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view.sx: persist/view bundles stream + fold + snapshot name; view-attach subscribes it to a hub so each publish refreshes the snapshot incrementally, making view-peek an O(1) current read. view-value always folds the tail so it is never stale. The consumer read-model abstraction (feed indices, audit rollups, search counters). 122/122. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
50 lines
1.6 KiB
Plaintext
50 lines
1.6 KiB
Plaintext
; persist/view — a materialized view: the consumer-facing read model. It bundles
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; a stream, a fold (step + seed) and a snapshot name. Attached to a hub it
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; refreshes incrementally on every publish, so the materialized value stays
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; current on write and reads are O(1) snapshot loads (persist/view-peek) instead
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; of a full fold. This is what feed indices, mod audit rollups, search counters,
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; etc. sit on. Requires: lib/persist/snapshot.sx, lib/persist/subscribe.sx.
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(define persist/view (fn (name stream step seed) {:name name :step step :stream stream :seed seed}))
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(define persist/view-name (fn (v) (get v :name)))
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(define persist/view-stream (fn (v) (get v :stream)))
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; bring the view's snapshot up to date with the log tail; returns the state
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(define
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persist/view-refresh
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(fn
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(b v)
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(persist/checkpoint
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b
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(get v :stream)
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(get v :name)
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(get v :step)
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(get v :seed))))
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; current materialized value — refreshes first, so never stale
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(define
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persist/view-value
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(fn (b v) (persist/project-value (persist/view-refresh b v))))
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; O(1) read of the last persisted snapshot value WITHOUT folding the tail. Equal
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; to view-value when the view is attached (kept current on every publish);
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; otherwise may lag the log by the un-refreshed tail.
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(define
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persist/view-peek
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(fn
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(b v)
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(persist/project-value
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(persist/snapshot-load b (get v :name) (get v :seed)))))
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; attach to a hub: refresh the view on every publish to its stream
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(define
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persist/view-attach
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(fn
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(h v)
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(begin
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(persist/subscribe
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h
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(persist/view-stream v)
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(fn (bk s e) (persist/view-refresh bk v)))
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h)))
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