prolog: cut !/0 with two-cut-box barrier scheme, 6 tests

lib/prolog/tests/solve.sx

@@ -181,4 +181,63 @@
   (pl-var-bound? (dict-get pl-s-env-undo "X"))
   false)
 
+(define pl-s-db-cut1 (pl-mk-db))
+
+(pl-db-load! pl-s-db-cut1 (pl-parse "g :- !. g :- true."))
+
+(pl-s-test!
+  "bare cut succeeds"
+  (pl-solve-once! pl-s-db-cut1 (pl-s-goal "g" {}) (pl-mk-trail))
+  true)
+
+(pl-s-test!
+  "cut commits to first matching clause"
+  (pl-solve-count! pl-s-db-cut1 (pl-s-goal "g" {}) (pl-mk-trail))
+  1)
+
+(define pl-s-db-cut2 (pl-mk-db))
+
+(pl-db-load! pl-s-db-cut2 (pl-parse "a(1). a(2). g(X) :- a(X), !."))
+
+(pl-s-test!
+  "cut commits to first a solution"
+  (pl-solve-count! pl-s-db-cut2 (pl-s-goal "g(X)" {}) (pl-mk-trail))
+  1)
+
+(define pl-s-db-cut3 (pl-mk-db))
+
+(pl-db-load!
+  pl-s-db-cut3
+  (pl-parse "a(1). a(2). g(X) :- a(X), !, fail. g(99)."))
+
+(pl-s-test!
+  "cut then fail blocks alt clauses"
+  (pl-solve-count! pl-s-db-cut3 (pl-s-goal "g(X)" {}) (pl-mk-trail))
+  0)
+
+(define pl-s-db-cut4 (pl-mk-db))
+
+(pl-db-load!
+  pl-s-db-cut4
+  (pl-parse "a(1). b(10). b(20). g(X, Y) :- a(X), !, b(Y)."))
+
+(pl-s-test!
+  "post-cut goal backtracks freely"
+  (pl-solve-count!
+    pl-s-db-cut4
+    (pl-s-goal "g(X, Y)" {})
+    (pl-mk-trail))
+  2)
+
+(define pl-s-db-cut5 (pl-mk-db))
+
+(pl-db-load!
+  pl-s-db-cut5
+  (pl-parse "r(1). r(2). q :- r(X), !. p :- q. p :- true."))
+
+(pl-s-test!
+  "inner cut does not commit outer predicate"
+  (pl-solve-count! pl-s-db-cut5 (pl-s-goal "p" {}) (pl-mk-trail))
+  2)
+
 (define pl-solve-tests-run! (fn () {:failed pl-s-test-fail :passed pl-s-test-pass :total pl-s-test-count :failures pl-s-test-failures}))