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Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
115 lines
3.2 KiB
Plaintext
115 lines
3.2 KiB
Plaintext
; feed/fanout — THE SHOWCASE. Fan activities out to followers via the APL outer
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; product (∘.×). activities ∘.× audience → an (activity × follower) matrix of
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; inbox events; flatten to a vector; guard-keep only real follow edges.
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;
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; Requires: lib/apl/runtime.sx, lib/feed/normalize.sx, lib/feed/stream.sx.
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;
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; NOTE: apl-outer's combiner result is run through (if (scalar? r) (disclose r) r).
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; A bare dict counts as a scalar (shape ()) and disclose nils it — so the combiner
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; must (enclose ...) its event dict; apl-outer then discloses it back intact.
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; --- graph: {followee -> (list of followers)} -------------------------------
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(define feed/followers (fn (graph user) (get graph user (list))))
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; build a graph from (follower followee) edges: "follower follows followee"
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(define
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feed/follow-graph
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(fn
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(edges)
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(reduce
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(fn
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(g e)
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(let
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((follower (first e)) (followee (nth e 1)))
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(assoc
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g
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followee
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(append (feed/followers g followee) (list follower)))))
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{}
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edges)))
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; --- helpers ----------------------------------------------------------------
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; unwrap an apl-scalar (has :ravel) back to its value; pass activities through
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(define
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feed/-val
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(fn
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(x)
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(if (and (= (type-of x) "dict") (has-key? x :ravel)) (disclose x) x)))
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(define feed/-elem? (fn (x lst) (some (fn (y) (equal? x y)) lst)))
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(define
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feed/-distinct
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(fn
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(lst)
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(if
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(= (len lst) 0)
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(list)
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(get (apl-unique (make-array (list (len lst)) lst)) :ravel))))
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; rank-2 matrix -> rank-1 stream of its ravel
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(define feed/-flatten (fn (arr) (feed/stream (get arr :ravel))))
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; distinct receivers across the whole graph, sorted for determinism
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; (dict key order is unspecified, so sort to pin audience/recipient ordering)
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(define
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feed/audience
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(fn
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(graph)
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(sort
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(feed/-distinct
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(reduce
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(fn (acc k) (append acc (feed/followers graph k)))
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(list)
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(keys graph))))))
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; --- the outer product ------------------------------------------------------
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; one (activity, follower) inbox event, enclosed so apl-outer keeps the dict
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(define feed/-mk-event (fn (a f) (enclose {:activity (feed/-val a) :to (feed/-val f)})))
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; keep events where :to actually follows the activity's actor
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(define
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feed/-edge?
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(fn
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(graph)
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(fn
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(ev)
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(feed/-elem?
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(get ev :to)
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(feed/followers graph (get (get ev :activity) :actor))))))
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; fanout — activities ∘.× audience, flatten, guard-keep real edges
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(define
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feed/fanout
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(fn
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(stream graph)
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(let
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((matrix (apl-outer feed/-mk-event stream (feed/stream (feed/audience graph)))))
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(feed/filter (feed/-flatten matrix) (feed/-edge? graph)))))
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; --- inbox queries ----------------------------------------------------------
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(define
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feed/inbox-for
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(fn
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(inbox user)
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(feed/filter inbox (fn (ev) (equal? (get ev :to) user)))))
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(define
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feed/recipients
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(fn
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(inbox)
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(feed/-distinct (map (fn (ev) (get ev :to)) (feed/items inbox)))))
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; the activities (unwrapped) destined for a user
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(define
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feed/inbox-activities
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(fn
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(inbox user)
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(map
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(fn (ev) (get ev :activity))
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(feed/items (feed/inbox-for inbox user)))))
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