Add support for derived predicates

[Rezenders]

Add support for derived predicates

Related to #317

[fmrico]

Hi @Rezenders

Very interesting feature!! But I think it is not only being able to read a pddl file, but have it full functionality that includes:

• Read structure
• Show it in the PlanSys2 Terminal
• Add a getDeriveds() method to DomainExpertInterface.hpp and implement it at DomainExpertNode.hpp and DomainExpertClient.hpp
• AFAIK, a derived predicate adds a predicate to the problem when the expression is true, right? So, we should make a mechanism that, during the plan execution, for each new predicate, evaluate if a derived predicate can also be added.

Do you think we could use this PR to try to complete this list?

Thanks!!
Francisco

[Rezenders]

Hello @fmrico,

Thanks for the input!

Do you think we could use this PR to try to complete this list?

Sure :)

Add a getDeriveds() method to DomainExpertInterface.hpp and implement it at DomainExpertNode.hpp and DomainExpertClient.hpp

What do you think should be the return type of a getDerived method? Should we add a new Derived.msg? Something like:

plansys2_msgs/Node inferred_predicate
plansys2_msgs/Tree preconditions

AFAIK, a derived predicate adds a predicate to the problem when the expression is true, right?

Yeah, I believe that is probably how the planner handles derived predicates. @tobiaswjohn do you have any input on this?

So, we should make a mechanism that, during the plan execution, for each new predicate, evaluate if a derived predicate can also be added.

I am not sure I understood this part

[Rezenders]

Add a getDeriveds() method to DomainExpertInterface.hpp and implement it at DomainExpertNode.hpp and DomainExpertClient.hpp

This is supposed to be done. I still need to figure out a way to test the services.

PS: I had problems when derived predicates had exists conditions. It says it is not supported in PlanSys. I would also be interested in adding support for this, but I guess this can go in a separate issue/PR

ros2_planning_system/plansys2_pddl_parser/src/plansys2_pddl_parser/Exists.cpp

Lines 25 to 27 in a797196

	plansys2_msgs::msg::Node::SharedPtr Exists::getTree( plansys2_msgs::msg::Tree & tree, const Domain & d, const std::vector<std::string> & replace ) const {
	throw UnsupportedConstruct("Exists");
	}

[fmrico]

Hi @Rezenders

So, we should make a mechanism that, during the plan execution, for each new predicate, evaluate if a derived predicate can also be added.

I am not sure I understood this part

I suppose that, during the execution of a plan, if the expression of a derived predicate is true, we should add the predicate (the derived predicate), right? In that case, we should think on a runtime mechanism to do it.

PS: I had problems when derived predicates had exists conditions. It says it is not supported in PlanSys. I would also be interested in adding support for this, but I guess this can go in a separate issue/PR

Yes, it can go in a separate predicate.

Thanks!!! :)

[Rezenders]

I suppose that, during the execution of a plan, if the expression of a derived predicate is true, we should add the predicate (the derived predicate), right? In that case, we should think on a runtime mechanism to do it.

What if we just check if the derived predicates preconditions are satisfied when existPredicate is called?
Something like:

https://github.com/Rezenders/ros2_planning_system/blob/3156cba9a8a87fd3cd82bdcfb99ee6a48b0e4b31/plansys2_problem_expert/src/plansys2_problem_expert/ProblemExpert.cpp#L451-L463

I still need to test if this actually works.

[Rezenders]

I still need to test if this actually works.

I can't test with the setup I have because the planner I am using that supports derived predicates doesn't support durative actions. Related to issue #319

[Rezenders]

I don't think it is ready to merge.
The evaluation is not working when use_state is true.

[Rezenders]

The evaluation is not working when use_state is true.

I think this can be solved by returning the derived predicates with their preconditions fulfilled in getPredicates. Then when the evaluation is called with use_state true, if the predicates vector was "created" by calling getPredicates, it should work.

[fmrico]

Really good work, @Rezenders , congratulations.

Merging!!! 🚀