Clojurians Log v2

Is there a way to have a short circuiting :or in clara, not sure why it is designed that way

@talgiat they aren’t meant for that. They are mostly just syntax sugar for multiple rules

In the case of you were sharing the stuff around the :or (prior conditions) and the RHS

you can implement a “short circuit ” pattern via multiple rules by making rules that are prioritized over one another

can you give an example?

here is one I made for unrelated reasons mostly https://gist.github.com/mrrodriguez/6a6f8373b25d69826b3efe154c928fac

I can probably do a shorter one in a min

yeah this example is in response to my colleague

we’re working on the same problem

just seems kinda hackish

also you need to know about the other rules

(r/defrule short-circuit
  [X] ;; whatever here
  =>
  (r/insert! <your fact here>
             :rule-marker/short-circuit))

(defrule fallback
  [:not [:rule-marker/short-circuit]]
  [Y]
  =>
  (r/insert! <your fact here>))

I see

I don’t know that I see it as hackish. I do understand it could be brittle to more rules added

here is what we have

`

(defrule premium-video [Video (= ?id id)] [:or [PremiumChannels (= id ?id)] [LessThanTwoHours (= id ?id)] [PremiumTopics (= id ?id)]] => (insert! (create-rule-result ->MarketplacePremiumVideoContent ?id (->Rule 1 “Premium Video” :points 6)))))

`

ignore the create rule-result

however a big short-circuiting :or would also be just order dependent on all the logic pushed into it

another thing you can do

Is let the :or fire as much as it can

then reconcile in a separate rule to “choose the best”

there is no best per se

they are all equal importance

so what is the reason to want short-circuit

Do you just not want multiple facts inserted?

`

(defrule premium-video
  [Video (= ?id id)]
  [:not [MarketplacePremiumVideoContent (= id ?id)]]
  [:or
    [PremiumChannels (= id ?id)]
    [LessThanTwoHours (= id ?id)]
    [PremiumTopics (= id ?id)]]
  =>
  (insert! (create-rule-result ->MarketplacePremiumVideoContent ?id (->Rule 1 "Premium Video" :points 6)))))

I tried this

but it went to an infinite loop

not sure why

yeah I just want one fact to be inserted

(r/defrule rule-with-or
  [:or
   [A]
   [B]
   [C]]
  =>
  (r/insert! (->FoundIt)))

(r/defrule aggregate-found
  [?found <- (acc/all) :from [FoundIt]]
 [:test (seq ?found)]
  =>
  (r/insert! (do-aggregation ?found)))

Insert a middle-fact

that you aggregate to a single fact

for “downstream” rules to only see 1 fact

this can be either a merge or just pick one if they are all the same, etc

(r/defrule aggregate-found
  [?found <- (acc/all) :from [FoundIt]]
 [:test (seq ?found)]
  =>
;; They are all the same, so I dont' care
  (r/insert! (first ?found)))

I should add a non-empty check to just avoid useless fires

> but it went to an infinite loop I believe your rule is invalidating itself

logically

however, I don’t know for sure not knowing what create-rule-result does

it just creates a record and adds some other metadata to it

if somehow the RHS (or later rule) leads to a MarketplacePremiumVideoContent to be inserted with that ?id then you’d get a loop

because it’d get inserted, which would make the :not become false

so it’d be retracted

but then :not would be true again, so it’d get reinserted, but then :not would be false again, so it’d be retracted - and repeat

I see

yeah, a bit of a mind bender

🙂

it’s best to try to think of the rules as declarative and order-independent

where possible

at least for people who are not used to rule engines or logic programming

and their job is to bring working memory into a steady and logically consistent state with all of the LHS of all rules

It can be a trick sometimes

the multiple inserts don’t impact our end results correctness

I just noticed it when testing and didn’t understand why

but thanks so much for the clarification

yeah, I find the “aggregating” to one idea common

I think the main takeaway is that the rules don’t short-circuit or control “duplcates” for you

it lets you decide what makes sense there

I’d say though, don’t be afraid to introduce “intermediate facts”

to tie multiple rules together

Yeah that makes sense

So rule-with-multiple-duplicate-inserts-possible and aggregate-the-duplicates rules with an intermediate/ephemeral fact between the two

then most other “downstream” rules just take the aggregated selection fact

Later on, there may be more complex reasoning in the aggregate-the-duplicates than just “take one”

yeah in our case it really doesn’t matter

if for example, they are no longer complete duplicates, or perhaps you want to count how many times it was “true” by counting the duplicates

sure

but I see the point

It’s been discussed before to have a working-memory-as-a-set sort of Clara mode

I just think it’ll helpful to have a real or

instead of doing the heavy lifting yourself

like a purposeful or

where there were never duplicates inserted, etc. Drools does that by default with logical insert (managed by truth maintenance). However, it does have a performance cost to manage a set for working memory (frequent hash code calculations etc) and also, it isn’t always what people want

sometimes “cardinality” of duplicate facts inserted can matter to the rule logic

true it can

Something like a “short circuit” or could be done

but can’t I control which behavior I want

Easiest would be to just have it generate several rules

that all do the “tiered” blocking pattern one one another

just generically

also, there is nothing stopping you from making a higher-level macro that did the short-circuit rule generation pattern to normal Clara rules

If you were sufficiently motivated and had enough places you foudn it useful hah

Yeah, can do a macro

Agreed on all @mikerod’s comments - I just wanted to mention that you don’t necessarily have to use a macro generating “defrule” calls, Clara can take rules as data structures if you prefer to go that way (easier in clj than cljs though)

It seems the infinite looping behavior has tripped a lot of people up - we should probably add a page to the http://clara-rules.org site on that somewhere. I’ve also logged an issue before to fail in that scenario analogously to StackOverflowException, just haven’t ever gotten around to it

My personal mental model of rules is (I think similar to his) that when using truth maintenance they are like statements that “for each join of things in these sets, these other things must exist”. Declarative logic, like SQL or even Excel