single facts are automatically retracted when a new fact is asserted.

But in general I think you should use fact variables:
See also Facts, and it is also a good idea to follow the tutorials.

See also Debugging tips: nothing.

Considering what I think you ask the short answer is no . Assume this: interface window ... end interface window interface control supports window ... end interface control class textControl : control ... end class textControl We have a class textControl which constructs objects of the interface typ...

A typeLibrary is a runtime representation of a type, it is only documented in form of the corresponding interface ($(ProDir)\pfc\reflection\typeLibrary\typeLibrary.i).

Type libraries are used heavily behind the scenes to make polymorphism work. But I doubt that you will need it for anything.

While vpi::processEvents will help to update the windows, it will also allow users to press on menu-entries, buttons, etc. So it may mix other processing in the "current" one, hence it has many aspects in common with multi-threaded programming or (more precisely) coroutines and asynchronou...

You can also use orelse:

Sorry, I typed the wrong predicate, it should be:

Given that the format match that of a Visual Prolog number you can use:
where integer could instead be for example real.

The build-in predicate typeLibraryOf can give you the typeLibrary of any term. That will give you the type which it has "here" But it seems you are looking for the construction type and that can unfortunately not be found by reflection/introspection. But if you have a suspicion about the t...

Please read about [code] ... [/code] formatting in the forum guides.

I m not sure I understand what you mean, perhaps you could give more details?

The brief answer is: You cannot use this code in Visual Prolog. (You can however (I guess/believe) run it in our PIE program (Prolog Interpreter Engine), which is an example program comes with Visual Prolog that implements a classical Prolog system much closer to ISO Prolog). I don't know how much o...

I guess that you didn't declare the fact variable in the implementation:

The predicate removeAllBy is used when you want to supply your own comparison routine. For strings it could for example (as above) be a comparison that consider uppercase and lowercase letters the same. But for numbers it would (almost always) be natural to use the normal number comparison. clauses ...

I am afraid I will have to disappoint you. There is no dark theme, and actually no color configurations at all.

I realize that "night programmers" prefer dark themes, but we have never got around to support it.