day 8: ok this one is actually better

8.rkt

@@ -8,55 +8,43 @@
 
 ;; helper functions here
 
-(define (part1 input)
+(define (execute-program prg)
   (define (execute pc acc [seen (mutable-set)])
-    (if (set-member? seen pc)
-      acc
-      (let ([in (list-ref input pc)])
-        (set-add! seen pc)
-        (match (insn-type in)
-          ["nop" (execute (add1 pc) acc seen)]
-          ["jmp" (execute (+ pc (insn-arg in)) acc seen)]
-          ["acc" (execute (add1 pc) (+ acc (insn-arg in)) seen)]
-          [x (error "not shonks" x)]))))
+    (cond
+      [(set-member? seen pc) (cons 'loop acc)]
+      [(>= pc (vector-length prg)) (cons 'done acc)]
+      [else
+       (match-define (insn type arg) (vector-ref prg pc))
+       (set-add! seen pc)
+       (match type
+         ["nop" (execute (add1 pc) acc seen)]
+         ["jmp" (execute (+ pc arg) acc seen)]
+         ["acc" (execute (add1 pc) (+ acc arg) seen)])]))
   (execute 0 0))
 
+(define (part1 input)
+  (cdr (execute-program input)))
+
 (define (part2 input)
-  (define (execute-actual input)
-    (define (execute pc acc [seen (mutable-set)])
-      (if (>= pc (length input))
-        acc
-        (let ([in (list-ref input pc)])
-          (set-add! seen pc)
-          (match (insn-type in)
-            ["nop" (execute (add1 pc) acc seen)]
-            ["jmp" (execute (+ pc (insn-arg in)) acc seen)]
-            ["acc" (execute (add1 pc) (+ acc (insn-arg in)) seen)]
-            [x (error "not shonks" x)]))))
-    (execute 0 0))
-
-  (define target-pc (length input))
-  (for ([in (in-list input)] [i (in-naturals)] #:unless (string=? "acc" (insn-type in)))
-    (define new-type (if (string=? (insn-type in) "jmp") "nop" "jmp"))
-    (define new-insn (insn new-type (insn-arg in)))
-    ;; aaaa
-    (define vec (vector-copy (list->vector input)))
-    (vector-set! vec i new-insn)
-    (define new-prg (vector->list vec))
-    (with-handlers ([exn? (lambda (x) (answer 8 2 (execute-actual new-prg)))])
-      (part1 new-prg))))
-
-(module+ test
-  (require rackunit)
-  ;; tests here
-  (displayln "no tests :("))
+  (let/ec exit
+    (for ([ins (in-vector input)] [i (in-naturals)]
+          #:unless (string=? "acc" (insn-type ins)))
+      (define new-insn
+        (insn (match (insn-type ins) ["jmp" "nop"] ["nop" "jmp"])
+              (insn-arg ins)))
+      (define new-prg (vector-copy input))
+      (vector-set! new-prg i new-insn)
+      (match (execute-program new-prg)
+        [(cons 'loop _) (void)]
+        [(cons 'done acc) (exit acc)]))))
 
 (module+ main
   (define input
-    (for/list ([line (in-list (file->lines "inputs/8"))])
+    (for/vector ([line (in-list (file->lines "inputs/8"))])
       (match (string-split line)
         [(list a b) (insn a (string->number b))]
         [x (error "not shonks" x)])))
+
   ;; part 1
   (answer 8 1 (part1 input))