add tests to check known counterexamples to seeming equivalences

qi-test/tests/flow.rkt

@@ -1483,7 +1483,32 @@
     (check-equal? ((☯ (~> (pass positive?) +))
                    1 -3 5)
                   6
-                  "runtime arity changes in threading form"))))
+                  "runtime arity changes in threading form"))
+
+   (test-suite
+    "nonlocal semantics"
+    ;; these are collected from counterexamples to candidate equivalences
+    ;; that turned up during code review. They ensure that some tempting
+    ;; "equivalences" that are not really equivalences are formally checked
+    (let ()
+      (define-flow g (-< add1 sub1))
+      (define-flow f positive?)
+      (define (f* x y) (= (sub1 x) (add1 y)))
+      (define (amp-pass g f) (☯ (~> (>< g) (pass f) ▽)))
+      (define (amp-if g f) (☯ (~> (>< (~> g (if f _ ground))) ▽)))
+      (check-equal? (apply (amp-pass g f) (range -3 4))
+                    (list 1 2 3 1 4 2))
+      (check-exn exn:fail?
+                 (thunk (apply (amp-if g f) (range -3 4))))
+      (check-exn exn:fail?
+                 (thunk (apply (amp-pass g f*) (range -3 4))))
+      (check-equal? (apply (amp-if g f*) (range -3 4))
+                    (list -2 -4 -1 -3 0 -2 1 -1 2 0 3 1 4 2)))
+    (let ()
+      (check-equal? ((☯ (~> (>< string->number) (pass _))) "a" "2" "c")
+                    2)
+      (check-equal? ((☯ (~> (>< (if _ string->number ground)) ▽)) "a" "2" "c")
+                    (list #f 2 #f))))))
 
 (module+ main
   (void (run-tests tests)))