A simple bank account class:
(class bank-account
((mutable balance))
((deposit amount)
(balance! (+ balance amount)))
((withdraw amount)
(when (> amount balance)
(error #t "Account overdrawn"))
(balance! (- balance amount))))
The class has a single mutable field balance and two methods, deposit and withdraw.
Make a new bank-account:
> (define b0 (make-bank-account 0))
Declare that the variable is a bank-account:
> (is-bank-account b0)
Look at the balance:
> b0.balance
0
Deposit money:
> (b0.deposit 100)
Verify the deposit:
> b0.balance
100
Withdraw money:
> (b0.withdraw 50)
Look at the new balance:
> b0.balance
50
Ask for more than is in the account:
> (b0.withdraw 500)
Unhandled exception
Condition components:
1. &error
2. &who: #t
3. &message: "Account overdrawn"
4. &irritants: ()
The methods are available as procedures bank-account::deposit and bank-account::withdraw. Example:
> (bank-account::deposit b0 100)
Verity the deposit:
> b0.balance
150
This wacky experiment is available in the (dharmalab records class) library.