datalog: aggregates work as top-level query goals (183/183)

Bug: dl-match-lit (the naive matcher used by dl-find-bindings)
was missing dl-aggregate? dispatch — it was only present in
dl-fbs-aux (semi-naive). Symptom:
  (dl-query db '(count N X (p X)))
silently returned ().

Two fixes:
- Add aggregate branch to dl-match-lit before the positive case.
- dl-query-user-vars now projects only the result var (first arg)
  of an aggregate goal — the aggregated var and inner-goal vars
  are existentials and should not leak into substitutions.

2 new aggregate tests cover count and findall as direct query goals.

lib/datalog/eval.sx

@@ -83,6 +83,7 @@
     (cond
       ((and (dict? lit) (has-key? lit :neg))
         (dl-match-negation (get lit :neg) db subst))
+      ((dl-aggregate? lit) (dl-eval-aggregate lit db subst))
       ((dl-builtin? lit)
         (let
           ((s (dl-eval-builtin lit subst)))
@@ -426,16 +427,35 @@
         (for-each
           (fn
             (g)
-            (let
-              ((tgt
-                 (if (and (dict? g) (has-key? g :neg)) (get g :neg) g)))
-              (for-each
-                (fn
-                  (v)
+            (cond
+              ((and (dict? g) (has-key? g :neg))
+                (for-each
+                  (fn
+                    (v)
+                    (when
+                      (and (not (= v "_")) (not (dl-member-string? v seen)))
+                      (append! seen v)))
+                  (dl-vars-of (get g :neg))))
+              ((dl-aggregate? g)
+                ;; Only the result var (first arg of the aggregate
+                ;; literal) is user-facing. The aggregated var and
+                ;; any vars in the inner goal are internal.
+                (let ((r (nth g 1)))
                   (when
-                    (and (not (= v "_")) (not (dl-member-string? v seen)))
-                    (append! seen v)))
-                (dl-vars-of tgt))))
+                    (dl-var? r)
+                    (let ((rn (symbol->string r)))
+                      (when
+                        (and (not (= rn "_"))
+                             (not (dl-member-string? rn seen)))
+                        (append! seen rn))))))
+              (else
+                (for-each
+                  (fn
+                    (v)
+                    (when
+                      (and (not (= v "_")) (not (dl-member-string? v seen)))
+                      (append! seen v)))
+                  (dl-vars-of g)))))
           goals)
         seen))))
 

lib/datalog/scoreboard.json

@@ -1,8 +1,8 @@
 {
   "lang": "datalog",
-  "total_passed": 181,
+  "total_passed": 183,
   "total_failed": 0,
-  "total": 181,
+  "total": 183,
   "suites": [
     {"name":"tokenize","passed":26,"failed":0,"total":26},
     {"name":"parse","passed":18,"failed":0,"total":18},
@@ -11,9 +11,9 @@
     {"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},
-    {"name":"aggregates","passed":16,"failed":0,"total":16},
+    {"name":"aggregates","passed":18,"failed":0,"total":18},
     {"name":"api","passed":13,"failed":0,"total":13},
     {"name":"demo","passed":18,"failed":0,"total":18}
   ],
-  "generated": "2026-05-08T09:40:51+00:00"
+  "generated": "2026-05-08T09:45:03+00:00"
 }

lib/datalog/scoreboard.md

@@ -1,6 +1,6 @@
 # datalog scoreboard
 
-**181 / 181 passing** (0 failure(s)).
+**183 / 183 passing** (0 failure(s)).
 
 | Suite | Passed | Total | Status |
 |-------|--------|-------|--------|
@@ -11,6 +11,6 @@
 | builtins | 19 | 19 | ok |
 | semi_naive | 8 | 8 | ok |
 | negation | 10 | 10 | ok |
-| aggregates | 16 | 16 | ok |
+| aggregates | 18 | 18 | ok |
 | api | 13 | 13 | ok |
 | demo | 18 | 18 | ok |

lib/datalog/tests/aggregates.sx

@@ -260,6 +260,21 @@
           (list (quote low) (quote M)))
         (list))
 
+      ;; Aggregates as the top-level query goal (regression for
+      ;; dl-match-lit aggregate dispatch and projection cleanup).
+      (dl-at-test-set! "count as query goal"
+        (dl-query
+          (dl-program "p(1). p(2). p(3). p(4).")
+          (list (quote count) (quote N) (quote X) (list (quote p) (quote X))))
+        (list {:N 4}))
+
+      (dl-at-test-set! "findall as query goal"
+        (dl-query
+          (dl-program "p(1). p(2). p(3).")
+          (list (quote findall) (quote L) (quote X)
+                (list (quote p) (quote X))))
+        (list {:L (list 1 2 3)}))
+
       (dl-at-test-set! "distinct counted once"
         (dl-query
           (dl-program

plans/datalog-on-sx.md

@@ -284,6 +284,16 @@ large graphs.
 
 _Newest first._
 
+- 2026-05-08 — Bug fix: aggregates work as top-level query goals.
+  `dl-match-lit` (the naive matcher used by `dl-find-bindings`) was
+  missing the `dl-aggregate?` dispatch — it was only present in
+  `dl-fbs-aux` (semi-naive). Symptom: `(dl-query db '(count N X (p X)))`
+  silently returned `()`. Also updated `dl-query-user-vars` to project
+  only the result var (first arg) of an aggregate goal — the
+  aggregated var and inner-goal vars are existentials and should not
+  appear in the projected substitution. 2 new aggregate tests cover
+  the regression.
+
 - 2026-05-08 — Convenience: `dl-eval source query-source`. Parses
   both strings, builds a db, saturates, runs the query, returns
   the substitution list. Single-call user-friendly entry. 2 new