diff --git a/bin/day2403.ml b/bin/day2403.ml
index 010736d..531de90 100644
--- a/bin/day2403.ml
+++ b/bin/day2403.ml
@@ -1,6 +1,4 @@
-(** [matched_group_opt n s] returns [Some (Str.matched_group n s)] if the [n]th
-    group matched, or [None] if the group did not match. *)
-let matched_group_opt n s = try Some (Str.matched_group n s) with _ -> None
+type cmd = Do | Donot | Mul of int * int
 
 (** [find_nums s] returns the list of instructions given in [s]. *)
 let instrs_of_string s =
@@ -11,12 +9,16 @@ let instrs_of_string s =
   let rec impl acc pos =
     try
       let _ = Str.search_forward r s pos in
-      let p0 = Str.matched_group 0 s in
-      let p1 = matched_group_opt 1 s in
-      let p2 = matched_group_opt 2 s in
-      impl
-        ((p0, Option.map int_of_string p1, Option.map int_of_string p2) :: acc)
-        (Str.match_end ())
+      let action =
+        match Str.matched_group 0 s with
+        | "do()" -> Do
+        | "don't()" -> Donot
+        | _ ->
+            Mul
+              ( int_of_string (Str.matched_group 1 s),
+                int_of_string (Str.matched_group 2 s) )
+      in
+      impl (action :: acc) (Str.match_end ())
     with Not_found -> acc
   in
   List.rev (impl [] 0)
@@ -24,20 +26,18 @@ let instrs_of_string s =
 let instrs_of_file fname =
   Aoc.strings_of_file fname |> List.map instrs_of_string |> List.concat
 
-(** [mac_opt acc a b] returns [acc + a' * b'] if [a = Some a'] and 
-    [b = Some b'].  If either [a] or [b] are [None] then the result is [acc]. *)
-let mac_opt acc a b =
-  acc + (Option.value a ~default:0 * Option.value b ~default:0)
+(** [mac acc a b] returns [acc + a * b]. *)
+let mac acc = function Mul (a, b) -> acc + (a * b) | _ -> acc
 
-let day2403a = List.fold_left (fun acc (_, a, b) -> mac_opt acc a b) 0
+let day2403a = List.fold_left mac 0
 
 let day2403b lst =
   let rec impl acc enabled = function
     | [] -> acc
-    | ("do()", _, _) :: t -> impl acc true t
-    | ("don't()", _, _) :: t -> impl acc false t
-    | (_, a, b) :: t ->
-        if enabled then impl (mac_opt acc a b) true t else impl acc false t
+    | Do :: t -> impl acc true t
+    | Donot :: t -> impl acc false t
+    | Mul (a, b) :: t ->
+        if enabled then impl (acc + (a * b)) true t else impl acc false t
   in
   impl 0 true lst