GNU Smalltalk User’s Guide: Moving money around

6.4.6 Moving money around

We can now create accounts, and look at them. As it stands, though, our balance will always be 0—what a tragedy! Our final methods will let us deposit and spend money. They’re very simple:

 Account extend [
 spend: amount [
 <category: 'moving money'>
 balance := balance - amount
 ]
 deposit: amount [
 <category: 'moving money'>
 balance := balance + amount
 ]
 ]

With these methods you can now deposit and spend amounts of money. Try these operations:

 a deposit: 125
 a deposit: 20
 a spend: 10