diff --git a/deferred-folds.cabal b/deferred-folds.cabal
--- a/deferred-folds.cabal
+++ b/deferred-folds.cabal
@@ -1,7 +1,7 @@
 name:
   deferred-folds
 version:
-  0.6.7
+  0.6.8
 category:
   Folding
 synopsis:
diff --git a/library/DeferredFolds/UnfoldM.hs b/library/DeferredFolds/UnfoldM.hs
--- a/library/DeferredFolds/UnfoldM.hs
+++ b/library/DeferredFolds/UnfoldM.hs
@@ -68,6 +68,7 @@
 instance Show a => Show (UnfoldM Identity a) where
   show = show . toList
 
+{-| Check whether it's empty -}
 {-# INLINE null #-}
 null :: Monad m => UnfoldM m input -> m Bool
 null (UnfoldM run) = run (\ _ _ -> return False) True
@@ -142,3 +143,9 @@
 tVarValue var = UnfoldM $ \ step state -> do
   a <- readTVar var
   step state a
+
+{-| Change the base monad using invariant natural transformations -}
+{-# INLINE hoist #-}
+hoist :: (forall a. m a -> n a) -> (forall a. n a -> m a) -> UnfoldM m a -> UnfoldM n a
+hoist trans1 trans2 (UnfoldM unfold) = UnfoldM $ \ step init -> 
+  trans1 (unfold (\ a b -> trans2 (step a b)) init)