Haskell: Parsing and processing stream of json requests - json

Question

Following code tries to execute a stream of Request objects.
{-# LANGUAGE DeriveGeneric, DeriveDataTypeable #-}
--OverloadedStrings,
import Data.Aeson
import Data.Data
import Data.ByteString.Lazy.Internal
import GHC.Generics
import qualified Data.Map as Map
data Request a = Request {
name :: String,
payload :: a
} deriving (Show, Generic)
instance FromJSON a => FromJSON (Request a)
instance ToJSON a => ToJSON (Request a)
class Exe a where
exe :: (Request a) -> String
data Createuser = Createuser {
userName :: String
} deriving (Show, Generic)
instance FromJSON Createuser
instance ToJSON Createuser
instance Exe Createuser where
exe r = "creating user"
parseCreateUser json = parse json :: Request Createuser
data Deleteuser = Deleteuser {
userName2 :: String
} deriving (Show, Generic)
instance FromJSON Deleteuser
instance ToJSON Deleteuser
instance Exe Deleteuser where
exe r = "deleting user"
parseDeleteUser json = parse json :: Request Deleteuser
tojson name payload = encode (Request name payload)
parse bs = let Just p = decode bs in p
sampleDeleteUser = tojson "deleteUser" (Deleteuser "Jigar Gosar")
sampleCreateUser = tojson "createUser" (Createuser "Jigar Gosar")
exeTuple tuple = case tuple of
("createUser", a) -> exe $ parseCreateUser $ a
("deleteUser", a) -> exe $ parseDeleteUser $ a
main = do
-- This list would be read from socket.
let tuples = [("createUser", sampleCreateUser), ("deleteUser", sampleDeleteUser)]
putStr $ unlines [exeTuple tup | tup <- tuples]
print "end"
Is there any way to remove the following duplication?
parseCreateUser json = parse json :: Request Createuser
parseDeleteUser json = parse json :: Request Deleteuser
I will have to write this for every (Request p) I create.
Also I will have to keep modifying following function every time I create new (Request p)
exeTuple tuple = case tuple of
("createUser", a) -> exe $ parseCreateUser $ a
("deleteUser", a) -> exe $ parseDeleteUser $ a
Is this idiomatic haskell code?