feat: Set project up and implement day1 part1

day1/Main.hs

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+module Main where
+
+import System.Environment (getArgs)
+import System.IO (Handle, hIsEOF, hGetLine, withFile, IOMode(ReadMode))
+import Text.Read (readMaybe)
+
+import Data.List (sort)
+import Data.Char (isDigit, isSpace)
+
+mapSnd :: (b -> c) -> (a, b) -> (a, c)
+mapSnd f (a, b) = (a, f b)
+
+parseLine :: String -> IO (Int, Int)
+parseLine line = let (l, (_, r)) = (mapSnd (span isSpace). span isDigit) line
+                 in
+                    case readMaybe l >>= \l' -> readMaybe r
+                                     >>= \r' -> return (l', r') of
+                        Just a -> return a
+                        Nothing -> fail "Input file is incorrectly formatted"
+
+readLists :: Handle -> IO ([Int], [Int])
+readLists h = do
+                  shouldStop <- hIsEOF h
+                  if shouldStop
+                      then return ([], [])
+                      else do
+                          line <- hGetLine h
+                          (l, r) <- parseLine line
+                          (ls, rs) <- readLists h
+                          return (l:ls, r:rs)
+
+computeDistance :: [Int] -> [Int] -> Int
+computeDistance l r = sum (zipWith (curry (abs . uncurry (-))) l r)
+
+main :: IO ()
+main = do
+    args <- getArgs
+    (fp:_) <- return args
+    (l, r) <- withFile fp ReadMode readLists
+
+    putStrLn ("Solution (Part 1) : " ++ show (computeDistance (sort l) (sort r)))

day1/test_input

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+3   4
+4   3
+2   5
+1   3
+3   9
+3   3