servant/servant-client/src/Servant/Client/Generic.hs
2017-01-17 16:29:24 +03:00

158 lines
5.4 KiB
Haskell

{-# LANGUAGE DataKinds #-}
{-# LANGUAGE DefaultSignatures #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE TypeFamilies #-}
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE UndecidableInstances #-}
module Servant.Client.Generic
( ClientLike(..)
, genericMkClientL
, genericMkClientP
) where
import Generics.SOP (Code, Generic, I(..), NP(..), NS(Z), SOP(..), to)
import Servant.API ((:<|>)(..))
import Servant.Client (ClientM)
-- | This class allows us to match client structure with client functions
-- produced with 'client' without explicit pattern-matching.
--
-- The client structure needs a 'Generics.SOP.Generic' instance.
--
-- Example:
--
-- > type API
-- > = "foo" :> Capture "x" Int :> Get '[JSON] Int
-- > :<|> "bar" :> QueryParam "a" Char :> QueryParam "b" String :> Post '[JSON] [Int]
-- > :<|> Capture "nested" Int :> NestedAPI
-- >
-- > type NestedAPI
-- > = Get '[JSON] String
-- > :<|> "baz" :> QueryParam "c" Char :> Post '[JSON] ()
-- >
-- > data APIClient = APIClient
-- > { getFoo :: Int -> ClientM Int
-- > , postBar :: Maybe Char -> Maybe String -> ClientM [Int]
-- > , mkNestedClient :: Int -> NestedClient
-- > } deriving GHC.Generic
-- >
-- > instance Generics.SOP.Generic APIClient
-- > instance (Client API ~ client) => ClientLike client APIClient
-- >
-- > data NestedClient = NestedClient
-- > { getString :: ClientM String
-- > , postBaz :: Maybe Char -> ClientM ()
-- > } deriving GHC.Generic
-- >
-- > instance Generics.SOP.Generic NestedClient
-- > instance (Client NestedAPI ~ client) => ClientLike client NestedClient
-- >
-- > mkAPIClient :: APIClient
-- > mkAPIClient = mkClient (client (Proxy :: Proxy API))
--
-- By default, left-nested alternatives are expanded:
--
-- > type API1
-- > = "foo" :> Capture "x" Int :> Get '[JSON] Int
-- > :<|> "bar" :> QueryParam "a" Char :> Post '[JSON] String
-- >
-- > type API2
-- > = "baz" :> QueryParam "c" Char :> Post '[JSON] ()
-- >
-- > type API = API1 :<|> API2
-- >
-- > data APIClient = APIClient
-- > { getFoo :: Int -> ClientM Int
-- > , postBar :: Maybe Char -> ClientM String
-- > , postBaz :: Maybe Char -> ClientM ()
-- > } deriving GHC.Generic
-- >
-- > instance Generics.SOP.Generic APIClient
-- > instance (Client API ~ client) => ClientLike client APIClient
-- >
-- > mkAPIClient :: APIClient
-- > mkAPIClient = mkClient (client (Proxy :: Proxy API))
--
-- If you want to define client for @API1@ as a separate data structure,
-- you can use 'genericMkClientP':
--
-- > data APIClient1 = APIClient1
-- > { getFoo :: Int -> ClientM Int
-- > , postBar :: Maybe Char -> ClientM String
-- > } deriving GHC.Generic
-- >
-- > instance Generics.SOP.Generic APIClient1
-- > instance (Client API1 ~ client) => ClientLike client APIClient1
-- >
-- > data APIClient = APIClient
-- > { mkAPIClient1 :: APIClient1
-- > , postBaz :: Maybe Char -> ClientM ()
-- > } deriving GHC.Generic
-- >
-- > instance Generics.SOP.Generic APIClient
-- > instance (Client API ~ client) => ClientLike client APIClient where
-- > mkClient = genericMkClientP
-- >
-- > mkAPIClient :: APIClient
-- > mkAPIClient = mkClient (client (Proxy :: Proxy API))
class ClientLike client custom where
mkClient :: client -> custom
default mkClient :: (Generic custom, Code custom ~ '[xs], GClientList client '[], GClientLikeL (ClientList client '[]) xs)
=> client -> custom
mkClient = genericMkClientL
instance ClientLike client custom
=> ClientLike (a -> client) (a -> custom) where
mkClient c = mkClient . c
instance ClientLike (ClientM a) (ClientM a) where
mkClient = id
-- GClientLikeP
class GClientLikeP client xs where
gMkClientP :: client -> NP I xs
instance (GClientLikeP b (y ': xs), ClientLike a x)
=> GClientLikeP (a :<|> b) (x ': y ': xs) where
gMkClientP (a :<|> b) = I (mkClient a) :* gMkClientP b
instance ClientLike a x => GClientLikeP a '[x] where
gMkClientP a = I (mkClient a) :* Nil
-- GClientLikeL
class GClientLikeL (xs :: [*]) (ys :: [*]) where
gMkClientL :: NP I xs -> NP I ys
instance GClientLikeL '[] '[] where
gMkClientL Nil = Nil
instance (ClientLike x y, GClientLikeL xs ys) => GClientLikeL (x ': xs) (y ': ys) where
gMkClientL (I x :* xs) = I (mkClient x) :* gMkClientL xs
type family ClientList (client :: *) (acc :: [*]) :: [*] where
ClientList (a :<|> b) acc = ClientList a (ClientList b acc)
ClientList a acc = a ': acc
class GClientList client (acc :: [*]) where
gClientList :: client -> NP I acc -> NP I (ClientList client acc)
instance (GClientList b acc, GClientList a (ClientList b acc))
=> GClientList (a :<|> b) acc where
gClientList (a :<|> b) acc = gClientList a (gClientList b acc)
instance {-# OVERLAPPABLE #-} (ClientList client acc ~ (client ': acc))
=> GClientList client acc where
gClientList c acc = I c :* acc
-- | Generate client structure from client type, expanding left-nested API (done by default).
genericMkClientL :: (Generic custom, Code custom ~ '[xs], GClientList client '[], GClientLikeL (ClientList client '[]) xs)
=> client -> custom
genericMkClientL = to . SOP . Z . gMkClientL . flip gClientList Nil
-- | Generate client structure from client type, regarding left-nested API clients as separate data structures.
genericMkClientP :: (Generic custom, Code custom ~ '[xs], GClientLikeP client xs)
=> client -> custom
genericMkClientP = to . SOP . Z . gMkClientP