Solve day 3, part 2

src/Day3.hs

@@ -59,7 +59,13 @@ parseGrid s =
 day3 :: IO ()
 day3 = do
   r <- readFile "./input/day3"
+  let grid = parseGrid r
   putStr "[Day 3-1] # trees: "
-  case slideDown (0, 0) (3, 1) (parseGrid r) (Just []) of
+  case slideDown (0, 0) (3, 1) grid (Just []) of
     Nothing -> putStrLn "ERROR"
-    Just locs -> print . countTrees $ locs
+    Just locs -> print . countTrees $ locs
+  putStr "[Day 3-2] # trees: "
+  let mTrees = mapM (\x -> slideDown (0, 0) x grid (Just [])) [(1, 1), (3, 1), (5, 1), (7, 1), (1, 2)]
+  case mTrees of
+    Nothing -> putStrLn "ERROR"
+    Just trees -> print . product $ map countTrees trees