prolog: ->/2 if-then-else (in ; and standalone), 9 tests

lib/prolog/tests/solve.sx

@@ -337,4 +337,88 @@
     (pl-mk-trail))
   true)
 
+(define pl-s-db-ite (pl-mk-db))
+
+(pl-db-load! pl-s-db-ite (pl-parse "p(1). p(2). q(yes). q(no)."))
+
+(pl-s-test!
+  "if-then-else: cond true → then runs"
+  (pl-solve-once!
+    pl-s-db-ite
+    (pl-s-goal ";(->(true, =(X, ok)), =(X, fallback))" {})
+    (pl-mk-trail))
+  true)
+
+(define pl-s-env-ite1 {})
+
+(pl-solve-once!
+  pl-s-db-ite
+  (pl-s-goal ";(->(true, =(X, ok)), =(X, fallback))" pl-s-env-ite1)
+  (pl-mk-trail))
+
+(pl-s-test!
+  "if-then-else: cond true binds via then"
+  (pl-atom-name (pl-walk-deep (dict-get pl-s-env-ite1 "X")))
+  "ok")
+
+(pl-s-test!
+  "if-then-else: cond false → else"
+  (pl-solve-once!
+    pl-s-db-ite
+    (pl-s-goal ";(->(fail, =(X, ok)), =(X, fallback))" {})
+    (pl-mk-trail))
+  true)
+
+(define pl-s-env-ite2 {})
+
+(pl-solve-once!
+  pl-s-db-ite
+  (pl-s-goal ";(->(fail, =(X, ok)), =(X, fallback))" pl-s-env-ite2)
+  (pl-mk-trail))
+
+(pl-s-test!
+  "if-then-else: cond false binds via else"
+  (pl-atom-name (pl-walk-deep (dict-get pl-s-env-ite2 "X")))
+  "fallback")
+
+(pl-s-test!
+  "if-then-else: cond commits to first solution (count = 1)"
+  (pl-solve-count!
+    pl-s-db-ite
+    (pl-s-goal ";(->(p(X), =(Y, found)), =(Y, none))" {})
+    (pl-mk-trail))
+  1)
+
+(pl-s-test!
+  "if-then-else: then can backtrack"
+  (pl-solve-count!
+    pl-s-db-ite
+    (pl-s-goal ";(->(true, p(X)), =(X, none))" {})
+    (pl-mk-trail))
+  2)
+
+(pl-s-test!
+  "if-then-else: else can backtrack"
+  (pl-solve-count!
+    pl-s-db-ite
+    (pl-s-goal ";(->(fail, =(X, ignored)), p(X))" {})
+    (pl-mk-trail))
+  2)
+
+(pl-s-test!
+  "standalone -> with true cond succeeds"
+  (pl-solve-once!
+    pl-s-db-ite
+    (pl-s-goal "->(true, =(X, hi))" {})
+    (pl-mk-trail))
+  true)
+
+(pl-s-test!
+  "standalone -> with false cond fails"
+  (pl-solve-once!
+    pl-s-db-ite
+    (pl-s-goal "->(fail, =(X, hi))" {})
+    (pl-mk-trail))
+  false)
+
 (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}))