2016-11-21 10:56:47 +01:00
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{-# LANGUAGE DataKinds #-}
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{-# LANGUAGE DefaultSignatures #-}
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{-# LANGUAGE FlexibleContexts #-}
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{-# LANGUAGE FlexibleInstances #-}
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{-# LANGUAGE MultiParamTypeClasses #-}
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{-# LANGUAGE TypeFamilies #-}
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{-# LANGUAGE TypeOperators #-}
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module Servant.Client.Generic
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( ClientLike(..)
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, genericMkClient
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) where
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import Generics.SOP (Generic, I(..), NP(..), NS(Z), Rep, SOP(..), to)
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import Servant.API ((:<|>)(..))
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import Servant.Client (ClientM)
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-- | This class allows us to match client structure with client functions
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-- produced with 'client' without explicit pattern-matching.
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--
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-- The client structure needs a 'Generics.SOP.Generic' instance.
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--
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-- Example:
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--
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2016-11-21 13:02:19 +01:00
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-- > type API
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-- > = "foo" :> Capture "x" Int :> Get '[JSON] Int
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-- > :<|> "bar" :> QueryParam "a" Char :> QueryParam "b" String :> Post '[JSON] [Int]
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-- > :<|> Capture "nested" Int :> NestedAPI
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-- >
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-- > type NestedAPI
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-- > = Get '[JSON] String
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-- > :<|> "baz" :> QueryParam "c" Char :> Post '[JSON] ()
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-- >
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-- > data APIClient = APIClient
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-- > { getFoo :: Int -> ClientM Int
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-- > , postBar :: Maybe Char -> Maybe String -> ClientM [Int]
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-- > , mkNestedClient :: Int -> NestedClient
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-- > } deriving GHC.Generic
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-- >
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-- > instance Generic.SOP.Generic APIClient
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-- > instance (Client API ~ client) => ClientLike client APIClient
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-- >
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-- > data NestedClient = NestedClient
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-- > { getString :: ClientM String
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-- > , postBaz :: Maybe Char -> ClientM ()
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-- > } deriving GHC.Generic
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-- >
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-- > instance Generic.SOP.Generic
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-- > instance (Client NestedAPI ~ client) => ClientLike client NestedClient
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-- >
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-- > mkAPIClient :: APIClient
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-- > mkAPIClient = mkClient (client (Proxy :: Proxy API))
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2016-11-21 10:56:47 +01:00
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class ClientLike client custom where
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mkClient :: client -> custom
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default mkClient :: (Generic custom, GClientLikeP client xs, SOP I '[xs] ~ Rep custom)
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=> client -> custom
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mkClient = genericMkClient
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instance ClientLike client custom
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=> ClientLike (a -> client) (a -> custom) where
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mkClient c = mkClient . c
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instance ClientLike (ClientM a) (ClientM a) where
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mkClient = id
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-- | This class is used to match client functions to the
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-- representation of client structure type as sum of products
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-- and basically does all the internal job to build this structure.
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class GClientLikeP client xs where
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gMkClientP :: client -> NP I xs
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instance (GClientLikeP b (y ': xs), ClientLike a x)
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=> GClientLikeP (a :<|> b) (x ': y ': xs) where
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gMkClientP (a :<|> b) = I (mkClient a) :* gMkClientP b
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instance ClientLike a x => GClientLikeP a '[x] where
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gMkClientP a = I (mkClient a) :* Nil
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-- | Generate client structure from client type.
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genericMkClient :: (Generic custom, GClientLikeP client xs, SOP I '[xs] ~ Rep custom)
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=> client -> custom
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genericMkClient = to . SOP . Z . gMkClientP
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