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問題3.24

(define (make-table same-key?)
  (let ((local-table (list '*table*)))
       (define (lookup key-1 key-2)
         (let ((subtable (same-key? key-1 (cdr local-table))))
              (if subtable
                  (let ((record (same-key? key-2 (cdr subtable))))
                       (if record
                           (cdr record)
                           #f))
                  #f)))
       (define (insert! key-1 key-2 value)
         (let ((subtable (same-key? key-1 (cdr local-table))))
              (if subtable
                  (let ((record (same-key? key-2 (cdr subtable))))
                       (if record
                           (set-cdr! record value)
                           (set-cdr! subtable
                                     (cons (cons key-2 value)
                                           (cdr subtable)))))
                  (set-cdr! local-table
                            (cons (list key-1
                                        (cons key-2 value))
                                  (cdr local-table)))))
         'ok)
       (define (dispatch m)
         (cond ((eq? m 'lookup-proc) lookup)
               ((eq? m 'insert-proc!) insert!)
               (else (error "Unknown operation -- TABLE" m))))
       dispatch))

(define (search key records)
  (cond ((null? records) #f)
        ((equal? key (caar records)) (car records))
        ((and (number? key) (< (abs (- key (caar records))) 0.5)) (car records))
        (else (search key (cdr records)))))

(define tb3 (make-table search))
(define insert! (tb3 'insert-proc!))
(define lookup (tb3 'lookup-proc))
(insert! 'tokyo 10.5 '2009/2/15)
(insert! 'tokyo 20.1 '2009/4/25)
(insert! 'osaka 12.8 '2009/1/5)
(insert! 'osaka 21.1 '2009/4/10)
(insert! 'osaka 30.2 '2009/7/24)
(lookup 'tokyo 10.5)
gosh> |2009/2/15|
(lookup 'osaka 21.0)
gosh> |2009/4/10|
(lookup 'osaka 40.0)
gosh> #f
(lookup 'tokyo 20.0)
gosh> |2009/4/25|
(lookup 'osaka 20.0)
gosh> #f

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
ピアソンエデュケーション
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