Assignment 6 Solution

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[Question 1. 100 points] In class, we have shown you a program which mimics transactions done on a bank account. We will now develop an extended version of this example. For this we have rst de ned a data-type for transactions:

type transaction = Withdraw of int | Deposit of int | CheckBalance | ChangePassword of string | Close

We have added two new transactions to the example done in class.

In class, we de ned a function make-account which generates a bank account when given an opening balance.

In this exercise, you are asked to modify this code and generate a password-protected bank account. Any transaction on the bank account should only be possible, if one provides the right password. For this, implement the function makeProtectedAccount with the argu-ments and types shown below.

val makeProtectedAccount : int * string -> string * transaction -> unit = <fun>

This function takes in the opening balance as a rst argument and the password as a second, and will return a function which when given the correct password and a transaction will perform the transaction. One crucial di erence to be noted right away is that in the new code I want you to print the balance on the screen instead of returning it as a value.

Here are some examples.

  • let zoe = makeProtectedAccount(1000, “BiologyRocks”);; val zoe : string * transaction -> unit = <fun>

  • let elisa = makeProtectedAccount(500, “ArtsStudentsArePoor”);; val elisa : string * transaction -> unit = <fun>

  • let alison = makeProtectedAccount(2500, “MathIsTheBest”);;

val alison : string * transaction -> unit = <fun>

  • elisa(“ArtsStudentsArePoor”, Withdraw 100);; The new balance is: 400.- : unit = ()

  • alison(“MathIsTheBest”, Deposit 200);;

1

The new balance is: 2700.- : unit = ()

  • zoe(“BiologyRocks”, CheckBalance);; The balance is: 1000.- : unit = ()

  • zoe(“BiologySucks”, Withdraw 100);; Incorrect password.- : unit = ()

  • zoe(“BiologyRocks”, Withdraw 1500);; Insufficient funds.- : unit = ()

  • elisa(“ArtsStudentsArePoor”, ChangePassword “CSwillMakeMeRich”);; Password changed.- : unit = ()

  • elisa(“ArtsStudentsArePoor”, Deposit 100);;

Incorrect password.- : unit = ()

  • elisa(“CSwillMakeMeRich”, Deposit 200);; The new balance is: 600.- : unit = ()

  • alison(“MathIsTheBest”, Close);; Account successfully closed.- : unit = ()

  • alison(“MathIsTheBest”, CheckBalance);; Account closed.- : unit = ()

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