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From: [e-mail] (Dat Nguyen)
Newsgroups: comp.protocols.kermit.misc
Subject: Object-Oriented Programming in C-Kermit
Date: 14 Apr 2004 11:01:10 -0700
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Xref: newsmaster.cc.columbia.edu comp.protocols.kermit.misc:14924

Yesteryear many software went object-oriented (even Pascal, Cobol and
Assembler). Today Patterns is the way to go.

C-Kermit does not provide built-in OOP environment, but its dynamic
evaluation of expressions can be exploited to do OOP and Patterns.
The following script provides the OOP environment in C-Kermit (8.x):

    ftp://kermit.columbia.edu/kermit/scripts/ckermit/class

In this installment I use C-Kermit to implement the BankAccount class
described by John Maloney in:

    http://www.squeak.org/tutorials/BankAccount.html

In Smalltalk, the BankAccount class is defined as:

Object subclass: #BankAccount

        instanceVariableNames: 'balance'

        classVariableNames: ''

        poolDictionaries: ''

        category: 'My Stuff'

In C-Kermit, with the support of the script 'class', the BankAccount
class is defined as:

    class BankAccount

In C-Kermit, the instanceVariable 'balance' is created and initialized
with 0 when an object of BankAccount is instantiated with the class
method:

    define BankAccount::new: {
        _asg \%1.balance 0
        (\%1)
    }

In Smalltalk, a new object of BankAccount is created as follows:

    b := BankAccount new

In C-Kermit:

    BankAccount new: b



The Smalltalk method to retrieve the balance is:

    balance

       "Return the balance"

       ^ balance

In C-Kermit:

    define BankAccount>>balance {
        (\%1.balance)
    }

and Smalltalk retrieves the balance of the account b as follows:

    b balance

In C-Kermit:

    b balance

To store that balance in a variable theBalance in C-Kermit:

    (setq theBalance (b 'balance))



The Smalltalk method to deposit an amount into an account is:

    deposit: amount

        balance _ balance + amount.

in C-Kermit:

    define BankAccount>>deposit: {
        (++ \%1.balance \%2)
        (\%1)
    }

and Smalltalk deposits an amount 100 into the account b as follows:

    b deposit: 100

in C-Kermit:

    b deposit: 100



The Smalltalk method to withdraw an amount from an account is:

    withdraw: amount

        amount > balance ifTrue: [

                ^ self inform: 'sorry, not enough funds'].

        balance _ balance - amount.

in C-Kermit:

    define BankAccount>>withdraw: {
        if < \m(\%1.balance) \%2 END -1 NOT ENOUGH BALANCE
        (-- \%1.balance \%2)
        (\%1)
    }

and Smalltalk withdraws an amount 50 from the account b as follows:

    b withdraw: 50

in C-Kermit:

    b withdraw: 50

like in Smalltalk, in C-Kermit messages can be cascaded sending to an
object as follows:

    ((((BankAccount 'new: 'Bell) 'deposit: 500) 'withdraw: 150) 'balance)

which creates a new account Bell, deposits 500 to it, withdraws 150
from it and retrieves the balance from it.

To recap, follows is a rudimentary BankAccount application in
C-Kermit:



    take class

    class BankAccount

    define BankAccount::new: {
        _asg \%1.balance 0
        (\%1)
    }

    define BankAccount>>balance {
        (\%1.balance)
    }

    define BankAccount>>deposit: {
        (++ \%1.balance \%2)
        (\%1)
    }

    define BankAccount>>withdraw: {
        if < \m(\%1.balance) \%2 END -1 NOT ENOUGH BALANCE
        (-- \%1.balance \%2)
        (\%1)
    }


    BankAccount new: Rich

    (Rich 'balance)

    Rich deposit: 1000000

    (Rich 'balance)

    Rich withdraw: 1

    (Rich 'balance)

    BankAccount new: Poor

    (Poor 'balance)

    Poor deposit: 5

    (Poor 'balance)

    Poor withdraw: 11

    ((((BankAccount 'new: 'Bell) 'deposit: 500) 'withdraw: 150) 'balance)




This program is object-oriented, very Smalltalk look alike. All
C-Kermit particular syntaxes are wrapped in the methods of the class,
and the new S-Espressions are very usefull for this style of
programming.

Dat Nguyen