Bug: dl-match-lit (the naive matcher used by dl-find-bindings)
was missing dl-aggregate? dispatch — it was only present in
dl-fbs-aux (semi-naive). Symptom:
(dl-query db '(count N X (p X)))
silently returned ().
Two fixes:
- Add aggregate branch to dl-match-lit before the positive case.
- dl-query-user-vars now projects only the result var (first arg)
of an aggregate goal — the aggregated var and inner-goal vars
are existentials and should not leak into substitutions.
2 new aggregate tests cover count and findall as direct query goals.
Bug: dl-check-stratifiable iterated body literals looking only for
explicit :neg literals, missing aggregate cycles. Now also walks
aggregates via dl-aggregate-dep-edge — q(N) :- count(N, X, q(X))
correctly errors out at saturation time.
3 new tests cover:
- recursion-through-aggregation rejected
- negation + aggregation coexist when in different strata
- min over empty derived relation produces no result
(findall L V Goal) — bind L to the distinct V values for which Goal
holds, or the empty list when none. One-line addition to
dl-do-aggregate that returns the unreduced list. Tests cover EDB,
derived relation, and empty cases.
Useful for "give me all the X such that ..." queries without
scalar reduction.
New lib/datalog/aggregates.sx: (count R V Goal), (sum R V Goal),
(min R V Goal), (max R V Goal). dl-eval-aggregate runs
dl-find-bindings on the goal under the outer subst, collects
distinct values of V, applies the operator, binds R. Empty input:
count/sum return 0; min/max produce no binding (rule fails).
Group-by emerges naturally from outer-subst substitution into the
goal — `popular(P) :- post(P), count(N, U, liked(U, P)), >=(N, 3).`
counts per-post.
Stratifier extended: dl-aggregate-dep-edge contributes a
negation-like edge so the aggregate's goal relation is fully
derived before the aggregate fires (non-monotonicity respected).
Safety relaxed for aggregates: goal-internal vars are existentials,
only the result var becomes bound.
