Re-add first solution from temporary aoc repo

hs/app/Main.hs

@@ -1,6 +1,28 @@
 module Main where
 
-import Lib
+import Options.Applicative
+
+import Aoc.Y2019.A01
+
+data Settings = Settings
+  { function :: FilePath -> IO ()
+  , filename :: FilePath
+  }
+
+solutions :: Parser (FilePath -> IO ())
+solutions = subparser $ mconcat $ map (\(name, func) -> command name (info (pure func) mempty))
+  [ ("201901", solve201901)
+  ]
+
+parser :: Parser Settings
+parser = Settings
+  <$> solutions
+  <*> strArgument (metavar "INPUTFILE")
+
+opts :: ParserInfo Settings
+opts = info (helper <*> parser) $ fullDesc <> failureCode 1
 
 main :: IO ()
-main = someFunc
+main = do
+  settings <- execParser opts
+  function settings $ filename settings

hs/package.yaml

@@ -21,6 +21,7 @@ description:         Please see the README on GitHub at <https://github.com/gith
 
 dependencies:
 - base >= 4.7 && < 5
+- optparse-applicative
 
 library:
   source-dirs: src

hs/src/Aoc/Y2019/A01.hs

@@ -0,0 +1,19 @@
+module Aoc.Y2019.A01
+  ( solve201901
+  ) where
+
+fuel :: Integer -> Integer
+fuel n = (n `div` 3) - 2
+
+iteratedFuel :: Integer -> Integer
+iteratedFuel = sum . takeWhile (> 0) . tail . iterate fuel
+
+solve201901 :: FilePath -> IO ()
+solve201901 f = do
+  values <- (map read . lines) <$> readFile f
+
+  putStr "Total fuel: "
+  print $ sum $ map fuel values
+
+  putStr "Total fuel (iterated): "
+  print $ sum $ map iteratedFuel values

hs/src/Lib.hs

@@ -1,6 +0,0 @@
-module Lib
-    ( someFunc
-    ) where
-
-someFunc :: IO ()
-someFunc = putStrLn "someFunc"