Two disjoint chains, query rooted in cluster 1. Semi-naive
derives the full closure over both clusters (6 ancestor tuples).
Magic-sets only seeds magic_ancestor^bf for cluster 1, so only
2 query-relevant tuples are returned (a→b, a→c). The test
asserts both numbers, demonstrating the actual perf-shape
benefit of goal-directed evaluation.
End-to-end magic-sets entry point. Given (db, query-goal):
- copies the caller's EDB facts (relations not headed by any
rule) into a fresh internal db
- adds the magic seed fact
- adds the rewritten rules
- saturates and runs the query
- returns the substitution list
Caller's db is untouched. Equivalent to dl-query for any
fully-stratifiable program; intended as a perf alternative on
goal-shaped queries against large recursive relations.
2 new tests: equivalence to dl-query on chain-3 ancestor, and
non-mutation of the caller's db (rules count unchanged).
dl-magic-rewrite rules query-rel adn args returns:
{:rules <rewritten-rules> :seed <magic-seed-fact>}
Worklist over (rel, adn) pairs starts from the query and stops
when no new pairs appear. For each rule with head matching a
worklist pair:
- Adorned rule: head :- magic_<rel>^<adn>(bound), body...
- Propagation rules: for each positive non-builtin body lit
at position i:
magic_<lit-rel>^<lit-adn>(bound-of-lit) :-
magic_<rel>^<adn>(bound-of-head),
body[0..i-1]
- Add (lit-rel, lit-adn) to the worklist.
Built-ins, negation, and aggregates pass through without
generating propagation rules. EDB facts are unchanged.
3 new tests cover seed structure, equivalence on chain-3 (full
closure, 6 ancestor tuples — magic helps only when the EDB has
nodes outside the seed's transitive cone), and same-query-answers
under the rewritten program. Total 202/202.
Wiring up a `dl-saturate-magic!` driver and large-graph perf
benchmarks is left for a future iteration.
Adds the primitives a future magic-sets rewriter will compose:
dl-magic-rel-name rel adornment → "magic_<rel>^<adornment>"
dl-magic-lit rel adn bound-args → magic literal as SX list
dl-bound-args lit adornment → bound-position arg values
Rewriter algorithm (worklist over (rel, adornment) pairs,
generating seed, propagation, and adorned-rule outputs) is still
TODO — these helpers are inspection-only for now.
4 new magic tests cover naming, lit construction, and bound-args
extraction (mixed/free).
New lib/datalog/magic.sx — first piece of magic-sets:
dl-adorn-arg arg bound → "b" or "f"
dl-adorn-args args bound → adornment string
dl-adorn-goal goal → adornment under empty bound set
dl-adorn-lit lit bound → adornment of any literal
dl-vars-bound-by-lit lit bound → free vars this lit will bind
dl-init-head-bound head adn → bound set seeded from head adornment
dl-rule-sips rule head-adn → ({:lit :adornment} ...) per body lit
SIPS walks left-to-right tracking the bound set; recognises `is` and
aggregate result-vars as new binders, lets comparisons and negation
pass through with computed adornments.
Inspection-only — saturator doesn't yet consume these. Lays
groundwork for a future magic-sets transformation.
10 new tests cover pure adornment, SIPS over a chain rule,
head-fully-bound rules, comparisons, and `is`. Total 194/194.
