prolog: write/1 + nl/0 via output buffer, 7 tests; built-ins box done

lib/prolog/tests/solve.sx

@@ -421,4 +421,78 @@
     (pl-mk-trail))
   false)
 
+(pl-s-test!
+  "write(hello)"
+  (begin
+    (pl-output-clear!)
+    (pl-solve-once!
+      pl-s-empty-db
+      (pl-s-goal "write(hello)" {})
+      (pl-mk-trail))
+    pl-output-buffer)
+  "hello")
+
+(pl-s-test!
+  "nl outputs newline"
+  (begin
+    (pl-output-clear!)
+    (pl-solve-once! pl-s-empty-db (pl-s-goal "nl" {}) (pl-mk-trail))
+    pl-output-buffer)
+  "\n")
+
+(pl-s-test!
+  "write(42) outputs digits"
+  (begin
+    (pl-output-clear!)
+    (pl-solve-once!
+      pl-s-empty-db
+      (pl-s-goal "write(42)" {})
+      (pl-mk-trail))
+    pl-output-buffer)
+  "42")
+
+(pl-s-test!
+  "write(foo(a, b)) formats compound"
+  (begin
+    (pl-output-clear!)
+    (pl-solve-once!
+      pl-s-empty-db
+      (pl-s-goal "write(foo(a, b))" {})
+      (pl-mk-trail))
+    pl-output-buffer)
+  "foo(a, b)")
+
+(pl-s-test!
+  "write conjunction"
+  (begin
+    (pl-output-clear!)
+    (pl-solve-once!
+      pl-s-empty-db
+      (pl-s-goal "write(a), write(b)" {})
+      (pl-mk-trail))
+    pl-output-buffer)
+  "ab")
+
+(pl-s-test!
+  "write of bound var walks binding"
+  (begin
+    (pl-output-clear!)
+    (pl-solve-once!
+      pl-s-empty-db
+      (pl-s-goal "=(X, hello), write(X)" {})
+      (pl-mk-trail))
+    pl-output-buffer)
+  "hello")
+
+(pl-s-test!
+  "write then nl"
+  (begin
+    (pl-output-clear!)
+    (pl-solve-once!
+      pl-s-empty-db
+      (pl-s-goal "write(hi), nl" {})
+      (pl-mk-trail))
+    pl-output-buffer)
+  "hi\n")
+
 (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}))