Add Day 4, Puzzle 1 solution

src/Main.hs

@@ -3,6 +3,7 @@ module Main (main) where
 import Day01 (day01_1, day01_2)
 import Day02 (day02_1, day02_2)
 import Day03 (day03_1, day03_2)
+import Day04 (day04_1)
 import System.Environment (getArgs)
 
 main :: IO ()
@@ -24,6 +25,9 @@ main = do
     "3" : _ -> do
       day03_1
       day03_2
+    "4" : "1" : _ -> day04_1
+    "4" : _ -> do
+      day04_1
     "all" : _ -> do
       day01_1
       day01_2
@@ -31,4 +35,5 @@ main = do
       day02_2
       day03_1
       day03_2
+      day04_1
     _ -> error "Not implemented"