When using has_type/2 added more types via multifile which are working fine. Then wanted to use has_type(list(Type), X) :- is_list(X), element_types(X, Type). by calling has_type/2 from the module importing the library errors, and the code started failing. As near as I can figure, element_ty…

The issue seems to be :- begin_tests(example_bad). test(1) :- has_type(list(key_value),[kv(1,a),kv(2,b)]). :- end_tests(example_bad). error:has_type/2 is multifile, but not part of the interface of library(error). Type checking is done using must_be/2 (throws error) or is_of_type/2 (fails) …

[image] EricGT: Can use_module/2 be used to import predicates from modules that did not export the predicate? With a warning, yes. You should avoid warnings though :slight_smile: Otherwise it is not clear to me what you are trying to do. I see no reason for element_types/2 to be exported. …

[image] jan: Can you share the code you want to write? Yes I can, it will be large but let me ask this first. :smiley: I did make a complete minimal working example in the previous post, did you click on the triangle [image] to expand the section [image] … to see the code example?

Note on the example code. This clause: [image] EricGT: key_value_validate(Key_value) :- must_be(ground,Key_value), Key_value = kv(Key,Value), must_be(ground,Key), must_be(ground,Value). can be simplified to: key_value_validate(Key_value) :- must_be(ground,Key_value), …

Follow up for others interested in using library errors. I have been using library errors in creating some deterministic code (emulator) and found that there are two very different ways of using the type checking. is_of_type/2 fails and is useful with non-deterministic code. must_be/2 throws …

[image] EricGT: If you also read my other post, you know that I like algebraic data types and use to think they could not be done with SWI-Prolog until I found package typedef . I have not used it yet, but worth noting for others looking at using types with SWI-Prolog. Doesn’t parametric types…

[image] pmoura: Doesn’t parametric types gives you in practice the same expressive power of algebraic data types? I should know that, but I don’t. As such I will take some time to learn more about this and possibly add some links. ▶ tl;dr

[image] EricGT: If you also read my other post, you know that I like algebraic data types and use to think they could not be done with SWI-Prolog until I found package typedef . You can also use attributed variables to make algebraic data types. The example given in the link is pretty close. …

Using has_type(list(Type), X) with user created type not working as expected

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Using has_type(list(Type), X) with user created type not working as expected

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