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# expansion

The `expansion.lgt` source file illustrates how the scope of the term and
goal-expansion predicates affects the results of the expansion mechanisms.

The `hooks.lgt` and `raw.lgt` source files illustrate how to define and
combine hook objects.

The `pipeline.lgt` source file uses the `hook_pipeline/1` library object,
which illustrates how to define a hook object that applies a pipeline of
hook objects.

For more details, please see the comments in the source files.

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

```logtalk
%versions
```

Start by loading the example:

```logtalk
logtalk_load(expansion(loader)).
```

Simple tests of the `expand_term/2` and `expand_goal/2` built-in methods.

Sending the messages `expand_term/2` (`expand_goal/2`) to an object only
result in the use of the clauses defined for the `term_expansion/2` 
(`goal_expansion/2`) hook predicate if this predicate is public:

```logtalk
exp_public::expand_term(8, Term).
```

<!--
Term = eight.
-->

```logtalk
exp_public::expand_goal(write(Term), EGoal).
```

<!--
EGoal = write_term(Term, [quoted(true)]).
-->

The clauses for the `term_expansion/2` (`goal_expansion/2`) hook predicate
will not be used if they are not within the scope of the sender (in this
case, the pseudo-object `user`) as in the following cases:

```logtalk
exp_protected::expand_term(8, Term).
```

<!--
Term = 8.
-->

```logtalk
exp_protected::expand_goal(write(Term), EGoal).
```

<!--
EGoal = write(Term).
-->

```logtalk
exp_private::expand_term(8, Term).
```

<!--
Term = 8.
-->

```logtalk
exp_private::expand_goal(write(Term), EGoal).
``` 

<!--
EGoal = write(Term).
-->

The following queries perform similar tests but with the calls to the
`expand_term/2` (`expand_goal/2`) built-in method being made from within 
the prototypes:

```logtalk
desc_public::test_term_expansion(8, Term).
```

<!--
Term = eight.
-->

```logtalk
desc_public::test_goal_expansion(write(Term), EGoal).
```

<!--
EGoal = write_term(Term, [quoted(true)])
```

<!--
true.
-->

```logtalk
desc_protected::test_term_expansion(8, Term).
```

<!--
Term = eight.
-->

```logtalk
desc_protected::test_goal_expansion(write(Term), EGoal).
```

<!--
EGoal = write_term(Term, [quoted(true)]).
-->

```logtalk
desc_private::test_term_expansion(8, Term).
```

<!--
Term = 8.
-->

```logtalk
desc_private::test_goal_expansion(write(Term), EGoal).
```

<!--
EGoal = write(Term).
-->

Simple tests of hook objects:

```logtalk
cooked << (aa, bb, cc).
```

<!--
true.
-->

```logtalk
cooked << (ha, hb, hc).
```

<!--
true.
-->

```logtalk
cooked << p.
```

<!--
true.
-->

```logtalk
piped<<a(key-value).
```

<!--
true.
-->

```logtalk
piped<<b(key-value).
```

<!--
true.
-->

```logtalk
piped<<c(key-value).
```

<!--
true.
-->
