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datalog: dl-magic-rewrite worklist now drains across rule chains (239/239)
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Real bug: the worklist used (set! queue (rest queue)) to pop the
head, which left queue bound to a fresh empty list as soon as the
last item was popped. Subsequent (append! queue ...) was a no-op
on the empty list — so when the head's rewrite generated new
(rel, adn) pairs to enqueue, they vanished. Multi-relation
programs (e.g. shortest -> path -> edge, or chained derived
relations) only had their head's rules rewritten; downstream
rules silently dropped.

Fix: use an index-based loop (idx 0 → len queue), with append!
adding to the same list. Items added after the current pointer
are picked up in subsequent iterations.

2 new regression tests:
- 4-level chain (a → r1 → r2 → r3 → r4) under magic returns 2
- shortest-path demo via magic equals dl-query (1 result)
This commit is contained in:
giles
2026-05-08 14:41:05 +00:00
parent e981368dcf
commit 17d6f58cc5
4 changed files with 53 additions and 26 deletions
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41
lib/datalog/magic.sx
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@@ -314,26 +314,27 @@
(dl-mq-mark! query-rel query-adornment)
(define
dl-mq-process
(fn
()
(when
(> (len queue) 0)
(let ((item (first queue)))
(do
(set! queue (rest queue))
(let
((rel (get item :rel)) (adn (get item :adn)))
(for-each
(fn
(rule)
(when
(= (dl-rel-name (get rule :head)) rel)
(dl-mq-rewrite-rule! rule adn)))
rules))
(dl-mq-process))))))
(dl-mq-process)
(let ((idx 0))
(define
dl-mq-process
(fn
()
(when
(< idx (len queue))
(let ((item (nth queue idx)))
(do
(set! idx (+ idx 1))
(let
((rel (get item :rel)) (adn (get item :adn)))
(for-each
(fn
(rule)
(when
(= (dl-rel-name (get rule :head)) rel)
(dl-mq-rewrite-rule! rule adn)))
rules))
(dl-mq-process))))))
(dl-mq-process))
{:rules out
:seed