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{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE OverloadedStrings #-}
{-
An example of embedding a custom monad into Scotty's transformer
stack, using ReaderT to provide access to a global state.
-}
module Main where
import Control.Monad.Reader (MonadIO, MonadReader, ReaderT, asks, lift, runReaderT)
import Data.Default.Class (def)
import Data.Text.Lazy (Text, pack)
import Prelude ()
import Prelude.Compat
import Web.Scotty.Trans (ScottyT, get, scottyOptsT, text)
data Config = Config
{ environment :: String
} deriving (Eq, Read, Show)
newtype ConfigM a = ConfigM
{ runConfigM :: ReaderT Config IO a
} deriving (Applicative, Functor, Monad, MonadIO, MonadReader Config)
application :: ScottyT Text ConfigM ()
application = do
get "/" $ do
e <- lift $ asks environment
text $ pack $ show e
main :: IO ()
main = scottyOptsT def runIO application where
runIO :: ConfigM a -> IO a
runIO m = runReaderT (runConfigM m) config
config :: Config
config = Config
{ environment = "Development"
}
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