diff --git a/2019/09.rkt b/2019/09.rkt
index 5bf49b5..3766707 100644
--- a/2019/09.rkt
+++ b/2019/09.rkt
@@ -21,9 +21,9 @@
                  (reg-ref ptr)]))
             (define (reg-set! ptr val)
               (cond
-                [(< (reg-ref ptr) (vector-length regs)) (vector-set! regs (reg-ref ptr) val)]
+                [(< ptr (vector-length regs)) (vector-set! regs ptr val)]
                 [else
-                 (grow-regs! (add1 (reg-ref ptr)))
+                 (grow-regs! (add1 ptr))
                  (reg-set! ptr val)]))
             (define relative-base 0)
             (let/ec terminate
@@ -31,30 +31,30 @@
                 (define inst (for/list ([c (in-string (~r (reg-ref ptr) #:min-width 5 #:pad-string "0"))])
                                (string->number (string c))))
                 (match-define (list opcode mode-1 mode-2 mode-3)
-                  (match #R inst
+                  (match inst
                     [(list d4 d3 d2 d1 d0)
                      (cons (+ (* 10 d1) d0)
                            (for/list ([mode-val (list d2 d3 d4)]
                                       [offset '(1 2 3)])
-                             (match mode-val
-                               ;; position
-                               [0 (λ (ptr) (reg-ref (reg-ref (+ ptr offset))))]
-                               ;; immediate
-                               [1 (λ (ptr) (reg-ref (+ ptr offset)))]
-                               ;; relative
-                               [2 (λ (ptr) (reg-ref (+ relative-base (reg-ref (+ ptr offset)))))])))]))
+                             (λ (ptr [io-mode? 'read])
+                               ((if (eq? io-mode? 'read) reg-ref values)
+                                (let ([ptr-adjusted (+ ptr offset)])
+                                  (match mode-val
+                                    [0 (reg-ref ptr-adjusted)] ; position
+                                    [1 ptr-adjusted] ; immediate
+                                    [2 (+ relative-base (reg-ref ptr-adjusted))]))))))])) ; relative
                 (define next-ptr
-                  (match #R opcode
+                  (match opcode
                     [(or 1 2 7 8) ; 4-arity: add & multiply & compare
-                     (reg-set! (+ ptr 3) ((match opcode
-                                            [1 +]
-                                            [2 *]
-                                            [7 (binarize <)]
-                                            [8 (binarize =)]) (mode-1 ptr) (mode-2 ptr)))
+                     (reg-set! (mode-3 ptr 'write) ((match opcode
+                                                  [1 +]
+                                                  [2 *]
+                                                  [7 (binarize <)]
+                                                  [8 (binarize =)]) (mode-1 ptr) (mode-2 ptr)))
                      (+ ptr 4)]
                     [(or 3 4 9) ; 2-arity: input & output
                      (match opcode
-                       [3 (reg-set! (mode-1 ptr) (thread-receive))]
+                       [3 (reg-set! (mode-1 ptr 'write) (thread-receive))]
                        [4 (thread-send calling-thd (mode-1 ptr))]
                        [9 (set! relative-base (+ relative-base (mode-1 ptr)))])
                      (+ ptr 2)]
@@ -83,6 +83,7 @@
  (run "109,1,204,-1,1001,100,1,100,1008,100,16,101,1006,101,0,99")
  '(109 1 204 -1 1001 100 1 100 1008 100 16 101 1006 101 0 99))
 
+
 (check-equal?
  (run "1102,34915192,34915192,7,4,7,99,0")
  '(1219070632396864))
@@ -91,7 +92,8 @@
  (run "104,1125899906842624,99")
  '(1125899906842624))
 
-
 (define t1 (make-runner (file->string "09.rktd")))
 (thread-send t1 1)
-(run t1)
+(check-equal?
+ (run t1)
+ '(3601950151))