SICP_3.25
1 (define false #f)
2 (define true #t)
3
4 (define (make-table)
5 (let ((local-table (list '*table*)))
6
7 (define (assoc key records)
8 (cond ((null? records) false)
9 ((equal? (caar records) key) (car records))
10 (else (assoc key (cdr records)))))
11
12 (define (lookup keys)
13 (define (lookup-helper keys table)
14 (let ((subtable (assoc (car keys) (cdr table))))
15 (if subtable
16 (if (null? (cdr keys))
17 (cdr subtable)
18 (lookup-helper (cdr keys) subtable))
19 false)))
20 (lookup-helper keys local-table))
21
22 (define (insert! keys value)
23 (define (insert-helper! keys table)
24 (if (null? table)
25 (if (null? (cdr keys))
26 (cons (car keys) value)
27 (list (car keys) (insert-helper! (cdr keys) '())))
28 (let ((sub (assoc (car keys) (cdr table))))
29 (if sub
30 (if (null? (cdr keys))
31 (set-cdr! sub value)
32 (insert-helper! (cdr keys) sub))
33 (if (null? (cdr keys))
34 (set-cdr! table (cons (cons (car keys) value) (cdr table)))
35 (set-cdr! table (cons
36 (list (car keys)(insert-helper! (cdr keys) '()))
37 (cdr table))))))))
38 (insert-helper! keys local-table)
39 'ok)
40
41 (define (dispatch m)
42 (cond ((eq? m 'lookup-proc) lookup)
43 ((eq? m 'insert-proc) insert!)
44 (else (error "Unknow operation --TABLE" m))))
45
46 dispatch))
47
48 (define t1 (make-table))
49
50 ((t1 'insert-proc) '(key1 key2 key4) 5)
51
52 ((t1 'lookup-proc) '(key1 key2 key4))
?
轉載于:https://www.cnblogs.com/tclan126/p/6822909.html
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