Improve types for exit and in-naturals.

collects/tests/typed-racket/succeed/for.rkt

@@ -226,6 +226,12 @@
        (vector 5 5 5))
 
 
+(check equal?
+       (for/list: : (Listof Natural)
+                  ((i : Natural (and (in-naturals)))
+                   (j : Natural (and (in-range 5))))
+             (+ i j))
+       (list 0 2 4 6 8))
 
 ;; break and final clauses
 ;; TODO typechecker can't handle these

collects/typed-racket/base-env/base-env.rkt

@@ -1129,7 +1129,7 @@
 
 
 ;Section 9.7 (Exiting)
-[exit (-> (Un))]
+[exit (->opt [Univ] (Un))]
 [exit-handler (-Param (-> Univ ManyUniv) (-> Univ ManyUniv))]
 [executable-yield-handler (-Param (-> -Byte ManyUniv) (-> -Byte ManyUniv))]
 

collects/typed-racket/base-env/base-special-env.rkt

@@ -84,7 +84,8 @@
           (->opt -Real -Real [-Real] (-seq -Real)))]
   ;; in-naturals
   [(make-template-identifier 'in-naturals 'racket/private/for)
-   (cl->* (-> -PosInt (-seq -PosInt))
+   (cl->* (-> (-seq -Nat))
+          (-> -PosInt (-seq -PosInt))
           (-> -Int (-seq -Nat)))]
   ;; in-list
   [(make-template-identifier 'in-list 'racket/private/for)