Enhanced the entry-point a bit

y2019/app/Main.hs

@@ -1,9 +1,6 @@
 module Main where
 
--- import Day1
-import Day2
-
--- TODO Day selection via args?
+import DayPicker
 
 main :: IO ()
-main = day2
+main = dayPicker

y2019/src/DayPicker.hs

@@ -0,0 +1,20 @@
+module DayPicker
+  ( dayPicker
+  )
+where
+
+import System.Environment
+
+import Day1
+import Day2
+
+load :: [String] -> IO ()
+load [] = putStrLn "Usage: script [day]"
+load ("1":_) = day1
+load ("2":_) = day2
+load _ = putStrLn "Unavailable date"
+
+dayPicker :: IO ()
+dayPicker = do
+  args <- getArgs
+  load args