diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,8 @@
+1.1
+----
+* Removed `HProfunctor`, `(..-)`, `invokeOnSTM`, `newSTM`, `snapshot`
+* Added `(?-)`
+
 1.0.5
 ----
 * Added `filterO` and `filteredO`
diff --git a/objective.cabal b/objective.cabal
--- a/objective.cabal
+++ b/objective.cabal
@@ -1,5 +1,5 @@
 name:                objective
-version:             1.0.5
+version:             1.1
 synopsis:            Composable objects
 description:         Composable objects
 homepage:            https://github.com/fumieval/objective
@@ -41,8 +41,6 @@
     , profunctors
     , void
     , witherable >= 0.1.3
-    , stm
-    , monad-stm
     , monad-skeleton >= 0.1.1 && <0.3
     , template-haskell
   ghc-options: -Wall
diff --git a/src/Control/Object.hs b/src/Control/Object.hs
--- a/src/Control/Object.hs
+++ b/src/Control/Object.hs
@@ -1,4 +1,3 @@
-{-# LANGUAGE Safe #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Control.Object
diff --git a/src/Control/Object/Instance.hs b/src/Control/Object/Instance.hs
--- a/src/Control/Object/Instance.hs
+++ b/src/Control/Object/Instance.hs
@@ -1,5 +1,4 @@
-{-# LANGUAGE Safe #-}
-{-# LANGUAGE GADTs, Rank2Types #-}
+{-# LANGUAGE GADTs, Rank2Types, LambdaCase #-}
 -----------------------------------------------------------------------------
 -- |
 -- Module      :  Control.Object.Instance
@@ -13,84 +12,53 @@
 -----------------------------------------------------------------------------
 module Control.Object.Instance (
   -- * Instantiation
-  Instance(..)
+  Instance
   , new
   , newSettle
-  , newSTM
   -- * Invocation
   , invokeOn
-  , invokeOnSTM
   , (.-)
-  , (..-)
-  , snapshot
+  , (?-)
   ) where
-import Control.Concurrent.STM.TMVar
-import Control.Monad.STM
+import Control.Concurrent
+import Control.Exception (evaluate)
 import Control.Object.Object
 import Control.Monad.IO.Class
-import Control.Monad.STM.Class
-import Control.Monad
-import Control.Monad.Catch (MonadMask, bracketOnError)
-
--- | TMVar-based instance
-data Instance f g where
-  InstRef :: (forall x. e x -> f x) -> (forall x. g x -> h x) -> TMVar (Object f g) -> Instance e h
+import Control.Monad.Catch
 
-instance HProfunctor Instance where
-  f ^>>@ InstRef l r v = InstRef (l . f) r v
-  {-# INLINE (^>>@) #-}
-  InstRef l r v @>>^ f = InstRef l (f . r) v
-  {-# INLINE (@>>^) #-}
+type Instance f g = MVar (Object f g)
 
 -- | Invoke a method with an explicit landing function.
+-- In case of exception, the original object will be set.
 invokeOn :: (MonadIO m, MonadMask m)
-         => (forall x. g x -> m x) -> Instance f g -> f a -> m a
-invokeOn m (InstRef t l v) f = bracketOnError
-  (liftIO $ atomically $ takeTMVar v)
-  (\obj -> liftIO $ atomically $ do
-    _ <- tryTakeTMVar v
-    putTMVar v obj)
-  (\obj -> do
-    (a, obj') <- m $ l $ runObject obj (t f)
-    liftIO $ atomically $ putTMVar v obj'
-    return a)
-
--- | Invoke a method with an explicit landing function.
-invokeOnSTM :: (forall x. g x -> STM x) -> Instance f g -> f a -> STM a
-invokeOnSTM m (InstRef t l v) f = do
-  obj <- takeTMVar v
-  (a, obj') <- m $ l $ runObject obj (t f)
-  putTMVar v obj'
+         => (forall x. g x -> m x) -> MVar (Object f g) -> f a -> m a
+invokeOn m v f = mask $ \restore -> do
+  obj <- liftIO $ takeMVar v
+  (a, obj') <- restore (m (runObject obj f) >>= liftIO . evaluate) `onException` liftIO (putMVar v obj)
+  liftIO $ putMVar v obj'
   return a
 
--- | Invoke a method, atomically.
-(..-) :: MonadSTM m => Instance f STM -> f a -> m a
-(..-) i = liftSTM . invokeOnSTM id i
-{-# INLINE (..-) #-}
-infixr 3 ..-
-
 -- | Invoke a method.
-(.-) :: (MonadIO m, MonadMask m) => Instance f m -> f a -> m a
+(.-) :: (MonadIO m, MonadMask m) => MVar (Object f m) -> f a -> m a
 (.-) = invokeOn id
 {-# INLINE (.-) #-}
 infixr 3 .-
 
--- | Take a snapshot of an instance.
-snapshot :: (MonadSTM m, Functor g) => Instance f g -> m (Object f g)
-snapshot (InstRef f g v) = liftSTM $ go `fmap` readTMVar v
-  where go (Object m) = Object $ fmap (fmap go) . g . m . f
+-- | Try to invoke a method. If the instance is unavailable, it returns Nothing.
+(?-) :: (MonadIO m, MonadMask m) => MVar (Object f m) -> f a -> m (Maybe a)
+v ?- f = mask $ \restore -> liftIO (tryTakeMVar v) >>= \case
+  Just obj -> do
+    (a, obj') <- restore (runObject obj f >>= liftIO . evaluate) `onException` liftIO (putMVar v obj)
+    liftIO $ putMVar v obj'
+    return (Just a)
+  Nothing -> return Nothing
 
 -- | Create a new instance. This can be used inside 'unsafePerformIO' to create top-level instances.
 new :: MonadIO m => Object f g -> m (Instance f g)
-new = liftIO . liftM (InstRef id id) . newTMVarIO
+new = liftIO . newMVar
 {-# INLINE new #-}
 
 -- | Create a new instance, having it sitting on the current environment.
 newSettle :: MonadIO m => Object f m -> m (Instance f m)
 newSettle = new
 {-# INLINE newSettle #-}
-
--- | Create a new instance.
-newSTM :: MonadSTM m => Object f g -> m (Instance f g)
-newSTM = liftSTM . liftM (InstRef id id) . newTMVar
-{-# INLINE newSTM #-}
diff --git a/src/Control/Object/Object.hs b/src/Control/Object/Object.hs
--- a/src/Control/Object/Object.hs
+++ b/src/Control/Object/Object.hs
@@ -23,7 +23,8 @@
   , (@>>@)
   , (@<<@)
   , liftO
-  , HProfunctor(..)
+  , (^>>@)
+  , (@>>^)
   , (@||@)
   -- * Stateful construction
   , unfoldO
@@ -96,16 +97,13 @@
 infixr 1 ^>>@
 infixr 1 @>>^
 
--- | Higher-order profunctors
-class HProfunctor k where
-  (^>>@) :: Functor h => (forall x. f x -> g x) -> k g h -> k f h
-  (@>>^) :: Functor h => k f g -> (forall x. g x -> h x) -> k f h
+(^>>@) :: Functor h => (forall x. f x -> g x) -> Object g h -> Object f h
+f ^>>@ m0 = go m0 where go (Object m) = Object $ fmap (fmap go) . m . f
+{-# INLINE (^>>@) #-}
 
-instance HProfunctor Object where
-  m0 @>>^ g = go m0 where go (Object m) = Object $ fmap (fmap go) . g . m
-  {-# INLINE (@>>^) #-}
-  f ^>>@ m0 = go m0 where go (Object m) = Object $ fmap (fmap go) . m . f
-  {-# INLINE (^>>@) #-}
+(@>>^) :: Functor h => Object f g -> (forall x. g x -> h x) -> Object f h
+m0 @>>^ g = go m0 where go (Object m) = Object $ fmap (fmap go) . g . m
+{-# INLINE (@>>^) #-}
 
 -- | The trivial object
 echo :: Functor f => Object f f
diff --git a/src/Data/Functor/Request.hs b/src/Data/Functor/Request.hs
--- a/src/Data/Functor/Request.hs
+++ b/src/Data/Functor/Request.hs
@@ -1,4 +1,3 @@
-{-# LANGUAGE Safe #-}
 {-# LANGUAGE CPP, DeriveFunctor, DeriveDataTypeable, ConstraintKinds, FlexibleContexts, TypeOperators, DataKinds, TypeFamilies #-}
 -----------------------------------------------------------------------------
 -- |