datalog: magic-sets building blocks (199/199)

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).

lib/datalog/magic.sx

@@ -158,3 +158,45 @@
                       (dl-vars-bound-by-lit lit bound)))))))
           (get rule :body))
         out))))
+
+;; ── Magic predicate naming + bound-args extraction ─────────────
+;; These are building blocks for the magic-sets *transformation*
+;; itself. The transformation (which generates rewritten rules
+;; with magic_<rel>^<adornment> filters) is future work — for now
+;; these helpers can be used to inspect what such a transformation
+;; would produce.
+
+;; "magic_p^bf" given relation "p" and adornment "bf".
+(define
+  dl-magic-rel-name
+  (fn (rel adornment) (str "magic_" rel "^" adornment)))
+
+;; A magic predicate literal:
+;;   (magic_<rel>^<adornment> arg1 arg2 ...)
+(define
+  dl-magic-lit
+  (fn
+    (rel adornment bound-args)
+    (cons (string->symbol (dl-magic-rel-name rel adornment)) bound-args)))
+
+;; Extract bound args (those at "b" positions in `adornment`) from a
+;; literal `(rel arg1 arg2 ... argN)`. Returns the list of arg values.
+(define
+  dl-bound-args
+  (fn
+    (lit adornment)
+    (let ((args (rest lit)) (out (list)))
+      (do
+        (define
+          dl-ba-loop
+          (fn
+            (i)
+            (when
+              (< i (len args))
+              (do
+                (when
+                  (= (slice adornment i (+ i 1)) "b")
+                  (append! out (nth args i)))
+                (dl-ba-loop (+ i 1))))))
+        (dl-ba-loop 0)
+        out))))

lib/datalog/scoreboard.json

@@ -1,8 +1,8 @@
 {
   "lang": "datalog",
-  "total_passed": 194,
+  "total_passed": 199,
   "total_failed": 0,
-  "total": 194,
+  "total": 199,
   "suites": [
     {"name":"tokenize","passed":26,"failed":0,"total":26},
     {"name":"parse","passed":18,"failed":0,"total":18},
@@ -13,8 +13,8 @@
     {"name":"negation","passed":10,"failed":0,"total":10},
     {"name":"aggregates","passed":18,"failed":0,"total":18},
     {"name":"api","passed":14,"failed":0,"total":14},
-    {"name":"magic","passed":10,"failed":0,"total":10},
+    {"name":"magic","passed":15,"failed":0,"total":15},
     {"name":"demo","passed":18,"failed":0,"total":18}
   ],
-  "generated": "2026-05-08T09:50:50+00:00"
+  "generated": "2026-05-08T09:53:23+00:00"
 }

lib/datalog/scoreboard.md

@@ -1,6 +1,6 @@
 # datalog scoreboard
 
-**194 / 194 passing** (0 failure(s)).
+**199 / 199 passing** (0 failure(s)).
 
 | Suite | Passed | Total | Status |
 |-------|--------|-------|--------|
@@ -13,5 +13,5 @@
 | negation | 10 | 10 | ok |
 | aggregates | 18 | 18 | ok |
 | api | 14 | 14 | ok |
-| magic | 10 | 10 | ok |
+| magic | 15 | 15 | ok |
 | demo | 18 | 18 | ok |

lib/datalog/tests/magic.sx

@@ -124,7 +124,30 @@
           {:lit (list (quote p) (quote X)) :adornment "f"}
           {:lit (list (quote is) (quote Y)
                       (list (string->symbol "+") (quote X) 1))
-           :adornment "fb"})))))
+           :adornment "fb"}))
+
+      ;; Magic predicate naming.
+      (dl-mt-test! "magic-rel-name"
+        (dl-magic-rel-name "ancestor" "bf")
+        "magic_ancestor^bf")
+
+      ;; Bound-args extraction.
+      (dl-mt-test! "bound-args bf"
+        (dl-bound-args (list (quote ancestor) (quote tom) (quote X)) "bf")
+        (list (quote tom)))
+
+      (dl-mt-test! "bound-args mixed"
+        (dl-bound-args (list (quote p) 1 (quote Y) 3) "bfb")
+        (list 1 3))
+
+      (dl-mt-test! "bound-args all-free"
+        (dl-bound-args (list (quote p) (quote X) (quote Y)) "ff")
+        (list))
+
+      ;; Magic literal construction.
+      (dl-mt-test! "magic-lit"
+        (dl-magic-lit "ancestor" "bf" (list (quote tom)))
+        (list (string->symbol "magic_ancestor^bf") (quote tom))))))
 
 (define
   dl-magic-tests-run!

plans/datalog-on-sx.md

@@ -156,6 +156,8 @@ large graphs.
       is a constant or a variable already in the bound set.
 - [ ] Magic transformation: for each adorned predicate, generate a
       `magic_<pred>` relation and rewrite rule bodies to filter through it.
+      *Building blocks present in `magic.sx`: `dl-magic-rel-name`,
+      `dl-magic-lit`, `dl-bound-args`. Full rewriter still TODO.*
 - [x] Sideways information passing strategy (SIPS): left-to-right
       `dl-rule-sips rule head-adornment` walks body literals tracking
       the bound set, returning `({:lit :adornment} ...)`. Recognises
@@ -289,6 +291,12 @@ large graphs.
 
 _Newest first._
 
+- 2026-05-08 — Phase 6 building blocks for the magic-sets
+  transformation: `dl-magic-rel-name`, `dl-magic-lit`,
+  `dl-bound-args`. The rewriter that generates magic seed and
+  propagation rules is still future work; with these primitives
+  in place it's a straightforward worklist algorithm. 4 new tests.
+
 - 2026-05-08 — Phase 6 adornments + SIPS in
   `lib/datalog/magic.sx`. Inspection helpers — `dl-adorn-goal` and
   `dl-adorn-lit` compute per-arg `b`/`f` patterns under a bound