Set predicates: foldl/4, list_to_set/2, intersection/3, subtract/3, union/3

Adds 5 new built-in predicates to the Prolog runtime with 15 tests.
390 → 405 tests across 20 suites (all passing).

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

lib/prolog/conformance.sh

@@ -35,6 +35,7 @@ SUITES=(
   "meta_predicates:lib/prolog/tests/meta_predicates.sx:pl-meta-predicates-tests-run!"
   "list_predicates:lib/prolog/tests/list_predicates.sx:pl-list-predicates-tests-run!"
   "meta_call:lib/prolog/tests/meta_call.sx:pl-meta-call-tests-run!"
+  "set_predicates:lib/prolog/tests/set_predicates.sx:pl-set-predicates-tests-run!"
 )
 
 SCRIPT='(epoch 1)

lib/prolog/runtime.sx

@@ -1169,6 +1169,50 @@
                         false))))))))
         (else false)))))
 
+(define
+  pl-solve-foldl!
+  (fn
+    (db goal lst vin vout trail k)
+    (let
+      ((l (pl-walk-deep lst)) (v0 (pl-walk vin)))
+      (cond
+        ((and (pl-atom? l) (= (pl-atom-name l) "[]"))
+          (if (pl-unify! vout v0 trail) (k) false))
+        ((and (pl-compound? l) (= (pl-fun l) "."))
+          (let
+            ((head (first (pl-args l))) (tail (nth (pl-args l) 1)))
+            (let
+              ((v1-var (pl-mk-rt-var "_FV")))
+              (let
+                ((call-goal (pl-apply-goal goal (list head v0 v1-var))))
+                (if
+                  (pl-solve-once! db call-goal trail)
+                  (pl-solve-foldl! db goal tail v1-var vout trail k)
+                  false)))))
+        (else false)))))
+
+(define
+  pl-list-to-set-sx
+  (fn
+    (lst seen)
+    (if
+      (empty? lst)
+      (list)
+      (let
+        ((head (first lst)) (tail (rest lst)))
+        (if
+          (some (fn (s) (pl-struct-eq? head s)) seen)
+          (pl-list-to-set-sx tail seen)
+          (cons head (pl-list-to-set-sx tail (cons head seen))))))))
+
+(define
+  pl-pl-list-contains?
+  (fn
+    (pl-lst elem)
+    (let
+      ((sx-lst (pl-prolog-list-to-sx (pl-walk-deep pl-lst))))
+      (some (fn (x) (pl-struct-eq? elem x)) sx-lst))))
+
 (define
   pl-solve!
   (fn
@@ -1758,6 +1802,84 @@
             ((cond-g (pl-walk (first (pl-args g))))
               (action-g (pl-walk (nth (pl-args g) 1))))
             (pl-solve-forall! db cond-g action-g trail cut-box k)))
+        ((and (pl-compound? g) (= (pl-fun g) "foldl") (= (len (pl-args g)) 4))
+          (pl-solve-foldl!
+            db
+            (pl-walk (first (pl-args g)))
+            (pl-walk (nth (pl-args g) 1))
+            (pl-walk (nth (pl-args g) 2))
+            (pl-walk (nth (pl-args g) 3))
+            trail
+            k))
+        ((and (pl-compound? g) (= (pl-fun g) "list_to_set") (= (len (pl-args g)) 2))
+          (let
+            ((lst-rt (pl-walk (first (pl-args g))))
+              (res-rt (pl-walk (nth (pl-args g) 1))))
+            (if
+              (pl-proper-list? lst-rt)
+              (let
+                ((sx-lst (map (fn (x) (pl-walk-deep x)) (pl-prolog-list-to-sx lst-rt))))
+                (let
+                  ((unique-lst (pl-list-to-set-sx sx-lst (list))))
+                  (pl-solve-eq! res-rt (pl-list-to-prolog unique-lst) trail k)))
+              false)))
+        ((and (pl-compound? g) (= (pl-fun g) "intersection") (= (len (pl-args g)) 3))
+          (let
+            ((s1-rt (pl-walk (first (pl-args g))))
+              (s2-rt (pl-walk (nth (pl-args g) 1)))
+              (res-rt (pl-walk (nth (pl-args g) 2))))
+            (if
+              (and (pl-proper-list? s1-rt) (pl-proper-list? s2-rt))
+              (let
+                ((s1-sx (map (fn (x) (pl-walk-deep x)) (pl-prolog-list-to-sx s1-rt)))
+                  (s2-sx
+                    (map
+                      (fn (x) (pl-walk-deep x))
+                      (pl-prolog-list-to-sx s2-rt))))
+                (let
+                  ((inter (filter (fn (x) (some (fn (y) (pl-struct-eq? x y)) s2-sx)) s1-sx)))
+                  (pl-solve-eq! res-rt (pl-list-to-prolog inter) trail k)))
+              false)))
+        ((and (pl-compound? g) (= (pl-fun g) "subtract") (= (len (pl-args g)) 3))
+          (let
+            ((s1-rt (pl-walk (first (pl-args g))))
+              (s2-rt (pl-walk (nth (pl-args g) 1)))
+              (res-rt (pl-walk (nth (pl-args g) 2))))
+            (if
+              (and (pl-proper-list? s1-rt) (pl-proper-list? s2-rt))
+              (let
+                ((s1-sx (map (fn (x) (pl-walk-deep x)) (pl-prolog-list-to-sx s1-rt)))
+                  (s2-sx
+                    (map
+                      (fn (x) (pl-walk-deep x))
+                      (pl-prolog-list-to-sx s2-rt))))
+                (let
+                  ((diff (filter (fn (x) (not (some (fn (y) (pl-struct-eq? x y)) s2-sx))) s1-sx)))
+                  (pl-solve-eq! res-rt (pl-list-to-prolog diff) trail k)))
+              false)))
+        ((and (pl-compound? g) (= (pl-fun g) "union") (= (len (pl-args g)) 3))
+          (let
+            ((s1-rt (pl-walk (first (pl-args g))))
+              (s2-rt (pl-walk (nth (pl-args g) 1)))
+              (res-rt (pl-walk (nth (pl-args g) 2))))
+            (if
+              (and (pl-proper-list? s1-rt) (pl-proper-list? s2-rt))
+              (let
+                ((s1-sx (map (fn (x) (pl-walk-deep x)) (pl-prolog-list-to-sx s1-rt)))
+                  (s2-sx
+                    (map
+                      (fn (x) (pl-walk-deep x))
+                      (pl-prolog-list-to-sx s2-rt))))
+                (let
+                  ((s2-only (filter (fn (x) (not (some (fn (y) (pl-struct-eq? x y)) s1-sx))) s2-sx)))
+                  (let
+                    ((union-lst (append s1-sx s2-only)))
+                    (pl-solve-eq!
+                      res-rt
+                      (pl-list-to-prolog union-lst)
+                      trail
+                      k))))
+              false)))
         (true (pl-solve-user! db g trail cut-box k))))))
 
 (define

lib/prolog/scoreboard.json

@@ -1,7 +1,7 @@
 {
-  "total_passed": 390,
+  "total_passed": 405,
   "total_failed": 0,
-  "total": 390,
+  "total": 405,
-  "suites": {"parse":{"passed":25,"total":25,"failed":0},"unify":{"passed":47,"total":47,"failed":0},"clausedb":{"passed":14,"total":14,"failed":0},"solve":{"passed":62,"total":62,"failed":0},"operators":{"passed":19,"total":19,"failed":0},"dynamic":{"passed":11,"total":11,"failed":0},"findall":{"passed":11,"total":11,"failed":0},"term_inspect":{"passed":14,"total":14,"failed":0},"append":{"passed":6,"total":6,"failed":0},"reverse":{"passed":6,"total":6,"failed":0},"member":{"passed":7,"total":7,"failed":0},"nqueens":{"passed":6,"total":6,"failed":0},"family":{"passed":10,"total":10,"failed":0},"atoms":{"passed":34,"total":34,"failed":0},"query_api":{"passed":16,"total":16,"failed":0},"iso_predicates":{"passed":29,"total":29,"failed":0},"meta_predicates":{"passed":25,"total":25,"failed":0},"list_predicates":{"passed":33,"total":33,"failed":0},"meta_call":{"passed":15,"total":15,"failed":0}},
+  "suites": {"parse":{"passed":25,"total":25,"failed":0},"unify":{"passed":47,"total":47,"failed":0},"clausedb":{"passed":14,"total":14,"failed":0},"solve":{"passed":62,"total":62,"failed":0},"operators":{"passed":19,"total":19,"failed":0},"dynamic":{"passed":11,"total":11,"failed":0},"findall":{"passed":11,"total":11,"failed":0},"term_inspect":{"passed":14,"total":14,"failed":0},"append":{"passed":6,"total":6,"failed":0},"reverse":{"passed":6,"total":6,"failed":0},"member":{"passed":7,"total":7,"failed":0},"nqueens":{"passed":6,"total":6,"failed":0},"family":{"passed":10,"total":10,"failed":0},"atoms":{"passed":34,"total":34,"failed":0},"query_api":{"passed":16,"total":16,"failed":0},"iso_predicates":{"passed":29,"total":29,"failed":0},"meta_predicates":{"passed":25,"total":25,"failed":0},"list_predicates":{"passed":33,"total":33,"failed":0},"meta_call":{"passed":15,"total":15,"failed":0},"set_predicates":{"passed":15,"total":15,"failed":0}},
-  "generated": "2026-04-25T11:59:16+00:00"
+  "generated": "2026-04-25T12:21:38+00:00"
 }

lib/prolog/scoreboard.md

@@ -1,7 +1,7 @@
 # Prolog scoreboard
 
-**390 / 390 passing** (0 failure(s)).
+**405 / 405 passing** (0 failure(s)).
-Generated 2026-04-25T11:59:16+00:00.
+Generated 2026-04-25T12:21:38+00:00.
 
 | Suite | Passed | Total | Status |
 |-------|--------|-------|--------|
@@ -24,6 +24,7 @@ Generated 2026-04-25T11:59:16+00:00.
 | meta_predicates | 25 | 25 | ok |
 | list_predicates | 33 | 33 | ok |
 | meta_call | 15 | 15 | ok |
+| set_predicates | 15 | 15 | ok |
 
 Run `bash lib/prolog/conformance.sh` to refresh. Override the binary
 with `SX_SERVER=path/to/sx_server.exe bash …`.

lib/prolog/tests/set_predicates.sx

@@ -0,0 +1,195 @@
+;; lib/prolog/tests/set_predicates.sx — foldl/4, list_to_set/2, intersection/3, subtract/3, union/3
+
+(define pl-sp-test-count 0)
+(define pl-sp-test-pass 0)
+(define pl-sp-test-fail 0)
+(define pl-sp-test-failures (list))
+
+(define
+  pl-sp-test!
+  (fn
+    (name got expected)
+    (begin
+      (set! pl-sp-test-count (+ pl-sp-test-count 1))
+      (if
+        (= got expected)
+        (set! pl-sp-test-pass (+ pl-sp-test-pass 1))
+        (begin
+          (set! pl-sp-test-fail (+ pl-sp-test-fail 1))
+          (append!
+            pl-sp-test-failures
+            (str name "\n    expected: " expected "\n    got:      " got)))))))
+
+(define
+  pl-sp-goal
+  (fn
+    (src env)
+    (pl-instantiate (nth (first (pl-parse (str "g :- " src "."))) 2) env)))
+
+;; DB with add/3 for foldl tests
+(define pl-sp-db (pl-mk-db))
+(pl-db-load! pl-sp-db (pl-parse "add(X, Acc, NAcc) :- NAcc is Acc + X."))
+
+;; ── foldl/4 ────────────────────────────────────────────────────────
+
+(define pl-sp-env-fl1 {:S (pl-mk-rt-var "S")})
+(pl-solve-once!
+  pl-sp-db
+  (pl-sp-goal "foldl(add, [1,2,3,4], 0, S)" pl-sp-env-fl1)
+  (pl-mk-trail))
+(pl-sp-test!
+  "foldl(add,[1,2,3,4],0,S) -> S=10"
+  (pl-num-val (pl-walk-deep (dict-get pl-sp-env-fl1 "S")))
+  10)
+
+(define pl-sp-env-fl2 {:S (pl-mk-rt-var "S")})
+(pl-solve-once!
+  pl-sp-db
+  (pl-sp-goal "foldl(add, [], 5, S)" pl-sp-env-fl2)
+  (pl-mk-trail))
+(pl-sp-test!
+  "foldl(add,[],5,S) -> S=5"
+  (pl-num-val (pl-walk-deep (dict-get pl-sp-env-fl2 "S")))
+  5)
+
+(define pl-sp-env-fl3 {:S (pl-mk-rt-var "S")})
+(pl-solve-once!
+  pl-sp-db
+  (pl-sp-goal "foldl(add, [1,2,3], 0, S)" pl-sp-env-fl3)
+  (pl-mk-trail))
+(pl-sp-test!
+  "foldl(add,[1,2,3],0,S) -> S=6"
+  (pl-num-val (pl-walk-deep (dict-get pl-sp-env-fl3 "S")))
+  6)
+
+;; ── list_to_set/2 ──────────────────────────────────────────────────
+
+(define pl-sp-env-lts1 {:R (pl-mk-rt-var "R")})
+(pl-solve-once!
+  pl-sp-db
+  (pl-sp-goal "list_to_set([1,2,3,2,1], R)" pl-sp-env-lts1)
+  (pl-mk-trail))
+(pl-sp-test!
+  "list_to_set([1,2,3,2,1],R) -> [1,2,3]"
+  (pl-format-term (pl-walk-deep (dict-get pl-sp-env-lts1 "R")))
+  ".(1, .(2, .(3, [])))")
+
+(define pl-sp-env-lts2 {:R (pl-mk-rt-var "R")})
+(pl-solve-once!
+  pl-sp-db
+  (pl-sp-goal "list_to_set([], R)" pl-sp-env-lts2)
+  (pl-mk-trail))
+(pl-sp-test!
+  "list_to_set([],R) -> []"
+  (pl-format-term (pl-walk-deep (dict-get pl-sp-env-lts2 "R")))
+  "[]")
+
+(define pl-sp-env-lts3 {:R (pl-mk-rt-var "R")})
+(pl-solve-once!
+  pl-sp-db
+  (pl-sp-goal "list_to_set([a,b,a,c], R)" pl-sp-env-lts3)
+  (pl-mk-trail))
+(pl-sp-test!
+  "list_to_set([a,b,a,c],R) -> [a,b,c]"
+  (pl-format-term (pl-walk-deep (dict-get pl-sp-env-lts3 "R")))
+  ".(a, .(b, .(c, [])))")
+
+;; ── intersection/3 ─────────────────────────────────────────────────
+
+(define pl-sp-env-int1 {:R (pl-mk-rt-var "R")})
+(pl-solve-once!
+  pl-sp-db
+  (pl-sp-goal "intersection([1,2,3,4], [2,4,6], R)" pl-sp-env-int1)
+  (pl-mk-trail))
+(pl-sp-test!
+  "intersection([1,2,3,4],[2,4,6],R) -> [2,4]"
+  (pl-format-term (pl-walk-deep (dict-get pl-sp-env-int1 "R")))
+  ".(2, .(4, []))")
+
+(define pl-sp-env-int2 {:R (pl-mk-rt-var "R")})
+(pl-solve-once!
+  pl-sp-db
+  (pl-sp-goal "intersection([1,2,3], [4,5,6], R)" pl-sp-env-int2)
+  (pl-mk-trail))
+(pl-sp-test!
+  "intersection([1,2,3],[4,5,6],R) -> []"
+  (pl-format-term (pl-walk-deep (dict-get pl-sp-env-int2 "R")))
+  "[]")
+
+(define pl-sp-env-int3 {:R (pl-mk-rt-var "R")})
+(pl-solve-once!
+  pl-sp-db
+  (pl-sp-goal "intersection([], [1,2,3], R)" pl-sp-env-int3)
+  (pl-mk-trail))
+(pl-sp-test!
+  "intersection([],[1,2,3],R) -> []"
+  (pl-format-term (pl-walk-deep (dict-get pl-sp-env-int3 "R")))
+  "[]")
+
+;; ── subtract/3 ─────────────────────────────────────────────────────
+
+(define pl-sp-env-sub1 {:R (pl-mk-rt-var "R")})
+(pl-solve-once!
+  pl-sp-db
+  (pl-sp-goal "subtract([1,2,3,4], [2,4], R)" pl-sp-env-sub1)
+  (pl-mk-trail))
+(pl-sp-test!
+  "subtract([1,2,3,4],[2,4],R) -> [1,3]"
+  (pl-format-term (pl-walk-deep (dict-get pl-sp-env-sub1 "R")))
+  ".(1, .(3, []))")
+
+(define pl-sp-env-sub2 {:R (pl-mk-rt-var "R")})
+(pl-solve-once!
+  pl-sp-db
+  (pl-sp-goal "subtract([1,2,3], [], R)" pl-sp-env-sub2)
+  (pl-mk-trail))
+(pl-sp-test!
+  "subtract([1,2,3],[],R) -> [1,2,3]"
+  (pl-format-term (pl-walk-deep (dict-get pl-sp-env-sub2 "R")))
+  ".(1, .(2, .(3, [])))")
+
+(define pl-sp-env-sub3 {:R (pl-mk-rt-var "R")})
+(pl-solve-once!
+  pl-sp-db
+  (pl-sp-goal "subtract([], [1,2], R)" pl-sp-env-sub3)
+  (pl-mk-trail))
+(pl-sp-test!
+  "subtract([],[1,2],R) -> []"
+  (pl-format-term (pl-walk-deep (dict-get pl-sp-env-sub3 "R")))
+  "[]")
+
+;; ── union/3 ────────────────────────────────────────────────────────
+
+(define pl-sp-env-uni1 {:R (pl-mk-rt-var "R")})
+(pl-solve-once!
+  pl-sp-db
+  (pl-sp-goal "union([1,2,3], [2,3,4], R)" pl-sp-env-uni1)
+  (pl-mk-trail))
+(pl-sp-test!
+  "union([1,2,3],[2,3,4],R) -> [1,2,3,4]"
+  (pl-format-term (pl-walk-deep (dict-get pl-sp-env-uni1 "R")))
+  ".(1, .(2, .(3, .(4, []))))")
+
+(define pl-sp-env-uni2 {:R (pl-mk-rt-var "R")})
+(pl-solve-once!
+  pl-sp-db
+  (pl-sp-goal "union([], [1,2], R)" pl-sp-env-uni2)
+  (pl-mk-trail))
+(pl-sp-test!
+  "union([],[1,2],R) -> [1,2]"
+  (pl-format-term (pl-walk-deep (dict-get pl-sp-env-uni2 "R")))
+  ".(1, .(2, []))")
+
+(define pl-sp-env-uni3 {:R (pl-mk-rt-var "R")})
+(pl-solve-once!
+  pl-sp-db
+  (pl-sp-goal "union([1,2], [], R)" pl-sp-env-uni3)
+  (pl-mk-trail))
+(pl-sp-test!
+  "union([1,2],[],R) -> [1,2]"
+  (pl-format-term (pl-walk-deep (dict-get pl-sp-env-uni3 "R")))
+  ".(1, .(2, []))")
+
+;; ── Runner ─────────────────────────────────────────────────────────
+
+(define pl-set-predicates-tests-run! (fn () {:failed pl-sp-test-fail :passed pl-sp-test-pass :total pl-sp-test-count :failures pl-sp-test-failures}))