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diff --git a/2023/15-Lens_Library/first.hs b/2023/15-Lens_Library/first.hs
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+-- requires cabal install --lib megaparsec parser-combinators split
+module Main (main) where
+
+import Control.Applicative.Permutations
+import Control.Monad (void, when)
+import Data.Char qualified as C
+import Data.Either
+import Data.Functor
+import Data.List qualified as L
+import Data.Map qualified as M
+import Data.Maybe
+import Data.Set qualified as S
+import Data.List.Split qualified as DLS
+import Data.Vector qualified as V
+import Data.Void (Void)
+import Text.Megaparsec
+import Text.Megaparsec.Char
+
+import Debug.Trace
+
+exampleExpectedOutput = 1320
+
+compute :: String -> Int
+compute input = sum $ map (hash 0) items
+  where
+    items :: [String]
+    items = DLS.endByOneOf ",\n" input
+    hash :: Int -> String -> Int
+    hash i [] = i
+    hash i (x:xs) = hash (((i + C.ord x) * 17) `rem` 256) xs
+
+main :: IO ()
+main = do
+  example <- readFile "example"
+  let exampleOutput = compute example
+  when  (exampleOutput /= exampleExpectedOutput)  (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
+  input <- readFile "input"
+  print $ compute input