db gains :facts-index {<rel>: {<first-arg-key>: tuples}} mirroring
the membership :facts-keys index. dl-add-fact! populates the index;
dl-match-positive walks the body literal's first arg under the
current subst — when it's bound to a non-var, look up by (str arg)
instead of scanning the full relation.
For chain-style recursive rules (parent X Y), (ancestor Y Z) the
inner Y has at most one parent, so the inner lookup returns 0–1
tuples instead of N. chain-25 saturation drops from ~33s to ~18s
real (~2x). chain-50 still long but tractable; next bottleneck is
subst dict copies during unification.
dl-retract! refreshed to keep the new index consistent: kept-index
rebuilt during EDB filter, IDB wipes clear all three slots.
Differential semi-naive test bumped to chain-12, semi-only count
test to chain-25.
dl-find-bindings now uses dl-fb-aux lits db subst i n (indexed
iteration via nth) instead of recursive (rest lits). Eliminates
O(N²) list-copy per body of length N. chain-15 saturation 25s
→ 16s; chain-25 finishes in 33s real (vs. timeout previously).
Bumped semi_naive tests to chain-10 differential + chain-15
semi-only count (was chain-5/chain-5). Blocker entry refreshed.
dl-saturate! is now semi-naive: tracks a per-relation delta dict,
and on each iteration walks every positive body-literal position,
substituting the delta of its relation while joining the rest
against the previous-iteration DB. Candidates are collected before
mutating the DB so the "full" sides see a consistent snapshot.
Rules with no positive body literal (e.g. (p X) :- (= X 5).)
fall back to a one-shot naive pass via dl-collect-rule-candidates.
dl-saturate-naive! retained as the reference implementation; 8
differential tests compare per-relation tuple counts on every
recursive program. Switched dl-tuple-member? to indexed iteration
instead of recursive rest (eliminates per-step list copy). Larger
chains under bundled conformance trip O(n) membership × CPU
sharing — added a Blocker to swap relations to hash-set membership.
