Make liftF a method of MonadFree

This seems to work a bit better for things like `FT`.

src/Control/Monad/Free.hs

@@ -30,7 +30,6 @@ module Control.Monad.Free
   ( MonadFree(..)
   , Free(..)
   , retract
-  , liftF
   , iter
   , iterA
   , iterM

src/Control/Monad/Free/Church.hs

@@ -63,7 +63,6 @@ module Control.Monad.Free.Church
   , hoistF
   , foldF
   , MonadFree(..)
-  , liftF
   , cutoff
   ) where
 
@@ -157,6 +156,7 @@ instance MonadTrans F where
 
 instance Functor f => MonadFree f (F f) where
   wrap f = F (\kp kf -> kf (fmap (\ (F m) -> m kp kf) f))
+  liftF f = F (\kp kf -> kf (fmap kp f))
 
 instance MonadState s m => MonadState s (F m) where
   get = lift get

src/Control/Monad/Free/Class.hs

@@ -26,8 +26,8 @@
 ----------------------------------------------------------------------------
 module Control.Monad.Free.Class
   ( MonadFree(..)
-  , liftF
   , wrapT
+  , defaultWrap
   ) where
 
 import Control.Monad
@@ -109,6 +109,10 @@ class Monad m => MonadFree f m | m -> f where
   wrap = join . lift . wrap . fmap return
 #endif
 
+  -- | A version of lift that can be used with just a Functor for f.
+  liftF :: Functor f => f a -> m a
+  liftF = wrap . fmap return
+
 instance (Functor f, MonadFree f m) => MonadFree f (ReaderT e m) where
   wrap fm = ReaderT $ \e -> wrap $ flip runReaderT e <$> fm
 
@@ -151,13 +155,13 @@ instance (Functor f, MonadFree f m) => MonadFree f (ExceptT e m) where
 -- instance (Functor f, MonadFree f m) => MonadFree f (EitherT e m) where
 --   wrap = EitherT . wrap . fmap runEitherT
 
--- | A version of lift that can be used with just a Functor for f.
-liftF :: (Functor f, MonadFree f m) => f a -> m a
-liftF = wrap . fmap return
-
 -- | A version of wrap for monad transformers over a free monad.
 --
 -- /Note:/ that this is the default implementation for 'wrap' for
 -- @MonadFree f (t m)@.
 wrapT :: (Functor f, MonadFree f m, MonadTrans t, Monad (t m)) => f (t m a) -> t m a
 wrapT = join . lift . liftF
+
+-- | An implementation of 'wrap' for 'MonadFree' instances that define 'liftF'.
+defaultWrap :: (Functor f, MonadFree f m) => f (m a) -> m a
+defaultWrap = join . liftF

src/Control/Monad/Trans/Free.hs

@@ -36,7 +36,6 @@ module Control.Monad.Trans.Free
   -- * The free monad
   , Free, free, runFree
   -- * Operations
-  , liftF
   , iterT
   , iterTM
   , hoistFreeT

src/Control/Monad/Trans/Free/Ap.hs

@@ -28,7 +28,6 @@ module Control.Monad.Trans.Free.Ap
   -- * The free monad
   , Free, free, runFree
   -- * Operations
-  , liftF
   , iterT
   , iterTM
   , hoistFreeT

src/Control/Monad/Trans/Free/Church.hs

@@ -44,7 +44,6 @@ module Control.Monad.Trans.Free.Church
   , iterM
   -- * Free Monads With Class
   , MonadFree(..)
-  , liftF
   ) where
 
 import Control.Applicative
@@ -122,6 +121,7 @@ instance Monad (FT f m) where
 
 instance MonadFree f (FT f m) where
   wrap f = FT (\kp kf -> kf (\ft -> runFT ft kp kf) f)
+  liftF f = FT (\kp kf -> kf kp f)
 
 instance MonadTrans (FT f) where
   lift m = FT (\a _ -> m >>= a)