3.1.3. The Costs of Introducing Assignment
Exercise 3.7

Joint accounts

Consider the bank account objects created by make-account , with the password modification described in exercise 3.3 . Suppose that our banking system requires the ability to make joint accounts. Define a procedure make-joint that accomplishes this. Make-joint should take three arguments. The first is a password-protected account. The second argument must match the password with which the account was defined in order for the make-joint operation to proceed. The third argument is a new password. Make-joint is to create an additional access to the original account using the new password. For example, if peter-acc is a bank account with password open-sesame , then

(define paul-acc
    (make-joint peter-acc 'open-sesame 'rosebud))

will allow one to make transactions on peter-acc using the name paul-acc and the password rosebud . You may wish to modify your solution to exercise 3.3 to accommodate this new feature.

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