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20 lines
889 B
20 lines
889 B
2 years ago
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Exercise 3.44: Consider the problem of
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transferring an amount from one account to another. Ben Bitdiddle claims that
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this can be accomplished with the following procedure, even if there are
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multiple people concurrently transferring money among multiple accounts, using
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any account mechanism that serializes deposit and withdrawal transactions, for
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example, the version of make-account in the text above.
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(define
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(transfer from-account to-account amount)
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((from-account 'withdraw) amount)
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((to-account 'deposit) amount))
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Louis Reasoner claims that there is a problem here, and that we need to use a
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more sophisticated method, such as the one required for dealing with the
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exchange problem. Is Louis right? If not, what is the essential difference
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between the transfer problem and the exchange problem? (You should assume that
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the balance in from-account is at least amount.)
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