diff --git a/haskell/Pre.hs b/haskell/Pre.hs
index 0350f6f..c55e865 100644
--- a/haskell/Pre.hs
+++ b/haskell/Pre.hs
@@ -70,7 +70,7 @@ import Data.Foldable1
 import Data.Function
 import Data.Functor
 import Data.List (sortOn, transpose)
-import Data.List.Extra (dropEnd, enumerate, notNull, splitOn)
+import Data.List.Extra (dropEnd, enumerate, firstJust, notNull, splitOn)
 import Data.List.NonEmpty (NonEmpty ((:|)), nonEmpty, some1, tail, tails)
 import Data.Maybe
 import Data.Ord
diff --git a/haskell/Puzzles/Day10.hs b/haskell/Puzzles/Day10.hs
index 659f662..e57cf35 100644
--- a/haskell/Puzzles/Day10.hs
+++ b/haskell/Puzzles/Day10.hs
@@ -2,14 +2,49 @@ module Puzzles.Day10 (puzzle) where
 
 import Pre
 
+import Data.IntMap qualified as IM
+
 puzzle :: Puzzle
 puzzle =
     Puzzle
         { number = 10
-        , parser = mempty
+        , parser = const $ flip sepEndBy newline do
+            void $ single '['
+            lights <- some $ (single '.' $> Off) <|> (single '#' $> On)
+            void $ single ']'
+            void space1
+            switches <- flip sepEndBy space1 do
+                void $ single '('
+                r <- Switch <$> decimal `sepBy` single ','
+                void $ single ')'
+                pure r
+            void $ single '{'
+            void $ decimal @_ @_ @_ @Int `sepBy` single ','
+            void $ single '}'
+            pure (Lights $ IM.fromList $ zip [0 ..] lights, switches)
         , parts =
-            [ \() ->
-                ()
+            [ sum . map \(lights, switches) ->
+                maybe (error "no solution") length
+                    . firstJust (firstJust (\(s, ls) -> guard (allOff ls) $> s))
+                    $ flip iterate [([], lights)] \ls ->
+                        concatMap (\s -> map (\(ss, l) -> (s : ss, applySwitch s l)) ls) switches
             ]
         , extraTests = mempty
         }
+
+data Light = On | Off
+    deriving (Eq, Ord, Show)
+flipLight :: Light -> Light
+flipLight = \case
+    On -> Off
+    Off -> On
+
+newtype Lights = Lights (IM.IntMap Light)
+    deriving (Eq, Ord, Show)
+allOff :: Lights -> Bool
+allOff (Lights ls) = all (== Off) $ map snd $ IM.toList ls
+
+newtype Switch = Switch [Int]
+    deriving (Eq, Ord, Show)
+applySwitch :: Switch -> Lights -> Lights
+applySwitch (Switch ss) (Lights ls) = Lights $ foldl' (flip $ IM.adjust flipLight) ls ss
diff --git a/outputs/real/10/1 b/outputs/real/10/1
new file mode 100644
index 0000000..8410b8b
--- /dev/null
+++ b/outputs/real/10/1
@@ -0,0 +1 @@
+473