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# includes

This example illustrates using the `include/1` directive as both a file
directive and an entity directive. It also illustrates how to use this
directive to implement a simple persistency solution for an object
database.

Print Logtalk, Prolog backend, and kernel versions (if running as a notebook):

```logtalk
%versions
```

Start by loading the example:

```logtalk
logtalk_load(includes(loader)).
```

Test the use of the Logtalk `include/1` directive as a file directive:

```logtalk
findall(Vowel, vowel(Vowel), Vowels).
```

<!--
Vowels = [a,e,i,o,u].
-->

Test the use of the Logtalk `include/1` directive as an entity directive
by getting a list of all capitals:

```logtalk
countries::capitals(Capitals).
```

<!--
Capitals = [berlim, lisbon, madrid, paris, varsovia].
-->

Test the use of the Logtalk `include/1` directive as an entity directive
by getting sets of countries with the same population:

```logtalk
setof(Countries, countries::same_population(Countries), Solutions).
```

<!--
Solutions = [[france, poland], [germany, spain], [portugal]].
-->

Show the initial counter values, which may depend on previous runs:

```logtalk
counters::counter(Counter, Value).
```

<!--
Counter = a,
Value = ... ;
Counter = b,
Value = ... ;
Counter = c,
Value = ... ;
false.
-->

Increment one of the counters:

```logtalk
counters::inc_counter(b).
```

<!--
true.
-->

Save the counters database:

```logtalk
counters::save_counters.
```

<!--
true.
-->
