I need to run a ruleset, and for each rule that doesn't pass, I need to know why (via error message). Is it possible to implement rules which pass when finding facts, but generate an error when they don't? At first I thought it was a simple as this:

engine = Wongi::Engine.create
debit_rule = engine.rule "transaction type is debit" do
   forall {
     has :TRANSACTION, :transaction_type, :TX_TYPE
     equal :TX_TYPE, 2
   }
   make {
     error "Transaction is not a debit"
   }
end

engine << ["A", :transaction_type, 1]

But after scratching my head for a while, I eventually learned that this will throw an error if the forall finds those facts. I could negate the conditions in the forall, but I'd really rather have the conditions in the positive, since I feel like it reads better.

Any ideas?