From 7882899b21a02f5ebcc73dd64988be9841577d06 Mon Sep 17 00:00:00 2001
From: David Johnson <djohnson.m@gmail.com>
Date: Thu, 17 Nov 2016 15:27:41 -0600
Subject: [PATCH] Initial commit of Lift datatype

---
 servant/src/Servant/Utils/Enter.hs | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/servant/src/Servant/Utils/Enter.hs b/servant/src/Servant/Utils/Enter.hs
index 12f7a530..505e7ef3 100644
--- a/servant/src/Servant/Utils/Enter.hs
+++ b/servant/src/Servant/Utils/Enter.hs
@@ -49,6 +49,13 @@ instance C.Category (:~>) where
 instance Enter (m a) (m :~> n) (n a) where
     enter (Nat f) = f
 
+-- | A lifting function from @a@ to @n a@. Used to `enter` particular
+-- datatypes.
+newtype x :^ n = Lift { unLift :: forall a. a -> n a} deriving Typeable
+
+instance Enter a (a :^ n) (n a) where
+    enter (Lift f) = f
+
 -- | Like `lift`.
 liftNat :: (Control.Monad.Morph.MonadTrans t, Monad m) => m :~> t m
 liftNat = Nat Control.Monad.Morph.lift