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Web Studio

問題3.25

多次元の表を表現する。

(define (make-table)
  (let ((local-table (list '*table*)))
       (define (lookup key-list)
         (lookup-iter key-list local-table))
       (define (lookup-iter key-list local-table)
         (if (null? key-list)
             #f
             (let ((subtable (assoc (car key-list) (cdr local-table))))
                  (if subtable
                      (if (null? (cdr key-list))
                          (cdr subtable)
                          (lookup-iter (cdr key-list) subtable))
                      #f))))
       (define (insert! key-list value)
         (insert-iter! key-list value local-table))
       (define (insert-iter! key-list value local-table)
         (if (null? key-list)
             #f
             (let ((subtable (assoc (car key-list) (cdr local-table))))
                  (if subtable
                      (if (null? (cdr key-list))
                          (set-cdr! subtable value)
                          (insert-iter! (cdr key-list) value subtable))
                      (set-cdr! local-table
                                (cons (insert-iter key-list value)
                                      (cdr local-table))))))
         'ok)
       (define (insert-iter key-list value)
         (if (null? (cdr key-list))
             (cons (car key-list) value)
             (list (car key-list) (insert-iter (cdr key-list) value))))
       (define (print-table)
         local-table)
       (define (dispatch m)
         (cond ((eq? m 'lookup-proc) lookup)
               ((eq? m 'insert-proc!) insert!)
               ((eq? m 'print-table) print-table)
               (else (error "Unknown operation -- TABLE" m))))
       dispatch))

(define tb (make-table))
(define lookup (tb 'lookup-proc))
(define insert! (tb 'insert-proc!))
(define print-table (tb 'print-table))

(insert! '(japan tokyo 2009/2/13) 20.1)
(insert! '(japan osaka 2009/2/13) 22.0)
(insert! '(usa newyork 2009/2/13) 14.5)
(lookup '(japan tokyo 2009/2/13))
gosh> 20.1
(lookup '(japan osaka 2009/2/13))
gosh> 22.0
(lookup '(usa newyork 2009/2/13))
gosh> 14.5
(lookup '(usa tokyo 2009/2/13))
gosh> #f
(print-table)
gosh> (*table* (usa (newyork (|2009/2/13| . 14.5))) (japan (osaka (|2009/2/13| . 22.0)) (tokyo (|2009/2/13| . 20.1))))

計算機プログラムの構造と解釈

posted with amazlet at 08.11.07

ジェラルド・ジェイ サスマン ジュリー サスマン ハロルド エイブルソン
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