Enter.hs

{-# LANGUAGE CPP                    #-}
{-# LANGUAGE DeriveDataTypeable     #-}
{-# LANGUAGE FlexibleInstances      #-}
{-# LANGUAGE FunctionalDependencies #-}
{-# LANGUAGE MultiParamTypeClasses  #-}
{-# LANGUAGE RankNTypes             #-}
{-# LANGUAGE ScopedTypeVariables    #-}
{-# LANGUAGE TypeFamilies           #-}
{-# LANGUAGE TypeOperators          #-}
{-# LANGUAGE UndecidableInstances   #-}
module Servant.Server.Internal.Enter where

#if !MIN_VERSION_base(4,8,0)
import           Control.Applicative
#endif
import qualified Control.Category            as C
#if MIN_VERSION_mtl(2,2,1)
import           Control.Monad.Except
#endif
import           Control.Monad.Identity
import           Control.Monad.Morph
import           Control.Monad.Reader
import qualified Control.Monad.State.Lazy    as LState
import qualified Control.Monad.State.Strict  as SState
#if MIN_VERSION_mtl(2,2,1)
import           Control.Monad.Trans.Either
#endif
import qualified Control.Monad.Writer.Lazy   as LWriter
import qualified Control.Monad.Writer.Strict as SWriter
import           Data.Typeable
import           Servant.API

class Enter typ arg ret | typ arg -> ret, typ ret -> arg where
    enter :: arg -> typ -> ret

-- **  Servant combinators
instance ( Enter typ1 arg1 ret1, Enter typ2 arg2 ret2
         , arg1 ~ arg2
         ) => Enter (typ1 :<|> typ2) arg1 (ret1 :<|> ret2) where
    enter e (a :<|> b) = enter e a :<|> enter e b

instance (Enter b arg ret) => Enter (a -> b) arg (a -> ret) where
    enter arg f a = enter arg (f a)

-- ** Useful instances

-- | A natural transformation from @m@ to @n@. Used to `enter` particular
-- datatypes.
newtype m :~> n = Nat { unNat :: forall a. m a -> n a} deriving Typeable

instance C.Category (:~>) where
    id = Nat id
    Nat f . Nat g = Nat (f . g)

instance Enter (Raw m a) (m :~> n) (Raw n a) where
    enter _ (Raw a) = Raw a

instance Enter (m a) (m :~> n) (n a) where
    enter (Nat f) = f

-- | Like `lift`.
liftNat :: (Control.Monad.Morph.MonadTrans t, Monad m) => m :~> t m
liftNat = Nat Control.Monad.Morph.lift

runReaderTNat :: r -> (ReaderT r m :~> m)
runReaderTNat a = Nat (`runReaderT` a)

evalStateTLNat :: Monad m => s -> (LState.StateT s m :~> m)
evalStateTLNat a = Nat (`LState.evalStateT` a)

evalStateTSNat :: Monad m => s -> (SState.StateT s m :~> m)
evalStateTSNat a = Nat (`SState.evalStateT` a)

-- | Log the contents of `SWriter.WriterT` with the function provided as the
-- first argument, and return the value of the @WriterT@ computation
logWriterTSNat :: MonadIO m => (w -> IO ()) -> (SWriter.WriterT w m :~> m)
logWriterTSNat logger = Nat $ \x -> do
    (a, w) <- SWriter.runWriterT x
    liftIO $ logger w
    return a

-- | Like `logWriterTSNat`, but for strict @WriterT@.
logWriterTLNat :: MonadIO m => (w -> IO ()) -> (LWriter.WriterT w m :~> m)
logWriterTLNat logger = Nat $ \x -> do
    (a, w) <- LWriter.runWriterT x
    liftIO $ logger w
    return a

#if MIN_VERSION_mtl(2,2,1)
fromExceptT :: ExceptT e m :~> EitherT e m
fromExceptT = Nat $ \x -> EitherT $ runExceptT x
#endif

-- | Like @mmorph@'s `hoist`.
hoistNat :: (MFunctor t, Monad m) => (m :~> n) ->  (t m :~> t n)
hoistNat (Nat n) = Nat $ hoist n

-- | Like @mmorph@'s `embed`.
embedNat :: (MMonad t, Monad n) => (m :~> t n) -> (t m :~> t n)
embedNat (Nat n) = Nat $ embed n

-- | Like @mmorph@'s `squash`.
squashNat :: (Monad m, MMonad t) => t (t m) :~> t m
squashNat = Nat squash

-- | Like @mmorph@'s `generalize`.
generalizeNat :: Applicative m => Identity :~> m
generalizeNat = Nat (pure . runIdentity)

Error

src/Servant/Server/Internal/Enter.hs:55:10:
    Functional dependencies conflict between instance declarations:
      instance Enter (Raw m a) (m :~> n) (Raw n a)
        -- Defined at src/Servant/Server/Internal/Enter.hs:55:10
      instance Enter (m a) (m :~> n) (n a)
        -- Defined at src/Servant/Server/Internal/Enter.hs:58:10

Raw.hs

{-# LANGUAGE DeriveDataTypeable #-}
{-# LANGUAGE KindSignatures #-}
{-# OPTIONS_HADDOCK not-home    #-}
module Servant.API.Raw where

import Data.Typeable (Typeable)
-- | Endpoint for plugging in your own Wai 'Application's.
--
-- The given 'Application' will get the request as received by the server, potentially with
-- a modified (stripped) 'pathInfo' if the 'Application' is being routed with 'Servant.API.Sub.:>'.
--
-- In addition to just letting you plug in your existing WAI 'Application's,
-- this can also be used with 'Servant.Utils.StaticFiles.serveDirectory' to serve
-- static files stored in a particular directory on your filesystem
newtype Raw (m :: * -> *) a = Raw {
  unRaw :: a
  }
  deriving (Eq, Show, Typeable)