datalog: disjunction via multiple rules test (231/231)

lib/datalog/tests/eval.sx

@@ -273,6 +273,19 @@
           (dl-saturated? db))
         false)
 
+      ;; Disjunction via multiple rules — Datalog has no `;` in
+      ;; body, so disjunction is expressed as separate rules with
+      ;; the same head. Here plant_based(X) is satisfied by either
+      ;; vegan(X) or vegetarian(X).
+      (dl-et-test-set! "disjunction via multiple rules"
+        (dl-query
+          (dl-program
+            "vegan(alice). vegetarian(bob). meat_eater(carol).
+             plant_based(X) :- vegan(X).
+             plant_based(X) :- vegetarian(X).")
+          (list (quote plant_based) (quote X)))
+        (list {:X (quote alice)} {:X (quote bob)}))
+
       ;; Bipartite-style join: pair-of-friends who share a hobby.
       ;; Three-relation join exercising the planner's join order.
       (dl-et-test-set! "bipartite friends-with-hobby"