[regexp] set! already breaks type, dont need extra transformer I guess

test/regexp-fail.rkt

@@ -33,6 +33,11 @@
          (define rx "he(l*)(o*)")
          (regexp-match: rx "helloooooooo"))
        (U #f (List String String String)))
+  ;; -- set! problems
+  (ann (let-regexp: ([a #rx"(b)(B)"])
+         (set! a #rx"")
+         (regexp-match: a "hai"))
+       (List String String String))
   ;; --- Can't handle |, yet
   (ann (regexp-match: "this(group)|that" "that")
        (U #f (List String String)))

test/regexp-pass.rkt

@@ -8,6 +8,24 @@
     trivial/regexp
     typed/rackunit)
 
+  ;; -- set! ruins everything
+  (check-equal?
+    (ann
+      (let ()
+        (define-regexp: a #rx"h(i)")
+        (set! a #rx"hi")
+        (regexp-match a "hi"))
+      (U #f (Pairof String (Listof (U #f String)))))
+    (list "hi"))
+
+  (check-equal?
+    (ann
+      (let-regexp: ([a #rx"h(i)"])
+        (set! a #rx"(h)(i)")
+        (regexp-match a "hi"))
+      (U #f (Pairof String (Listof (U #f String)))))
+    (list "hi" "h" "i"))
+
   ;; -- regexp-match:
   (check-equal?
     (ann