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missionary 2025-11-21
telekid 2025-11-21T20:23:14.982769Z
Missionary puzzle of the day 🧵
leonoel 2025-11-22T17:28:16.735239Z
Assuming input as sets
(require '[clojure.set :as set])
(defn differentiate [zero subtract]
(let [state (object-array 1)]
(aset state 0 zero)
(fn [curr]
(let [prev (aget state 0)]
(aset state 0 curr)
(subtract curr prev)))))
(defn set-diffs [x y]
(-> {}
(into (map (juxt identity (constantly true))) (set/difference x y))
(into (map (juxt identity (constantly false))) (set/difference y x))))
(defn set-events [flow-of-sets]
(m/ap (m/?> (m/seed ((differentiate {} set-diffs) (m/?> flow-of-sets))))))
(defn reconcile-merge [flow-of-sets-of-flows]
(m/ap (let [[flow lifecycle] (m/?> ##Inf (m/group-by key (set-events flow-of-sets-of-flows)))]
(try (if (m/?< (m/eduction (map val) (take 2) lifecycle))
(m/?> flow) (m/amb))
(catch Cancelled _ (m/amb))))))
(comment
(defn inner-flow [id]
(m/observe
(fn [!]
(prn id :up)
#(prn id :down))))
(def flow-1 (inner-flow 1))
(def flow-2 (inner-flow 2))
(def flow-3 (inner-flow 3))
(def flow-4 (inner-flow 4))
(def !active (atom #{flow-1}))
(def ps
((m/reduce (fn [_ x] (prn x)) nil
(reconcile-merge (m/watch !active)))
prn prn))
;; 1 :up
(reset! !active #{flow-1})
(reset! !active #{flow-1 flow-2 flow-3})
;; 2 :up
;; 3 :up
(reset! !active #{flow-2 flow-3})
;; 1 :down
(reset! !active #{flow-2 flow-4})
;; 3 :down
;; 4 :up
)telekid 2025-11-23T16:30:40.382089Z
How cool! Trying it out. Thanks as always.
telekid 2025-11-21T20:25:39.971719Z
Flow A is a flow of flows:
t0 [flow-1]
t1 [flow-1]
t2 [flow-1 flow-2 flow-3]
t3 [flow-2 flow-3]
t4 [flow-2 flow-4](run flow-a). At each emit of Flow A, I want run to start any added flows, and stop any removed flows:
t0 flow-1 ;; flow 1 starts
t1 | ;;
t2 flow-1 flow-2 flow-3 ;; flows 2 and 3 start
t3 | flow-3 ;; flow 1 stops
t4 flow-2 flow-4 ;; flow 3 stops; flow 4 starts
t5 ;; flows 2 and 4 stoprun's output flow.telekid 2025-11-21T20:32:47.982909Z
Been scratching my head on this one for a little bit
telekid 2025-11-21T20:55:41.655509Z
I feel like the secret is group-by
telekid 2025-11-21T20:55:57.146909Z
But I can't quite wrap my head around it
telekid 2025-11-21T21:53:25.670049Z
(Notes to self for monday) I think the solution to this problem is to create:
1. A map m mapping unique identities to flows
2. A function taking m and a flow of active-identities that, for each emission:
a. Starts flows associated with IDs in the current emit, but not in the previous one
b. Stops flows associated with IDs in the previous emit, but not in the current one
3. Probably some kind of combine argument that describes how to mix elements from activated flows