diff --git a/Control/ContStuff.hs b/Control/ContStuff.hs
--- a/Control/ContStuff.hs
+++ b/Control/ContStuff.hs
@@ -99,7 +99,10 @@
 instance MonadFix Id where
   mfix f = fix (f . getId)
 
+instance Show a => Show (Id a) where
+  show x = "Id " ++ show x
 
+
 -- ================== --
 -- Monad transformers --
 -- ================== --
@@ -120,6 +123,9 @@
                 -> (i -> m r)
                 -> m r }
 
+instance Applicative m => Abortable (ChoiceT r i m) where
+  type Result (ChoiceT r i m) = r
+  abort x = ChoiceT $ \_ _ _ -> pure x
 
 instance Alternative (ChoiceT r i m) where
   empty = ChoiceT $ \_ z k -> k z
@@ -721,35 +727,36 @@
 
 -- | Monads, which support lifting base monad computations.
 
-class LiftBase m a where
+class LiftBase m where
   -- | Base monad of @m@.
-  type Base m a
+  type Base m :: * -> *
 
   -- | Promote a base monad computation.
   base :: Base m a -> m a
 
-instance LiftBase IO a where type Base IO a = IO a; base = id
-instance LiftBase Id a where type Base Id a = Id a; base = id
-instance LiftBase Maybe a where type Base Maybe a = Maybe a; base = id
-instance LiftBase (ST s) a where type Base (ST s) a = ST s a; base = id
-instance LiftBase [] a where type Base [] a = [a]; base = id
-instance LiftBase ((->) r) a where type Base ((->) r) a = r -> a; base = id
 
-instance (LiftBase m a, Monad m) => LiftBase (IdT m) a where
-  type Base (IdT m) a = Base m a; base = lift . base
-instance (LiftBase m a, Monad m) => LiftBase (ChoiceT r i m) a where
-  type Base (ChoiceT r i m) a = Base m a; base = lift . base
-instance (LiftBase m a, Monad m) => LiftBase (ContT r m) a where
-  type Base (ContT r m) a = Base m a; base = lift . base
-instance (LiftBase m a, Monad m) => LiftBase (EitherT r e m) a where
-  type Base (EitherT r e m) a = Base m a; base = lift . base
-instance (LiftBase m a, Monad m) => LiftBase (StateT r s m) a where
-  type Base (StateT r s m) a = Base m a; base = lift . base
+instance LiftBase IO where type Base IO = IO; base = id
+instance LiftBase Id where type Base Id = Id; base = id
+instance LiftBase Maybe where type Base Maybe = Maybe; base = id
+instance LiftBase (ST s) where type Base (ST s) = ST s; base = id
+instance LiftBase [] where type Base [] = []; base = id
+instance LiftBase ((->) r) where type Base ((->) r) = (->) r; base = id
 
+instance (LiftBase m, Monad m) => LiftBase (IdT m) where
+  type Base (IdT m) = Base m; base = lift . base
+instance (LiftBase m, Monad m) => LiftBase (ChoiceT r i m) where
+  type Base (ChoiceT r i m) = Base m; base = lift . base
+instance (LiftBase m, Monad m) => LiftBase (ContT r m) where
+  type Base (ContT r m) = Base m; base = lift . base
+instance (LiftBase m, Monad m) => LiftBase (EitherT r e m) where
+  type Base (EitherT r e m) = Base m; base = lift . base
+instance (LiftBase m, Monad m) => LiftBase (StateT r s m) where
+  type Base (StateT r s m) = Base m; base = lift . base
 
--- | Handy alias for lifting IO computations.
 
-io :: (LiftBase m a, Base m a ~ IO a) => Base m a -> m a
+-- | Handy alias for lifting 'IO' computations.
+
+io :: (LiftBase m, Base m ~ IO) => Base m a -> m a
 io = base
 
 
diff --git a/contstuff.cabal b/contstuff.cabal
--- a/contstuff.cabal
+++ b/contstuff.cabal
@@ -1,5 +1,5 @@
 Name:          contstuff
-Version:       0.4.0
+Version:       0.4.1
 Category:      Control, Monads
 Synopsis:      Easy to use CPS-based monads
 Maintainer:    Ertugrul Söylemez <es@ertes.de>