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Exersise 3.3

make-account関数にパスワード機能を追加する。

 (define (make-account balance password)
   (let ((saved-password ""))
     (define (withdraw amount)
       (if (>= balance amount)
       (begin (set! balance (- balance amount))
          balance)
       "Insufficient funds"))
     (define (deposit amount)
       (set! balance (+ balance amount))
       balance)
     (define (dispatch password m)
       (if (equal? saved-password password)
       (cond ((eq? m 'withdraw) withdraw)
         ((eq? m 'deposit) deposit)
         (else (error "Unknown request -- MAKE-ACCOUNT"
                  m)))
       (error "Incorrect password")))
   (begin (set! saved-password password)
      dispatch)))
 
 (use gauche.test)
 (test-start "Exersise 3.3")
 (define acc (make-account 100 'secret-password))
 (test* "withdraw" 60 ((acc 'secret-password 'withdraw) 40))
 (test* "deposit" 110 ((acc 'secret-password 'deposit) 50))
 (test* "error" *test-error*  ((acc 'some-other-password 'deposit) 50))
 (test-end)