58 lines
1.6 KiB
Racket
58 lines
1.6 KiB
Racket
#lang sicp
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(#%require racket/trace)
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(define (make-table)
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(list '*table*))
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(define (assoc key records)
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(cond ((null? records) false)
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((equal? key (caar records)) (car records))
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(else (assoc key (cdr records)))))
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(define (empty? table)
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(not (list? (cdr table))))
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(define (lookup keys table)
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(cond ((null? keys) (cdr table))
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((empty? table) false)
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(else
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(let ((subtable (assoc (car keys) (cdr table))))
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(if subtable
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(lookup (cdr keys) subtable)
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false)))))
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(define (insert! keys value table)
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(define (insert-subtable! keys subtable)
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(if (and (not (null? keys))
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(not (null? subtable)))
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(let* ((key (car keys))
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(record (assoc (car keys) (cdr subtable))))
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(if record
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(if (= (length keys) 1)
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(set-cdr! record value))
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(set-cdr! subtable
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(cons (cons key
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(if (= (length keys) 1)
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value
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'()))
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(cdr subtable))))
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(let ((next-subtable (assoc key (cdr subtable))))
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(insert-subtable! (cdr keys) next-subtable)))))
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(insert-subtable! keys table)
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'ok)
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(#%require (only racket/base module+))
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(module+ test
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(#%require rackunit)
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(test-begin
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(define t (make-table))
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(insert! '(10 10) 'a t)
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(check-equal? (lookup '(10 10) t) 'a)
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(check-equal? (lookup '(10 10 10) t) false)
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(insert! '(20) 'b t)
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(check-equal? (lookup '(20) t) 'b)))
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