datalog: dl-summary inspection helper (173/173)

Returns {<rel-name>: tuple-count} for relations with any tuples
or that are rule-headed (so empty IDB shows as :rel 0 rather than
disappearing). Skips placeholder entries from internal
dl-ensure-rel! calls. 4 tests cover basic, empty IDB, mixed
EDB+IDB, and empty-db cases.

lib/datalog/db.sx

@@ -327,3 +327,40 @@
           (fn (k) (set! total (+ total (len (get facts k)))))
           (keys facts))
         total))))
+
+;; Returns {<rel-name>: tuple-count} for debugging. Includes
+;; relations with any tuples plus all rule-head relations (so empty
+;; IDB shows as 0). Skips empty EDB-only entries that are placeholders
+;; from internal `dl-ensure-rel!` calls.
+(define
+  dl-summary
+  (fn
+    (db)
+    (let
+      ((facts (get db :facts))
+        (out {})
+        (rule-heads (list)))
+      (do
+        (for-each
+          (fn
+            (rule)
+            (let ((h (dl-rel-name (get rule :head))))
+              (when
+                (and (not (nil? h)) (not (dl-member-string? h rule-heads)))
+                (append! rule-heads h))))
+          (dl-rules db))
+        (for-each
+          (fn
+            (k)
+            (let ((c (len (get facts k))))
+              (when
+                (or (> c 0) (dl-member-string? k rule-heads))
+                (dict-set! out k c))))
+          (keys facts))
+        ;; Add rule heads that have no facts (yet).
+        (for-each
+          (fn
+            (k)
+            (when (not (has-key? out k)) (dict-set! out k 0)))
+          rule-heads)
+        out))))

lib/datalog/scoreboard.json

@@ -1,13 +1,13 @@
 {
   "lang": "datalog",
-  "total_passed": 169,
+  "total_passed": 173,
   "total_failed": 0,
-  "total": 169,
+  "total": 173,
   "suites": [
     {"name":"tokenize","passed":26,"failed":0,"total":26},
     {"name":"parse","passed":18,"failed":0,"total":18},
     {"name":"unify","passed":28,"failed":0,"total":28},
-    {"name":"eval","passed":18,"failed":0,"total":18},
+    {"name":"eval","passed":22,"failed":0,"total":22},
     {"name":"builtins","passed":19,"failed":0,"total":19},
     {"name":"semi_naive","passed":8,"failed":0,"total":8},
     {"name":"negation","passed":10,"failed":0,"total":10},
@@ -15,5 +15,5 @@
     {"name":"api","passed":11,"failed":0,"total":11},
     {"name":"demo","passed":15,"failed":0,"total":15}
   ],
-  "generated": "2026-05-08T09:27:29+00:00"
+  "generated": "2026-05-08T09:30:37+00:00"
 }

lib/datalog/scoreboard.md

@@ -1,13 +1,13 @@
 # datalog scoreboard
 
-**169 / 169 passing** (0 failure(s)).
+**173 / 173 passing** (0 failure(s)).
 
 | Suite | Passed | Total | Status |
 |-------|--------|-------|--------|
 | tokenize | 26 | 26 | ok |
 | parse | 18 | 18 | ok |
 | unify | 28 | 28 | ok |
-| eval | 18 | 18 | ok |
+| eval | 22 | 22 | ok |
 | builtins | 19 | 19 | ok |
 | semi_naive | 8 | 8 | ok |
 | negation | 10 | 10 | ok |

lib/datalog/tests/eval.sx

@@ -215,7 +215,36 @@
         (dl-query
           (dl-program "p(1, 2, 3). p(4, 5, 6).")
           (list (quote p) (quote _) (quote X) (quote _)))
-        (list {:X 2} {:X 5})))))
+        (list {:X 2} {:X 5}))
+
+      ;; dl-summary: relation -> tuple-count for inspection.
+      (dl-et-test! "dl-summary basic"
+        (dl-summary
+          (let
+            ((db (dl-program "p(1). p(2). q(3).")))
+            (do (dl-saturate! db) db)))
+        {:p 2 :q 1})
+
+      (dl-et-test! "dl-summary empty IDB shown"
+        (dl-summary
+          (let
+            ((db (dl-program "r(X) :- s(X).")))
+            (do (dl-saturate! db) db)))
+        {:r 0})
+
+      (dl-et-test! "dl-summary mixed EDB and IDB"
+        (dl-summary
+          (let
+            ((db (dl-program
+                   "parent(a, b).
+                    ancestor(X, Y) :- parent(X, Y).
+                    ancestor(X, Z) :- parent(X, Y), ancestor(Y, Z).")))
+            (do (dl-saturate! db) db)))
+        {:parent 1 :ancestor 1})
+
+      (dl-et-test! "dl-summary empty db"
+        (dl-summary (dl-make-db))
+        {}))))
 
 (define
   dl-eval-tests-run!