diff --git a/bin/day2401.ml b/bin/day2401.ml
index a0ed08f..0d51610 100644
--- a/bin/day2401.ml
+++ b/bin/day2401.ml
@@ -28,22 +28,12 @@ let accumulate = List.fold_left ( + ) 0
 let lists_from_file fname =
   Aoc.strings_from_file fname |> List.map pair_nums_from_string |> rev_split
 
-let day2401a a b =
+let day2401a (a, b) =
   List.map2 Aoc.distance1 (List.sort Int.compare a) (List.sort Int.compare b)
   |> accumulate
 
-let day2401b a b = List.map (count b) a |> List.map2 ( * ) a |> accumulate
+let day2401b (a, b) = List.map (count b) a |> List.map2 ( * ) a |> accumulate
 
 let _ =
-  try
-    match Sys.argv with
-    | [| _; fname |] ->
-        let a, b = lists_from_file fname in
-        Printf.printf "Part 1 = %d\n" (day2401a a b);
-        Printf.printf "Part 2 = %d\n" (day2401b a b)
-    | _ ->
-        Printf.printf "Usage: day2401 <fname>\n";
-        exit 1
-  with e ->
-    Printf.printf "An error occured: %s\n" (Printexc.to_string e);
-    exit 1
+  Aoc.main lists_from_file
+    [ (string_of_int, day2401a); (string_of_int, day2401b) ]
diff --git a/bin/day2402.ml b/bin/day2402.ml
index 5e70a74..d4e76cd 100644
--- a/bin/day2402.ml
+++ b/bin/day2402.ml
@@ -22,15 +22,5 @@ let day2402a lsts = List.filter is_safe lsts |> List.length
 let day2402b lsts = List.filter is_safe_dampened lsts |> List.length
 
 let _ =
-  try
-    match Sys.argv with
-    | [| _; fname |] ->
-        let lines = nums_from_file fname in
-        Printf.printf "Part 1 = %d\n" (day2402a lines);
-        Printf.printf "Part 2 = %d\n" (day2402b lines)
-    | _ ->
-        Printf.printf "Usage: day2402 <fname>\n";
-        exit 1
-  with e ->
-    Printf.printf "An error occured: %s\n" (Printexc.to_string e);
-    exit 1
+  Aoc.main nums_from_file
+    [ (string_of_int, day2402a); (string_of_int, day2402b) ]
diff --git a/lib/aoc.ml b/lib/aoc.ml
index cb7dff6..05a23c4 100644
--- a/lib/aoc.ml
+++ b/lib/aoc.ml
@@ -3,3 +3,20 @@ let distance1 a b = abs (a - b)
 
 let strings_from_file fname =
   In_channel.with_open_text fname In_channel.input_lines
+
+let main prep parts =
+  try
+    match Sys.argv with
+    | [| _; fname |] ->
+        let lines = prep fname in
+        let do_part i (fmt, fn) =
+          Printf.printf "Part %d = %s\n" i (fmt (fn lines))
+        in
+        List.iteri do_part parts;
+        exit 0
+    | _ ->
+        Printf.printf "Usage: %s <fname>\n" Sys.executable_name;
+        exit 2
+  with e ->
+    Printf.printf "An error occured: %s\n" (Printexc.to_string e);
+    exit 1
diff --git a/lib/aoc.mli b/lib/aoc.mli
index b875046..d5b6fc4 100644
--- a/lib/aoc.mli
+++ b/lib/aoc.mli
@@ -8,3 +8,11 @@ val distance1 : int -> int -> int
 val strings_from_file : string -> string list
 (** [strings_from_file fname] returns a list of strings from the file 
     [fname].  Each string represents a line from the file. *)
+
+val main : (string -> 'a) -> (('b -> string) * ('a -> 'b)) list -> unit
+(** [main prep parts] executes an advent of code problem.  [prep fname] should
+    be a function that returns the input from [fname].  Each elemet of
+    [parts] is a pair of functions.  The first converts the output to a string
+    (for example [string_of_int]).  The second executes the given part.
+    Output is given as if done by: 
+    [print_string ( prep fname |> snd |> fst )] *)