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