datalog: dl-clear-idb! helper (208/208)

Wipes every rule-headed relation (the IDB) — leaves EDB facts and
rule definitions intact. Useful for inspecting the EDB-only
baseline or for forcing a clean re-saturation.

  (dl-saturate! db)
  (dl-clear-idb! db)        ; ancestor relation now empty
  (dl-saturate! db)         ; re-derives ancestor from parents

2 new api tests verify IDB-wipe and EDB-preservation.

lib/datalog/api.sx

@@ -213,3 +213,23 @@
                 (append! seen h))))
           (dl-rules db))
         seen))))
+
+;; Wipe every relation that has at least one rule (i.e. every IDB
+;; relation) — leaves EDB facts and rule definitions intact. Useful
+;; before a follow-up `dl-saturate!` if you want a clean restart, or
+;; for inspection of the EDB-only baseline.
+(define
+  dl-clear-idb!
+  (fn
+    (db)
+    (let ((rule-heads (dl-rule-head-rels db)))
+      (do
+        (for-each
+          (fn
+            (k)
+            (do
+              (dict-set! (get db :facts) k (list))
+              (dict-set! (get db :facts-keys) k {})
+              (dict-set! (get db :facts-index) k {})))
+          rule-heads)
+        db))))

lib/datalog/scoreboard.json

@@ -1,8 +1,8 @@
 {
   "lang": "datalog",
-  "total_passed": 206,
+  "total_passed": 208,
   "total_failed": 0,
-  "total": 206,
+  "total": 208,
   "suites": [
     {"name":"tokenize","passed":26,"failed":0,"total":26},
     {"name":"parse","passed":18,"failed":0,"total":18},
@@ -12,9 +12,9 @@
     {"name":"semi_naive","passed":8,"failed":0,"total":8},
     {"name":"negation","passed":10,"failed":0,"total":10},
     {"name":"aggregates","passed":18,"failed":0,"total":18},
-    {"name":"api","passed":15,"failed":0,"total":15},
+    {"name":"api","passed":17,"failed":0,"total":17},
     {"name":"magic","passed":21,"failed":0,"total":21},
     {"name":"demo","passed":18,"failed":0,"total":18}
   ],
-  "generated": "2026-05-08T10:04:46+00:00"
+  "generated": "2026-05-08T10:06:36+00:00"
 }

lib/datalog/scoreboard.md

@@ -1,6 +1,6 @@
 # datalog scoreboard
 
-**206 / 206 passing** (0 failure(s)).
+**208 / 208 passing** (0 failure(s)).
 
 | Suite | Passed | Total | Status |
 |-------|--------|-------|--------|
@@ -12,6 +12,6 @@
 | semi_naive | 8 | 8 | ok |
 | negation | 10 | 10 | ok |
 | aggregates | 18 | 18 | ok |
-| api | 15 | 15 | ok |
+| api | 17 | 17 | ok |
 | magic | 21 | 21 | ok |
 | demo | 18 | 18 | ok |

lib/datalog/tests/api.sx

@@ -213,6 +213,30 @@
           "?- p(X), q(X).")
         (list {:X 2} {:X 3}))
 
+      ;; dl-clear-idb!: wipe rule-headed relations.
+      (dl-api-test! "dl-clear-idb! wipes IDB"
+        (let
+          ((db (dl-program
+                 "parent(a, b). parent(b, c).
+                  ancestor(X, Y) :- parent(X, Y).
+                  ancestor(X, Z) :- parent(X, Y), ancestor(Y, Z).")))
+          (do
+            (dl-saturate! db)
+            (dl-clear-idb! db)
+            (len (dl-relation db "ancestor"))))
+        0)
+
+      (dl-api-test! "dl-clear-idb! preserves EDB"
+        (let
+          ((db (dl-program
+                 "parent(a, b). parent(b, c).
+                  ancestor(X, Y) :- parent(X, Y).")))
+          (do
+            (dl-saturate! db)
+            (dl-clear-idb! db)
+            (len (dl-relation db "parent"))))
+        2)
+
       ;; dl-eval-magic — routes single-goal queries through
       ;; magic-sets evaluation.
       (dl-api-test-set! "dl-eval-magic ancestor"