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sicp 3.3 的答案,我 输入错误password ,程序出错,后来看了win_hate 的答案
(define (make-account balance 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 pass m)
(cond ((not (eq? password pass)) (lambda (x) "Incorrect password"))
((eq? m 'withdraw) withdraw)
((eq? m 'deposit) deposit)
(else (error "Unkonwn request -- MAKE-ACCOUNT" m))))
dispatch)
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上面是 win_hate 的答案,我 的答案也差不 多,就 是在 dispatch 的 错误答案处理上直接(display "Incorrect password") , 没 (lambda(x) "Incorrect password")
这样的话 如果我输入错误的password , 我的 程序就会出错,
比如 ((acc 'love 'withdraw) 400)
Incorrect pasword. . procedure application: expected procedure, given: #<void>; arguments were: 400
谁解释一下,为社么一定要加个 lambda(x) 呢 。。 |
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