Merge pull request #8 from ephemient/hs/day1

hs/aoc2024.cabal

@@ -39,7 +39,6 @@ executable aoc2024
         aoc2024,
         base ^>=4.20.0.0,
         filepath ^>=1.5.2.0,
-        megaparsec ^>=9.7.0,
         text ^>=2.1.1
     ghc-options:      -no-hs-main -threaded -Wall
     default-language: GHC2024

hs/app/Main.hs

@@ -9,7 +9,6 @@ import Data.Function (on)
 import Data.Maybe (fromMaybe)
 import Data.Text (Text)
 import qualified Data.Text.IO as TIO (putStrLn, readFile)
-import Text.Megaparsec (errorBundlePretty)
 import System.Environment (getArgs, lookupEnv)
 import System.FilePath (combine)
 
@@ -32,4 +31,4 @@ run' day name showIO funcs = do
 
 main :: IO ()
 main = do
-    run 1 print [Day1.part1, Day1.part2]
+    run 1 (either fail print) [Day1.part1, Day1.part2]

hs/src/Day1.hs

@@ -4,19 +4,27 @@ Description:    <https://adventofcode.com/2024/day/1 Day 1: Historian Hysteria>
 -}
 module Day1 (part1, part2) where
 
+import Common (readEntire)
 import Data.Function (on)
-import Data.IntMap (IntMap)
 import qualified Data.IntMap as IntMap (fromListWith, findWithDefault)
 import Data.List (sort, transpose)
 import Data.Text (Text)
-import qualified Data.Text as T (lines, words, unpack)
+import qualified Data.Text as T (lines, words)
+import qualified Data.Text.Read as T (decimal)
 
-part1 :: Text -> Int
-part1 input = sum $ abs <$> cs where
-    [as, bs] = transpose $ map (map (read . T.unpack) . T.words) $ T.lines input
-    cs = (zipWith (-) `on` sort) as bs
+parse :: Text -> Either String [[Int]]
+parse = fmap transpose . mapM (mapM (readEntire T.decimal) . T.words) . T.lines
 
-part2 :: Text -> Int
-part2 input = sum [a * IntMap.findWithDefault 0 a cs | a <- as] where
-    [as, bs] = transpose $ map (map (read . T.unpack) . T.words) $ T.lines input
-    cs = IntMap.fromListWith (+) [(b, 1) | b <- bs]
+part1 :: Text -> Either String Int
+part1 input = case parse input of
+    Left err -> Left err
+    Right [as, bs] -> pure $ sum $ abs <$> (zipWith (-) `on` sort) as bs
+    _ -> Left "no parse"
+
+part2 :: Text -> Either String Int
+part2 input = case parse input of
+    Left err -> Left err
+    Right [as, bs] ->
+        let cs = IntMap.fromListWith (($!) . (+)) [(b, 1) | b <- bs]
+        in pure $ sum [a * IntMap.findWithDefault 0 a cs | a <- as]
+    _ -> Left "no parse"

hs/test/Day1Spec.hs

@@ -20,7 +20,7 @@ spec :: Spec
 spec = do
     describe "part 1" $ do
         it "examples" $ do
-            part1 example `shouldBe` 11
+            part1 example `shouldBe` Right 11
     describe "part 2" $ do
         it "examples" $ do
-            part2 example `shouldBe` 31
+            part2 example `shouldBe` Right 31