Recursion+backtracking doesn't work

[mpomarlan]

Try the following:

prolog->addPredicate("(apred ?x ?y)",
"(= ?x ?y)",
"(member ?x (0 2))");
prolog->addPredicate("(apred ?x ?y)",
"(= ?x ?y)",
"(member ?x (1 3))");
prolog->addPredicate("(apred ?x)",
"(apred ?x 2)");

solPrior = prolog->query("(apred ?x)", solPrior);
if(solPrior.valid())
std::cout << "BINDINGS " << solPrior.bindings().toString() << "\n";
}

Expected output: binding of ?x = 2. Produced output: no bindings (no valid solution found). This doesn't change if we switch the order of the predicate additions like this, however:

prolog->addPredicate("(apred ?x ?y)",
"(= ?x ?y)",
"(member ?x (1 3))");
prolog->addPredicate("(apred ?x ?y)",
"(= ?x ?y)",
"(member ?x (0 2))");
prolog->addPredicate("(apred ?x)",
"(apred ?x 2)");

so it's probably a recursion issue.

The next call (essentially, an unwrapping of the branch of apred that should work):

solPrior = prolog->query("(and (= ?x 2) (member ?x (0 2)))", solPrior);
if(solPrior.valid())
std::cout << "BINDINGS " << solPrior.bindings().toString() << "\n";
}

produces the expected binding of ?x = 2

[mpomarlan]

Now that I think about it, this is not as critical as it looks. I'll rewrite the forward planner in C++ so we can side-step this.

[fairlight1337]

Hm, that's odd. Okay, I'll have a closer look once I find some spare time this weekend (or on Monday, whatever happens first).

Thanks for figuring out the issue. This should actually work.