Clara-rules typical logical loop

clara-logical-loop.situation.clj

;; Usually the solution is to reframe the problem you have in a way that avoids the logical contradiction, 
;; ie. 'not B => B'
;; and continue to use the default inserts (not unconditional type) that participate in truth maintenance

;; To avoid a rule like this:
(r/defrule b-contradiction
 [A]
 [:not [B]]
 =>
 (r/insert! (->B))        

;; I think that situation often comes up when you are attempting to have “uniqueness” in your inserts
;; ie. you don’t want to insert B multiple times.
;; A way to work around that, is to insert some intermediary fact type, 
;; eg. BCandidate, with no cardinality concerns.
;; Then have an aggregate rule that takes all BCandidates and aggregates it to a single B fact - 
;; so you end up with the single cardinality/unique B fact for later rules to reason about.

(r/defrule find-b-candidates
 [A]
 =>
 ;; Do something with A data if needed here
 (r/insert! (->BCandidate))

(r/defrule process-b-candidates
 ;; If there are join criteria with another fact type, like A, then that could be used here to filter
 ;; through the candidates.
 [?bcs <- (acc/all) :from [BCandidate]]
 =>
 ;; Build B however, is appropriate based on the candidate collection; using `first` here for demo
 (r/insert! (-> ?bcs first map->B)))