git.iko.soy/servant
on master help sign in
genericServeT and docs on using a custom monad with generics
c1e15efKostiantyn Rybnikov
doc/cookbook/generic/Generic.lhs+42−1
compare with master
unifiedsplit
@@ -5,7 +5,7 @@
5{-# LANGUAGE DeriveGeneric #-}
5{-# LANGUAGE DeriveGeneric #-}
6{-# LANGUAGE RankNTypes #-}
6{-# LANGUAGE RankNTypes #-}
7{-# LANGUAGE TypeOperators #-}
7{-# LANGUAGE TypeOperators #-}
8−module Main (main, api, getLink, routesLinks, cliGet) where
8+module Main (main, api, getLink, routesLinks, cliGet, mainMyMonad) where
9
9
10import Control.Exception (throwIO)
10import Control.Exception (throwIO)
11import Data.Proxy (Proxy (..))
11import Data.Proxy (Proxy (..))
@@ -104,3 +104,44 @@ main = do
104 run 8000 app
104 run 8000 app
105 _ -> putStrLn "To run, pass 'run' argument: cabal new-run cookbook-generic run"
105 _ -> putStrLn "To run, pass 'run' argument: cabal new-run cookbook-generic run"
106```
106```
107+
108+## Using generics together with a custom monad
109+
110+If your app uses a custom monad, here's how you can combine it with
111+generics.
112+
113+```haskell
114+data AppCustomState =
115+ AppCustomState
116+
117+type AppM = ReaderT AppCustomState Handler
118+
119+apiMyMonad :: Proxy (ToServantApi Routes)
120+apiMyMonad = genericApi (Proxy :: Proxy Routes)
121+
122+getRouteMyMonad :: Int -> AppM String
123+getRouteMyMonad = return . show
124+
125+putRouteMyMonad :: Int -> AppM Bool
126+putRouteMyMonad = return . odd
127+
128+recordMyMonad :: Routes (AsServerT AppM)
129+recordMyMonad = Routes {_get = getRouteMyMonad, _put = putRouteMyMonad}
130+
131+-- natural transformation
132+nt :: AppCustomState -> AppM a -> Handler a
133+nt s x = runReaderT x s
134+
135+appMyMonad :: AppCustomState -> Application
136+appMyMonad state = genericServeT (nt state) recordMyMonad
137+
138+mainMyMonad :: IO ()
139+mainMyMonad = do
140+ args <- getArgs
141+ case args of
142+ ("run":_) -> do
143+ putStrLn "Starting cookbook-generic at http://localhost:8000"
144+ run 8000 (appMyMonad AppCustomState)
145+ _ ->
146+ putStrLn "To run, pass 'run' argument: cabal new-run cookbook-generic run"
147+```
servant-server/src/Servant/Server/Generic.hs+42
@@ -2,6 +2,7 @@
2{-# LANGUAGE DataKinds #-}
2{-# LANGUAGE DataKinds #-}
3{-# LANGUAGE FlexibleContexts #-}
3{-# LANGUAGE FlexibleContexts #-}
4{-# LANGUAGE KindSignatures #-}
4{-# LANGUAGE KindSignatures #-}
5+{-# LANGUAGE RankNTypes #-}
5{-# LANGUAGE ScopedTypeVariables #-}
6{-# LANGUAGE ScopedTypeVariables #-}
6{-# LANGUAGE TypeFamilies #-}
7{-# LANGUAGE TypeFamilies #-}
7{-# LANGUAGE TypeOperators #-}
8{-# LANGUAGE TypeOperators #-}
@@ -11,6 +12,8 @@ module Servant.Server.Generic (
11 AsServerT,
12 AsServerT,
12 AsServer,
13 AsServer,
13 genericServe,
14 genericServe,
15+ genericServeT,
16+ genericServeT',
14 genericServer,
17 genericServer,
15 genericServerT,
18 genericServerT,
16 ) where
19 ) where
@@ -38,6 +41,45 @@ genericServe
38 => routes AsServer -> Application
41 => routes AsServer -> Application
39genericServe = serve (Proxy :: Proxy (ToServantApi routes)) . genericServer
42genericServe = serve (Proxy :: Proxy (ToServantApi routes)) . genericServer
40
43
44+-- | Transform a record of routes with custom monad into a WAI 'Application',
45+-- by providing a transformation to bring each handler back in the 'Handler'
46+-- monad.
47+genericServeT
48+ :: forall (routes :: * -> *) (m :: * -> *).
49+ ( GenericServant routes (AsServerT m)
50+ , GenericServant routes AsApi
51+ , HasServer (ToServantApi routes) '[]
52+ , ServerT (ToServantApi routes) m ~ ToServant routes (AsServerT m)
53+ )
54+ => (forall a. m a -> Handler a) -- ^ 'hoistServer' argument to come back to 'Handler'
55+ -> routes (AsServerT m) -- ^ your record full of request handlers
56+ -> Application
57+genericServeT f server = serve p $ hoistServer p f (genericServerT server)
58+ where
59+ p = genericApi (Proxy :: Proxy routes)
60+
61+-- | Transform a record of routes with custom monad into a WAI 'Application',
62+-- while using the given 'Context' to serve the application (contexts are typically
63+-- used by auth-related combinators in servant, e.g to hold auth checks) and the given
64+-- transformation to map all the handlers back to the 'Handler' monad.
65+genericServeT'
66+ :: forall (routes :: * -> *) (m :: * -> *) (ctx :: [*]).
67+ ( GenericServant routes (AsServerT m)
68+ , GenericServant routes AsApi
69+ , HasServer (ToServantApi routes) ctx
70+ , ServerT (ToServantApi routes) m ~ ToServant routes (AsServerT m)
71+ )
72+ => (forall a. m a -> Handler a) -- ^ 'hoistServer' argument to come back to 'Handler'
73+ -> routes (AsServerT m) -- ^ your record full of request handlers
74+ -> Context ctx -- ^ the 'Context' to serve the application with
75+ -> Application
76+genericServeT' f server ctx =
77+ serveWithContext p ctx $
78+ hoistServerWithContext p pctx f (genericServerT server)
79+ where
80+ p = genericApi (Proxy :: Proxy routes)
81+ pctx = Proxy :: Proxy ctx
82+
41-- | Transform record of endpoints into a 'Server'.
83-- | Transform record of endpoints into a 'Server'.
42genericServer
84genericServer
43 :: GenericServant routes AsServer
85 :: GenericServant routes AsServer