added missing MonadTrans instance for ListT

Author: jdegoes

README.md

@@ -25,6 +25,8 @@
 
     instance monadListT :: (Monad f) => Monad (ListT f)
 
+    instance monadTransListT :: MonadTrans ListT
+
     instance monoidListT :: (Applicative f) => Monoid (ListT f a)
 
     instance semigroupListT :: (Applicative f) => Semigroup (ListT f a)

src/Control/Monad/ListT.purs

@@ -95,6 +95,9 @@ module Control.Monad.ListT
 
   instance monadListT :: (Monad f) => Monad (ListT f)
 
+  instance monadTransListT :: MonadTrans ListT where
+    lift = fromEffect
+
   singleton :: forall f a. (Applicative f) => a -> ListT f a
   singleton a = prepend a nil