a bit less unpacking.

sorta overkill. I like the idea that you just express the
intention through Monoid and let foldMap have at it.

src/Javran/AdventOfCode/Y2023/Day1.hs

@@ -1,6 +1,7 @@
 module Javran.AdventOfCode.Y2023.Day1 () where
 
 import Data.Char
+import Data.Coerce (coerce)
 import Data.List
 import Data.Semigroup
 import Javran.AdventOfCode.Prelude
@@ -46,12 +47,12 @@ getDigits2 = mapMaybe parse . tails
     parse = consumeAllWithReadP (oneDigitP <* munch (\_ -> True))
 
 solve :: (String -> [Int]) -> [String] -> Int
-solve df = sum . fmap (combine . foldMap collector . df)
+solve df = getSum . foldMap (coerce combine . foldMap collector . df)
   where
     -- just to collect both first and last value with a single traverse.
     collector = (,) <$> Just . First <*> Just . Last
     combine = \case
-      (Just (First a), Just (Last b)) -> a * 10 + b
+      (Just a, Just b) -> a * 10 + b :: Int
       _ ->
         {-
           Note that this branch is usually unreachable as login input will always