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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 Control.Monad.IO.Unlift (MonadUnliftIO(..))
import Data.Text.Lazy (pack)
import Web.Scotty.Trans (ScottyT, defaultOptions, 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, MonadUnliftIO)
application :: ScottyT ConfigM ()
application = do
get "/" $ do
e <- lift $ asks environment
text $ pack $ show e
main :: IO ()
main = scottyOptsT defaultOptions runIO application where
runIO :: ConfigM a -> IO a
runIO m = runReaderT (runConfigM m) config
config :: Config
config = Config
{ environment = "Development"
}
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