Clojurians Log v2

Newbie question... I'm struggling to write a rule which boils down to "This or that".

(defrecord This [x])
  (defrecord That [y])
  (defrule this-or-that
    "Print This if fact exists, else print That."
    [:or [?x <- This] [?x <- That]]
    =>
    (println :this-or-that ?x))

  (-> (mk-session 'labs-costs-clara.core)
      (insert
        (->This 1)
        (->That 2))
      (fire-rules))

This will print twice which isn't what I'm after.

(my real example is patching data... if X exists use it else use some other facts to fill in the gap)

ya, or isnt a xor, it can indeed follow both paths

i tend to think of it as if you had two disjunct rules

because that is pretty close to what it does

if you want one but not the other...well you are going to want to use two rules with :not on This in one and That on the other

That makes sense. My rules got a bit verbose which is what got me wondering.

Thanks

The only alternative I could imagine was some kind of maybe accumulator

(e.g. distinct but expecting one fact)

are you expecting only one, or potentially many

My code was really "if summary value exists use it, else calculate from many other facts" but that's not critical to the general question.

Thanks for your thoughts @zylox that makes me feel more confident

gotcha. id suggest something like

(defrule with-summary
  ""
  [Summary (= ?data data)]
  =>
  (println ?data))

(defrule without-summary
  ""
  [:not [Summary]]
  [?others <- (acc/all) :from [SecondaryFacts]]
  
  =>
  (println ?others))

best of luck

Thank you

without all the horrible syntax errors i just edited out haha