2023-01 in haskell

1 files changed, 44 insertions, 0 deletions

diff --git a/2023/1-Trebuchet/first.hs b/2023/1-Trebuchet/first.hs
new file mode 100644
index 0000000..366d28e
--- /dev/null
+++ b/2023/1-Trebuchet/first.hs
@@ -0,0 +1,44 @@
+-- requires cabal install --lib megaparsec parser-combinators
+module Main (main) where
+import Control.Monad (void, when)
+import Data.Char qualified as C
+import Data.List qualified as L
+import Data.Map qualified as M
+import Data.Maybe
+import Data.Set qualified as S
+import Data.Void (Void)
+import Text.Megaparsec
+import Text.Megaparsec.Char
+
+exampleExpectedOutput = 142
+
+type Input = [String]
+
+type Parser = Parsec Void String
+
+parseInput' :: Parser Input
+parseInput' = some (some alphaNumChar <* eol) <* eof
+
+parseInput :: String -> IO Input
+parseInput filename = do
+  input <- readFile filename
+  case runParser parseInput' filename input of
+    Left bundle -> error $ errorBundlePretty bundle
+    Right input' -> return input'
+
+process :: Int -> String -> Int
+process acc str = acc + f * 10 + l
+  where
+    f = C.digitToInt . head $ dropWhile C.isLetter str
+    l = C.digitToInt . head . dropWhile C.isLetter $ reverse str
+
+compute :: Input -> Int
+compute = L.foldl' process 0
+
+main :: IO ()
+main = do
+  example <- parseInput "example"
+  let exampleOutput = compute example
+  when  (exampleOutput /= exampleExpectedOutput)  (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
+  input <- parseInput "input"
+  print $ compute input