Add applyNT

src/Control/Natural.hs

@@ -25,6 +25,8 @@ module Control.Natural
   , type (~>)
     -- * Conversion functions between the newtype and the synonym
   , unwrapNT
+    -- * Type inference helper
+  , applyNT
     -- * Class for Natural Transformations
   , Transformation(..)
   ) where
@@ -84,3 +86,9 @@ instance Transformation f g (f :~> g) where
 --   transformation wrappers, including ':~>'.
 unwrapNT :: Transformation f g t => t -> (forall a . f a -> g a)
 unwrapNT = (#)
+
+-- | An alias to 'id', to help type-inference.
+--
+-- See <https://github.com/ku-fpg/natural-transformation/issues/9#issuecomment-172121060 comment on GitHub>
+applyNT :: (f ~> g) -> (f ~> g)
+applyNT nt = nt