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debug_hooks

This folder contains a very simple example of using the compiler flag hook/1 and the term expansion mechanism to either discard or activate debugging goals. For debugging goals in clause bodies, one defines clauses for goal_expansion/2. For debugging goals in directives (e.g., in the initialization/1 directive), one defines clauses for term_expansion/2.

We can use two hook objects, one for developing and debugging code and one for production code, or a single parametric object. This example illustrates both approaches although only the first one is used in the loader auxiliary files and in the sample queries.

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

%versions

Start by loading the example with the debug statements activated:

logtalk_load(debug_hooks(loader_debug)).

Debug the definition of the `object::append/3` predicate:

object::append([1,2,3], [4,5], List).

<!-- Recursive case: append([2, 3], [4, 5], _G340) Recursive case: append([3], [4, 5], _G347) Recursive case: append([], [4, 5], _G354) Base case: append([], [4, 5], [4, 5])

List = [1, 2, 3, 4, 5]. -->

Debug calls to the `object::sum/2` predicate:

object::sum([1,2,3,_], Sum).

<!-- Exception: error(instantiation_error, number::check(_G433), object) -->

object::sum([1,2,3,a], Sum).

<!-- Exception: error(type_error(number, a), number::check(a), object) -->

object::sum(wrong, Sum).

<!-- Exception: error(type_error(list, wrong), list::check(wrong), object) -->

Reload the example with the debug statements discarded:

logtalk_load(debug_hooks(loader_production)).

Call the `object::append/3` predicate without the debugging statements:

object::append([1,2,3], [4,5], List).

<!-- List = [1, 2, 3, 4, 5]. -->

Call the `object::sum/2` predicate without the debugging statements:

object::sum([1,2,3,_], Sum).

<!-- Exception: instantiation_error -->

object::sum([1,2,3,a], Sum).

<!-- Exception: type_error(evaluable, a/0) -->

object::sum(wrong, Sum).

<!-- false. -->