datalog: magic preserves arithmetic test (221/221)

lib/datalog/tests/magic.sx

@@ -256,6 +256,18 @@
                 (and (= semi-count 78) (= magic-count 12))))))
         true)
 
+      ;; Magic + arithmetic: rules with `is` clauses pass through
+      ;; the rewriter unchanged (built-ins aren't propagated).
+      (dl-mt-test! "magic preserves arithmetic"
+        (let
+          ((source "n(1). n(2). n(3).
+                    doubled(X, Y) :- n(X), is(Y, *(X, 2))."))
+          (let
+            ((semi (dl-eval source "?- doubled(2, Y)."))
+              (magic (dl-eval-magic source "?- doubled(2, Y).")))
+            (= (len semi) (len magic))))
+        true)
+
       (dl-mt-test! "magic skips irrelevant clusters"
         (let
           ;; Two disjoint chains. Query is rooted in cluster 1.