datalog: dl-rules-of relation-inspection helper (214/214)

(dl-rules-of db rel-name) → list of rules with head matching
the given relation name. Useful for tooling and debugging
("show me how this relation is derived") without exposing the
internal :rules list directly.

2 new api tests cover hit and miss cases.

lib/datalog/api.sx

@@ -198,6 +198,24 @@
                 (dl-magic-query db (first qbody)))
               (else (dl-query db qbody)))))))))
 
+;; List rules whose head's relation matches `rel-name`. Useful for
+;; inspection ("show me how this relation is derived") without
+;; exposing the internal `:rules` list.
+(define
+  dl-rules-of
+  (fn
+    (db rel-name)
+    (let ((out (list)))
+      (do
+        (for-each
+          (fn
+            (rule)
+            (when
+              (= (dl-rel-name (get rule :head)) rel-name)
+              (append! out rule)))
+          (dl-rules db))
+        out))))
+
 (define
   dl-rule-head-rels
   (fn

lib/datalog/scoreboard.json

@@ -1,8 +1,8 @@
 {
   "lang": "datalog",
-  "total_passed": 212,
+  "total_passed": 214,
   "total_failed": 0,
-  "total": 212,
+  "total": 214,
   "suites": [
     {"name":"tokenize","passed":26,"failed":0,"total":26},
     {"name":"parse","passed":18,"failed":0,"total":18},
@@ -12,9 +12,9 @@
     {"name":"semi_naive","passed":8,"failed":0,"total":8},
     {"name":"negation","passed":10,"failed":0,"total":10},
     {"name":"aggregates","passed":18,"failed":0,"total":18},
-    {"name":"api","passed":17,"failed":0,"total":17},
+    {"name":"api","passed":19,"failed":0,"total":19},
     {"name":"magic","passed":22,"failed":0,"total":22},
     {"name":"demo","passed":18,"failed":0,"total":18}
   ],
-  "generated": "2026-05-08T10:15:09+00:00"
+  "generated": "2026-05-08T10:17:32+00:00"
 }

lib/datalog/scoreboard.md

@@ -1,6 +1,6 @@
 # datalog scoreboard
 
-**212 / 212 passing** (0 failure(s)).
+**214 / 214 passing** (0 failure(s)).
 
 | Suite | Passed | Total | Status |
 |-------|--------|-------|--------|
@@ -12,6 +12,6 @@
 | semi_naive | 8 | 8 | ok |
 | negation | 10 | 10 | ok |
 | aggregates | 18 | 18 | ok |
-| api | 17 | 17 | ok |
+| api | 19 | 19 | ok |
 | magic | 22 | 22 | ok |
 | demo | 18 | 18 | ok |

lib/datalog/tests/api.sx

@@ -213,6 +213,20 @@
           "?- p(X), q(X).")
         (list {:X 2} {:X 3}))
 
+      ;; dl-rules-of: rules with head matching a relation name.
+      (dl-api-test! "dl-rules-of count"
+        (let
+          ((db (dl-program
+                 "p(1). q(X) :- p(X). r(X) :- p(X). q(2).")))
+          (len (dl-rules-of db "q")))
+        1)
+
+      (dl-api-test! "dl-rules-of empty"
+        (let
+          ((db (dl-program "p(1). p(2).")))
+          (len (dl-rules-of db "q")))
+        0)
+
       ;; dl-clear-idb!: wipe rule-headed relations.
       (dl-api-test! "dl-clear-idb! wipes IDB"
         (let