Quest 1: Whispers in the Shell

Ooh, challenges! Here we go!

I haven't really written any Haskell since last year's AoC, and boy am I rusty.

import Control.Monad  
import Data.List  
import Data.List.Split  
import Data.Vector qualified as V  

readInput s =  
  let [names, _, moves] = splitOn "," <$> lines s  
   in (names, map readMove moves)  
  where  
    readMove (d : s) =  
      let n = read s :: Int  
       in case d of  
            'L' -> -n  
            'R' -> n  

addWith f = (f .) . (+)  

part1 names moves =  
  names !! foldl' (addWith $ clamp (length names)) 0 moves  
  where  
    clamp n x  
      | x < 0 = 0  
      | x >= n = n - 1  
      | otherwise = x  

part2 names moves =  names !! (sum moves `mod` length names)  

part3 names moves =  
  V.head  
    . foldl' exchange (V.fromList names)  
    $ map (`mod` length names) moves  
  where  
    exchange v k = v V.// [(0, v V.! k), (k, V.head v)]  

main =  
  forM_  
    [ ("everybody_codes_e2025_q01_p1.txt", part1),  
      ("everybody_codes_e2025_q01_p2.txt", part2),  
      ("everybody_codes_e2025_q01_p3.txt", part3)  
    ]  
    $ \(input, solve) ->  
      readFile input >>= putStrLn . uncurry solve . readInput