mul-terms L2 (list (make-term new-o new-c))))))) (div-terms rest L2)))) (cons (adjoin-term (make-term new-o new-c) (car rest-of-result)) (cdr rest-of-result)) )))))) (define (div-poly p1 p2) (if (same-variable? (variable p1) (variable p2)) (make-poly (variable p1) (div-terms (term-list p1) (term-list p2))) (error "Polys not in same var: ADD-POLY" (list p1 p2)))) (define (the-empty-termlist) '()) (define (first-term term-list) (car term-list )) (define (rest-terms term-list) (cdr term-list )) (define (empty-termlist? term-list) (null? term-list )) (define (make-term order coeff) (list order coeff )) (define (order term) (car term )) (define (coeff term) (cadr term )) ;; システムのほかの部分とのインターフェイス (define (tag p) (attach-tag 'polynomial p)) (put 'add '(polynomial polynomial) (lambda (p1 p2) (tag (add-poly p1 p2)))) (put 'mul '(polynomial polynomial) (lambda (p1 p2) (tag (mul-poly p1 p2)))) (put 'make 'polynomial (lambda (var terms) (tag (make-poly var terms )))) (put 'div '(polynomial polynomial) (lambda (p1 p2) (tag (div-poly p1 p2)))) 'done)
by tube
SICPゼミ第37回
練習問題2.88
install-polynomial-package内に以下の関数を追加する。
(define (inversion termList) (if (empty-termlist? termList) termList (let ((term (first-term termList))) (if (eq? (type-tag term) 'polynomial) (adjoin-term (make-term (order term) (inversion (coeff term))) (inversion (rest-terms termList))) (adjoin-term (make-term (order term) (mul (make-scheme-number -1) (coeff term))) (inversion (rest-terms termList)))))))
by pine
練習問題2.89
(define (install-polynomial-dense-package) ;; 内部手続き ;; poly の表現 (define (make-poly variable term-list) (cons variable term-list )) (define (variable p) (car p)) (define (term-list p) (cdr p)) (define same-variable? eq?) (define variable? symbol?) ;; 項と項リストの表現 (define (add-poly p1 p2) (if (same-variable? (variable p1) (variable p2)) (make-poly (variable p1) (add-terms (term-list p1) (term-list p2))) (error "Polys not in same var: ADD-POLY" (list p1 p2)))) (define (add-terms L1 L2) (cond (( empty-termlist? L1) L2) (( empty-termlist? L2) L1) (else (let ((t1 (first-term L1)) (t2 (first-term L2))) (cond ((> (order t1) (order t2)) (adjoin-term t1 (add-terms (rest-terms L1) L2))) ((< (order t1) (order t2)) (adjoin-term t2 (add-terms L1 (rest-terms L2)))) (else (adjoin-term (make-term (order t1) (add (coeff t1) (coeff t2))) (add-terms (rest-terms L1) (rest-terms L2 ))))))))) (define (inversion termList) (if (empty-termlist? termList) termList (let ((term (first-term termList))) (if (eq? (type-tag term) 'polynomial) (adjoin-term (make-term (order term) (inversion (coeff term))) (inversion (rest-terms termList))) (adjoin-term (make-term (order term) (mul (make-scheme-number -1) (coeff term))) (inversion (rest-terms termList))))))) (define (mul-poly p1 p2) (if (same-variable? (variable p1) (variable p2)) (make-poly (variable p1) (mul-terms (term-list p1) (term-list p2))) (error "Polys not in same var: MUL-POLY" (list p1 p2)))) (define (mul-terms L1 L2) (if (empty-termlist? L1) (the-empty-termlist) (add-terms (mul-term-by-all-terms (first-term L1) L2) (mul-terms (rest-terms L1) L2)))) (define (mul-term-by-all-terms t1 L) (if (empty-termlist? L) (the-empty-termlist) (let ((t2 (first-term L))) (adjoin-term (make-term (+ (order t1) (order t2)) (mul (coeff t1) (coeff t2))) (mul-term-by-all-terms t1 (rest-terms L)))))) (define (adjoin-term term term-list) (if (=zero? (coeff term )) term-list (cons (coeff term) term-list ))) (define (the-empty-termlist) '()) (define (first-term term-list) term-list) (define (rest-terms term-list) (cdr term-list )) (define (empty-termlist? term-list) (null? term-list )) (define (make-term order coeff) (list order coeff )) (define (order term) (- (length term) 1) (define (coeff term) (car term )) ;; システムのほかの部分とのインターフェイス (define (tag p) (attach-tag 'polynomial p)) (put 'add '(polynomial polynomial) (lambda (p1 p2) (tag (add-poly p1 p2)))) (put 'mul '(polynomial polynomial) (lambda (p1 p2) (tag (mul-poly p1 p2)))) (put 'make 'polynomial (lambda (var terms) (tag (make-poly var terms )))) 'done)
練習問題2.90
(install (dense-term-package) (put 'coeff 'term coeff-dense) ;他の関数もがんばる ;後で名前が衝突するので、2.89のはdenseとかつける ) (install (sparse-term-package) ;同上 ) (install (term-package) ;上の2つをinstall (define (coeff term) (apply-generic 'coeff term)) ;他の関数もがんばる。 )
SICPゼミ第36回
練習問題2.78からやり直し
練習問題2.78
(define (attach-tag type-tag contents) (if (eq? type-tag 'scheme-number) contents (cons type-tag contents ))) (define (type-tag datum) (if (pair? datum) (car datum) (if (number? datum) 'scheme-number (error "Bad tagged datum: TYPE-TAG" datum )))) (define (contents datum) (if (pair? datum) (cdr datum) (if (number? datum) datum (error "Bad tagged datum: CONTENTS" datum ))))続きを読む
