datalog: dl-eval ≡ dl-eval-magic equivalence test (215/215)

lib/datalog/tests/api.sx

@@ -261,6 +261,20 @@
           "?- ancestor(a, X).")
         (list {:X (quote b)} {:X (quote c)}))
 
+      ;; Equivalence: dl-eval and dl-eval-magic produce the same
+      ;; answers for any well-formed query (magic-sets is a perf
+      ;; alternative, not a semantic change).
+      (dl-api-test! "dl-eval ≡ dl-eval-magic on ancestor"
+        (let
+          ((source "parent(a, b). parent(b, c). parent(c, d).
+                    ancestor(X, Y) :- parent(X, Y).
+                    ancestor(X, Z) :- parent(X, Y), ancestor(Y, Z)."))
+          (let
+            ((semi (dl-eval source "?- ancestor(a, X)."))
+              (magic (dl-eval-magic source "?- ancestor(a, X).")))
+            (= (len semi) (len magic))))
+        true)
+
       ;; Comprehensive integration: recursion + stratified negation
       ;; + aggregation + comparison composed in a single program.
       ;; (Uses _Anything as a regular var instead of `_` so the