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Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
93 lines
2.4 KiB
Plaintext
93 lines
2.4 KiB
Plaintext
; feed/rank — scoring + ranking. Scorers are (activity -> number). Ranking is a
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; stable two-pass grade-down: first by :at descending (the tiebreak), then by
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; score descending — so ties resolve by recency, then by input order. Fully
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; deterministic on ties.
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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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; --- scorers ----------------------------------------------------------------
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; recency: half-life decay. score = 0.5 ^ (age / half-life). at==now -> 1.0.
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(define
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feed/recency
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(fn
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(now half-life)
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(fn (a) (expt 0.5 (/ (- now (get a :at)) half-life)))))
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; velocity: how many of this actor's activities fall in (at-window, at] —
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; a burst of recent activity scores higher.
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(define
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feed/velocity
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(fn
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(stream window)
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(fn
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(a)
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(len
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(filter
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(fn
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(b)
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(and
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(equal? (get b :actor) (get a :actor))
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(<= (get b :at) (get a :at))
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(> (get b :at) (- (get a :at) window))))
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(feed/items stream))))))
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; engagement: how many activities in the stream touch this activity's :object
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(define
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feed/engagement
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(fn
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(stream)
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(fn
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(a)
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(len
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(filter
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(fn (b) (equal? (get b :object) (get a :object)))
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(feed/items stream))))))
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; composite: weighted sum. parts = (list (list weight scorer) ...)
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(define
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feed/composite
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(fn
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(parts)
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(fn
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(a)
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(reduce
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(fn (acc p) (+ acc (* (first p) ((nth p 1) a))))
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0
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parts))))
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; --- ranking ----------------------------------------------------------------
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; stable reorder of items by key-fn, descending (grade-down is stable)
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(define
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feed/-desc-by
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(fn
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(items key-fn)
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(let
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((keys (make-array (list (len items)) (map key-fn items))))
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(let
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((order (get (apl-grade-down keys) :ravel)))
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(map (fn (i) (nth items (- i 1))) order)))))
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; rank by score descending; ties -> :at descending -> input order
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(define
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feed/rank
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(fn
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(stream score-fn)
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(let
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((by-at (feed/-desc-by (feed/items stream) feed/at)))
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(feed/stream (feed/-desc-by by-at score-fn)))))
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; attach a :score to each activity (for inspection / debugging)
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(define
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feed/with-scores
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(fn
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(stream score-fn)
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(feed/stream
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(map (fn (a) (assoc a :score (score-fn a))) (feed/items stream)))))
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; top-N ranked timeline
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(define
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feed/top
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(fn (stream score-fn n) (feed/take (feed/rank stream score-fn) n)))
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