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What I am trying to do is create a copy of a Prolog instance and load that copy with JPL (the Java-Prolog Interface). I can think of several possible ways to do this, but none of them are completely worked out, and that is why I have come here.

First, I know I could save a copy of the state using qsave_program/2. This creates an exe file which I can run. However, I need to query this saved instance from Java using JPL. I've tried looking for documentation for this, but I couldn't find any (probably not a common issue). Is there any way I can run an instance saved using qsave_program/2 and query it from JPL?

The second idea would be to query the original instance for all dynamically asserted clauses. However, I cannot know what was asserted, so I cannot ask for those things directly, but rather I must collect these clauses based on the fact that they are dynamic. Then I could simply start another instance from JPL and assert these facts to create a copy. Is this possible? And would this effectively create a copy of the state?

Ben Mathers
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  • I thought of one possible solution, though it is certainly not pretty. I am in control of all the queries being sent through JPL. I could make a list of all the queries made, and whenever I create a new instance, make those same queries (and just ignoring the answers) to bring me to the same state I was before. – Ben Mathers Dec 02 '16 at 00:31

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Alright, here is the solution I've decided on. I can find all the predicates I will need to reassert with the following query:

predicate_property(X,dynamic),\+predicate_property(X,built_in),\+predicate_property(X,number_of_clauses(0)).

Here's why I think this will work for me. predicate_property(X,dynamic) will give me all the dynamic predicates. The reason I don't stop here is because there are a lot of predicates that are dynamic whose clauses I don't need to explicitly assert in my new instance of prolog. Predicates that have the property built_in can be ignored, because those will be automatically defined when I create the new instance of my prolog query. Even if they are explicitly defined by the user, that definition will be reinstantiated because I am consulting the same file. I can also ignore those predicates that have no clauses (number_of_clauses(0)), because the predicates are not affecting the state if they have no clauses.

So, once I have all the dynamic predicates I want, I can find all solutions to those predicates, make a list of the Terms returned in Java through JPL, open a new consultation of the file, and reassert those Terms.

Ben Mathers
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