git.iko.soy/servant
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servant/src/Servant/API/GetParam.hs
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1{-# LANGUAGE PolyKinds #-}
2{-# LANGUAGE TypeFamilies #-}
3{-# LANGUAGE TypeOperators #-}
4{-# LANGUAGE FlexibleInstances #-}
5{-# LANGUAGE ScopedTypeVariables #-}
6module Servant.API.GetParam where
8import Data.Proxy
9import Data.String.Conversions
10import Data.Text
11import GHC.TypeLits
12import Network.HTTP.Types
13import Network.Wai
14import Servant.API.Sub
15import Servant.Client
16import Servant.Server
17import Servant.Text
19-- * GET params support (i.e query string arguments)
20data GetParam sym a
22instance (KnownSymbol sym, FromText a, HasServer sublayout)
23 => HasServer (GetParam sym a :> sublayout) where
25 type Server (GetParam sym a :> sublayout) =
26 Maybe a -> Server sublayout
28 route Proxy subserver request = do
29 let querytext = parseQueryText $ rawQueryString request
30 param =
31 case lookup paramName querytext of
32 Nothing -> Nothing -- param absent from the query string
33 Just Nothing -> Nothing -- param present with no value -> Nothing
34 Just (Just v) -> fromText v -- if present, we try to convert to
35 -- the right type
37 route (Proxy :: Proxy sublayout) (subserver param) request
39 where paramName = cs $ symbolVal (Proxy :: Proxy sym)
41instance (KnownSymbol sym, ToText a, HasClient sublayout)
42 => HasClient (GetParam sym a :> sublayout) where
44 type Client (GetParam sym a :> sublayout) =
45 Maybe a -> Client sublayout
47 -- if mparam = Nothing, we don't add it to the query string
48 clientWithRoute Proxy req mparam =
49 clientWithRoute (Proxy :: Proxy sublayout) $
50 appendToQueryString pname mparamText req
52 where pname = pack pname'
53 pname' = symbolVal (Proxy :: Proxy sym)
54 mparamText = fmap toText mparam