Add convenience enumerator approximation function

pkgs/redex-pkgs/redex-lib/redex/private/enumerator.rkt

@@ -38,6 +38,7 @@
          
          fail/e
          
+         approximate
          to-list
          take/e
          fold-enum
@@ -132,6 +133,10 @@
          e
          excepts))
 
+(define (approximate e n)
+  (for/list ([i (in-range n)])
+    (decode e i)))
+
 ;; to-list : enum a -> listof a
 ;; better be finite
 (define (to-list e)