diff --git a/2021/day13.hs b/2021/day13.hs
new file mode 100644
index 0000000..04ed14d
--- /dev/null
+++ b/2021/day13.hs
@@ -0,0 +1,42 @@
+module Day13 where
+import Data.List.Split (splitOn)
+import Data.List (nub, sort)
+import Debug.Trace (trace)
+
+type Dot = (Int,Int)
+data Fold = Vertical Int | Horizontal Int deriving Show
+
+parse :: String -> Dot
+parse s = (read x, read y) where [x,y] = splitOn "," s
+
+parseFold :: String -> Fold
+parseFold s = if axis == "x" then Horizontal (read line) else Vertical (read line) where [axis,line] = splitOn "=" $ last (words s)
+
+fold :: Fold -> Dot -> Dot
+fold fold@(Vertical f)   (x,y) = (x, if y > f then f - (y-f) else y)
+fold fold@(Horizontal f) (x,y) = (if x > f then f - (x-f) else x, y)
+
+main :: IO ()
+main = do
+    input <- lines <$> getContents
+    let [dots',folds'] = splitOn [""] input
+    let dots = nub $ map parse dots'
+    let folds = map parseFold folds'
+
+    putStr "part 1: "
+    let dots1 = nub $ sort $ map (fold (head folds)) dots
+    print $ length dots1
+
+    putStr "part 2: "
+    let dots2 = nub $ sort $ map (\d -> foldl (flip fold) d folds) dots
+    print dots2
+    let min_x = minimum $ map fst dots2
+    let max_x = maximum $ map fst dots2
+    let min_y = minimum $ map snd dots2
+    let max_y = maximum $ map snd dots2
+    mapM_ (\y -> do
+            mapM_ (\x -> putChar (if (x,y) `elem` dots2 then '#' else '.')) [0..max_x]
+            putStrLn ""
+        ) [0..max_y]
+    -- print dots2
+    -- print $ length dots2