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aspects

This example illustrates how to implement aspects (as in Aspect-Oriented Programming) using the event-driven programming support and hot patching using categories. The example reuses the bank money transfer AOP example as found in e.g.

https://en.wikipedia.org/wiki/Aspect-oriented_programming

The following entities are defined:

bank (object defining a bank with a transfer predicate)
accounts (category defining balance, withdraw, and deposit predicates)
jane and john (objects importing the accounts category)
security (hot patching category limiting maximum amount per transfer)
logging (event monitor object logging transfers) Note that we could also have defined security as a monitor object with a before/3 event handle that would make a transfer fail when the maximum amount is exceeded. The downside of this alternative is that we should not rely in the calling order of event handlers and thus the check could be applied before or after the logging message that a transfer is being attempted.
Print Logtalk, Prolog backend, and kernel versions (if running as a notebook):
```
%versions
```
Start by loading the example:
```
logtalk_load(aspects(loader)).
```
Transfer 100 from john account to jane account:
```
bank::transfer(john, jane, 100).
```


Try to transfer 400 from jane account to john account:
```
bank::transfer(jane, john, 400).
```