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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):

%versions

Start by loading the example:

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:

exp_public::expand_term(8, Term).

<!-- Term = eight. -->

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:

exp_protected::expand_term(8, Term).

<!-- Term = 8. -->

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

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

exp_private::expand_term(8, Term).

<!-- Term = 8. -->

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:

desc_public::test_term_expansion(8, Term).

<!-- Term = eight. -->

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. -->

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

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

desc_private::test_term_expansion(8, Term).

<!-- Term = 8. -->

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

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

Simple tests of hook objects:

cooked << (aa, bb, cc).

<!-- true. -->

cooked << (ha, hb, hc).

<!-- true. -->

cooked << p.

<!-- true. -->

piped<<a(key-value).

<!-- true. -->

piped<<b(key-value).

<!-- true. -->

piped<<c(key-value).

<!-- true. -->