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Initial commit of Lift datatype

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This commit is contained in:
David Johnson 2016-11-17 15:27:41 -06:00
parent 4fd31a60fb
commit 7882899b21
1 changed files with 7 additions and 0 deletions
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7
servant/src/Servant/Utils/Enter.hs
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@ -49,6 +49,13 @@ instance C.Category (:~>) where
instance Enter (m a) (m :~> n) (n a) where instance Enter (m a) (m :~> n) (n a) where
enter (Nat f) = f 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`. -- | Like `lift`.
liftNat :: (Control.Monad.Morph.MonadTrans t, Monad m) => m :~> t m liftNat :: (Control.Monad.Morph.MonadTrans t, Monad m) => m :~> t m
liftNat = Nat Control.Monad.Morph.lift liftNat = Nat Control.Monad.Morph.lift