fixing a bug with boxenv

compile.rkt

@@ -89,7 +89,7 @@
           [(InstallValue? exp)
            (loop (InstallValue-body exp) cenv)]
           [(BoxEnv? exp)
-           '()]
+           (loop (BoxEnv-body exp) cenv)]
           [(LetRec? exp)
            (let ([new-cenv (append (map (lambda: ([p : Lam]) 
                                                  (extract-static-knowledge 

test-compiler.rkt

@@ -790,6 +790,14 @@
         #:control-limit 3)
 
 
+(test '(begin (define counter
+                (let ([x 0])
+                  (lambda ()
+                    (set! x (add1 x))
+                    x)))
+              (list (counter) (counter) (counter)))
+      '(1 2 3))
+