From 285da9a99af35206126ee5dbd510523ea4620e40 Mon Sep 17 00:00:00 2001
From: Matthew Butterick <mb@mbtype.com>
Date: Mon, 9 Dec 2019 16:46:13 -0800
Subject: [PATCH] tidy

---
 2019/09.rkt | 39 +++++++++++++++++++--------------------
 1 file changed, 19 insertions(+), 20 deletions(-)

diff --git a/2019/09.rkt b/2019/09.rkt
index 70d8d53..2ae708b 100644
--- a/2019/09.rkt
+++ b/2019/09.rkt
@@ -22,38 +22,37 @@
               (let loop ([ptr 0])
                 (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)
+                (define-values (opcode resolve)
                   (match inst
                     [(list d4 d3 d2 d1 d0)
-                     (cons (+ (* 10 d1) d0)
-                           (for/list ([mode-val (list d2 d3 d4)]
-                                      [offset '(1 2 3)])
-                                     (λ (ptr)
-                                       (define 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
+                     (values (+ (* 10 d1) d0)
+                             (λ (ptr offset)
+                               (define parameter-value (match offset [1 d2] [2 d3] [3 d4]))
+                               (define ptr-resolver (match parameter-value
+                                                      [0 reg-ref] ; position
+                                                      [1 values] ; immediate
+                                                      [2 (compose1 (λ (ptr) (+ relative-base ptr)) reg-ref)])); relative
+                               (ptr-resolver (+ ptr offset))))])) 
                 (define next-ptr
                   (match opcode
                     [(or 1 2 7 8) ; 4-arity: add & multiply & compare
-                     (reg-set! (mode-3 ptr) ((match opcode
-                                               [1 +]
-                                               [2 *]
-                                               [7 (binarize <)]
-                                               [8 (binarize =)]) (reg-ref (mode-1 ptr)) (reg-ref (mode-2 ptr))))
+                     (reg-set! (resolve ptr 3) ((match opcode
+                                                  [1 +]
+                                                  [2 *]
+                                                  [7 (binarize <)]
+                                                  [8 (binarize =)]) (reg-ref (resolve ptr 1)) (reg-ref (resolve ptr 2))))
                      (+ ptr 4)]
                     [(or 3 4 9) ; 2-arity: input & output
                      (match opcode
-                       [3 (reg-set! (mode-1 ptr) (thread-receive))]
-                       [4 (thread-send calling-thd (reg-ref (mode-1 ptr)))]
-                       [9 (set! relative-base (+ relative-base (reg-ref (mode-1 ptr))))])
+                       [3 (reg-set! (resolve ptr 1) (thread-receive))]
+                       [4 (thread-send calling-thd (reg-ref (resolve ptr 1)))]
+                       [9 (set! relative-base (+ relative-base (reg-ref (resolve ptr 1))))])
                      (+ ptr 2)]
                     [(or 5 6) ; 3-arity: jump
                      (if ((match opcode
                             [5 not]
-                            [6 values]) (zero? (reg-ref (mode-1 ptr))))
-                         (reg-ref (mode-2 ptr))
+                            [6 values]) (zero? (reg-ref (resolve ptr 1))))
+                         (reg-ref (resolve ptr 2))
                          (+ ptr 3))]
                     [99 (thread-send calling-thd 'done) (terminate)]
                     [_ (error "unknown opcode" opcode)]))