[hs] Add day module

To help with reading input etc. for a single day

hs/package.yaml

@@ -4,6 +4,7 @@ version:             0.1.0.0
 dependencies:
 - base >= 4.7 && < 5
 - containers
+- megaparsec
 - optparse-applicative
 - text
 

hs/src/Aoc/Day.hs

@@ -0,0 +1,41 @@
+module Aoc.Day
+  ( Day(..)
+  , dayPure
+  , dayFile
+  , dayString
+  , dayText
+  , Parser
+  , dayParser
+  ) where
+
+import           Control.Monad
+import           Data.Void
+
+import qualified Data.Text       as T
+import qualified Data.Text.IO    as T
+import           Text.Megaparsec
+
+data Day
+  = DayPure String (IO ())
+  | DayFile String (FilePath -> IO ())
+
+dayPure :: String -> IO () -> Day
+dayPure = DayPure
+
+dayFile :: String -> (FilePath -> IO ()) -> Day
+dayFile = DayFile
+
+dayString :: String -> (String -> IO ()) -> Day
+dayString name f = dayFile name $ f <=< readFile
+
+dayText :: String -> (T.Text -> IO ()) -> Day
+dayText name f = dayFile name $ f <=< T.readFile
+
+type Parser = Parsec Void T.Text
+
+dayParser :: String -> Parser a -> (a -> IO ()) -> Day
+dayParser name p f = dayFile name $ \path -> do
+  text <- T.readFile path
+  case parse p path text of
+    Right a -> f a
+    Left e  -> putStrLn $ errorBundlePretty e