Part 1 done

aoc.cabal

@@ -102,6 +102,7 @@ executable 9
     -- other-extensions:
     build-depends:    base ^>=4.18.2.1
                     , split
+                    , extra
     hs-source-dirs:   app
     default-language: GHC2021
 executable 10

app/9.hs

@@ -2,14 +2,36 @@
 module Main where
 
 import Data.Functor
+import Data.List
+import Data.List.Extra
 
-parse = undefined
+data ℜ where
+  None :: ℜ
+  Num  :: Int -> ℜ
+    deriving Eq
 
-solve1 = undefined
+instance Show ℜ where
+  show None = show '.'
+  show (Num n) = show n
 
-solve2 = undefined
+parse :: String -> [ℜ]
+parse s = zip [0..] (trim s) >>= \(i,a) -> replicate (read [a]) (if even i then Num (i `div` 2) else None)
+
+sort1 :: [ℜ] -> [ℜ]
+sort1 s
+  | None `notElem` s = s
+  | otherwise = case last s of
+                  None -> sort1 $ init s
+                  n    -> sort1 $ takeWhile (/= None) s ++ [n] ++ drop 1 (dropWhile (/= None) (init s))
+
+sort2 :: [ℜ] -> [ℜ]
+sort2 = undefined
+
+solve :: ([ℜ] -> [ℜ]) -> [ℜ] -> Int
+solve f s = let fixed = (\(Num n) -> n) <$> f s in
+  sum $ zipWith (*) fixed [0..]
 
 main :: IO ()
-main = readFile "inputs/9" <&> parse >>= \i ->
+main = readFile "inputs/9.example" <&> parse >>= \i ->
-       print (solve1 i) >>
+       print (solve sort1 i) >>
-       print (solve2 i)
+       print (solve sort2 i)