diff --git a/simulator-structs.rkt b/simulator-structs.rkt
index e182bd1..a0d5fa7 100644
--- a/simulator-structs.rkt
+++ b/simulator-structs.rkt
@@ -16,14 +16,20 @@
   #:transparent)
 
 
-(define-struct: frame ([return : Symbol])
+(define-struct: frame ([return : Symbol]
+                       ;; TODO: add continuation marks
+                       )
   #:transparent)
 
 (define-struct: toplevel ([vals : (Vectorof Any)])
   #:transparent)
 
+
 ;; Primitive procedure wrapper
-(define-struct: primitive-proc ([f : (Any * -> Any)]))
-
-
+(define-struct: primitive-proc ([f : (Any * -> Any)])
+  #:transparent)
 
+;; Compiled procedure closures
+(define-struct: closure ([label : Symbol]
+                         [vals : (Listof Any)])
+  #:transparent)
diff --git a/simulator.rkt b/simulator.rkt
index 51a9f92..aa8a35b 100644
--- a/simulator.rkt
+++ b/simulator.rkt
@@ -12,7 +12,7 @@
          (for-syntax racket/base))
 
 (require/typed "simulator-prims.rkt"
-               [lookup-primitive (Symbol -> (Any * -> Any))])
+               [lookup-primitive (Symbol -> Any)])
                
 
 (provide new-machine can-step? step)
@@ -43,7 +43,7 @@
            [(AssignPrimOpStatement? i)
             (error 'step)]
            [(PerformStatement? i)
-            (error 'step)]
+            (step-perform m i)]
            [(GotoStatement? i)
             (step-goto m i)]
            [(TestAndBranchStatement? i)
@@ -132,6 +132,24 @@
          (machine-val m)]
         [(eq? reg 'proc)
          (machine-proc m)]))
+
+
+(: step-perform (machine PerformStatement -> machine))
+(define (step-perform m stmt)
+  (let: ([op : PrimitiveCommand (PerformStatement-op stmt)])
+        (cond
+          [(SetToplevel!? op)
+           (error 'step-perform)]
+          [(CheckToplevelBound!? op)
+           (error 'step-perform)]
+          [(ExtendEnvironment/Prefix!? op)
+           (env-push m 
+                     (make-toplevel (list->vector
+                                     (map lookup-primitive 
+                                          (ExtendEnvironment/Prefix!-names op)))))]
+          [(InstallClosureValues!? op)
+           (error 'step-perform)])))
+
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
 
diff --git a/test-simulator.rkt b/test-simulator.rkt
index b019b26..d0bb6f7 100644
--- a/test-simulator.rkt
+++ b/test-simulator.rkt
@@ -11,12 +11,7 @@
     [(_ actual exp)
      (with-syntax ([stx stx])
        (syntax/loc #'stx
-         (let ([results (with-handlers ([exn:fail?
-                                         (lambda (exn)
-                                           (raise-syntax-error #f (format "Exception happened: ~s" 
-                                                                          (exn-message exn))
-                                                               #'stx))])
-                          actual)])
+         (let ([results actual])
            (unless (equal? actual exp)
              (raise-syntax-error #f (format "Expected ~s, got ~s" exp results)
                                  #'stx)))))]))
@@ -227,8 +222,8 @@
 
 ;; AssignPrimOpStatement
 (let ([m (new-machine `(,(make-PerformStatement (make-ExtendEnvironment/Prefix! '(+ - * =)))))])
-  (test (machine-env (run m))
-        (list (make-toplevel (vector (lookup-primitive +)
-                                     (lookup-primitive -)
-                                     (lookup-primitive *)
-                                     (lookup-primitive =))))))
\ No newline at end of file
+  (test (first (machine-env (run m)))
+        (make-toplevel (vector (lookup-primitive '+)
+                               (lookup-primitive '-)
+                               (lookup-primitive '*)
+                               (lookup-primitive '=)))))
\ No newline at end of file