day 13 but not stupid

src/day13/Day13Lib.hs

@@ -8,7 +8,6 @@ module Day13Lib
   )
 where
 
--- import Data.Either
 import Data.List
 import Data.List.Split (splitOn)
 import Debug.Trace
@@ -16,6 +15,17 @@ import Text.Parsec
 
 data Value = Num Int | List [Value] deriving (Show, Eq)
 
+instance Ord Value where
+  compare (Num x) (Num y) = compare x y
+  compare x@(Num _) y@(List _) = compare (List [x]) y
+  compare x@(List _) y@(Num _) = compare x (List [y])
+  compare (List (x : xs)) (List (y : ys)) = case compare x y of
+    EQ -> compare (List xs) (List ys)
+    o -> o
+  compare (List []) (List (y : ys)) = LT
+  compare (List (x : xs)) (List []) = GT
+  compare (List []) (List []) = EQ
+
 parseList :: Parsec String () Value
 parseList = do
   char '['
@@ -28,17 +38,6 @@ parseNumber = do
   ns <- try . many1 $ digit
   return $ Num (read ns)
 
-cmp :: Value -> Value -> Ordering
-cmp (Num x) (Num y) = compare x y
-cmp x@(Num _) y@(List _) = cmp (List [x]) y
-cmp x@(List _) y@(Num _) = cmp x (List [y])
-cmp (List (x : xs)) (List (y : ys)) = case cmp x y of
-  EQ -> cmp (List xs) (List ys)
-  o -> o
-cmp (List []) (List (y : ys)) = LT
-cmp (List (x : xs)) (List []) = GT
-cmp (List []) (List []) = EQ
-
 runParse :: String -> Value
 runParse s = case parse parseList "" s of
   Left e -> error $ "parse error: " ++ show e
@@ -49,19 +48,16 @@ runParse s = case parse parseList "" s of
 processInput1 :: String -> Int
 processInput1 =
   sum
-    . zipWith (\x y -> if y == LT then x else 0) [1 ..]
+    . zipWith (\x [v1, v2] -> if v1 < v2 then x else 0) [1 ..]
     . map
-      ( (\[x, y] -> cmp x y)
-          . map runParse
-          . lines
-      )
+      (map runParse . lines)
     . splitOn "\n\n"
 
 processInput2 :: String -> Int
 processInput2 =
   product
     . zipWith (\x y -> if y `elem` dividers then x else 1) [1 ..]
-    . sortBy cmp
+    . sort
     . (++) dividers
     . (concatMap (map runParse . lines) . splitOn "\n\n")