datalog: bounded-successor regression test (224/224)

lib/datalog/scoreboard.json

@@ -1,14 +1,14 @@
 {
   "lang": "datalog",
-  "total_passed": 223,
+  "total_passed": 224,
   "total_failed": 0,
-  "total": 223,
+  "total": 224,
   "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":30,"failed":0,"total":30},
-    {"name":"builtins","passed":19,"failed":0,"total":19},
+    {"name":"builtins","passed":20,"failed":0,"total":20},
     {"name":"semi_naive","passed":8,"failed":0,"total":8},
     {"name":"negation","passed":10,"failed":0,"total":10},
     {"name":"aggregates","passed":19,"failed":0,"total":19},
@@ -16,5 +16,5 @@
     {"name":"magic","passed":24,"failed":0,"total":24},
     {"name":"demo","passed":21,"failed":0,"total":21}
   ],
-  "generated": "2026-05-08T10:33:34+00:00"
+  "generated": "2026-05-08T10:36:02+00:00"
 }

lib/datalog/scoreboard.md

@@ -1,6 +1,6 @@
 # datalog scoreboard
 
-**223 / 223 passing** (0 failure(s)).
+**224 / 224 passing** (0 failure(s)).
 
 | Suite | Passed | Total | Status |
 |-------|--------|-------|--------|
@@ -8,7 +8,7 @@
 | parse | 18 | 18 | ok |
 | unify | 28 | 28 | ok |
 | eval | 30 | 30 | ok |
-| builtins | 19 | 19 | ok |
+| builtins | 20 | 20 | ok |
 | semi_naive | 8 | 8 | ok |
 | negation | 10 | 10 | ok |
 | aggregates | 19 | 19 | ok |

lib/datalog/tests/builtins.sx

@@ -179,6 +179,17 @@
           ((db (dl-program "n(0). n(1). n(2). n(3). n(4). n(5). n(6). n(7). n(8). n(9).\n                  big(X) :- n(X), >=(X, 5).")))
           (do (dl-saturate! db) (len (dl-relation db "big"))))
         5)
+      ;; Bounded successor: a recursive rule with a comparison
+      ;; guard terminates because the Herbrand base is effectively
+      ;; bounded.
+      (dl-bt-test-set! "bounded successor"
+        (dl-query
+          (dl-program
+            "nat(0).
+             nat(Y) :- nat(X), is(Y, +(X, 1)), <(Y, 5).")
+          (list (quote nat) (quote X)))
+        (list {:X 0} {:X 1} {:X 2} {:X 3} {:X 4}))
+
       (dl-bt-test!
         "unsafe — comparison without binder"
         (dl-bt-throws? (fn () (dl-program "p(X) :- <(X, 5).")))