I get to be amazed I understand as much as I do. I declare you an honorary masochist by virtue of coding Perl.

I'm still working through it, particularly trying to understand what it is supposed to look like and behave like, and noticed something which _might_ be of service:

If I understand it correctly, the _add_level method currently overwrites facts with the same first element. I imagine I'm trouncing all over established terminology, so let me illustrate instead.

You have the two facts:

$pg->add_fact( gnarfle => qw/ foo bar baz / );
$pg->add_fact( gnarfle => qw/ foo tac toe / );
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           {
            '2' => [
                     undef,
                     {
                       '3' => 3
                     },
                     {
                       '4' => 4
                     }
                   ]
          }
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But after the foo bar baz rule begins, it looks like a terribly disappointing

          {
            '2' => []
          }
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which is then fleshed out with the 5 and 6 entries. After it's done, instead of {foo => [undef,tac,toe]}, it's {foo => [undef,bar,baz]}

The end result is that you lose part of the tree, and no longer get full results from doing rule requests.

You've probably already noticed this one, and I don't yet have enough clue to fix it correctly (I have a feeling it'll require a data structure tweak, and I don't know enough about the module to do it yet). If this was confusing anyone else, I hope I've explained what was happening.

I just learned about Data::Dumper::Deepcopy - useful when Dumper decides that all undefs are actually a reference to the same element. That was confusing, too.

Thanks for the puzzle, Ovid!

--Ferret