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{-# Language TemplateHaskell #-}
module Fig.Web.State where
import Control.Lens.TH (makeLensesFor)
import Control.Lens ((<>=))
import Control.Monad.State (runStateT)
import Fig.Prelude
import qualified Data.IORef as IORef
newtype State = State
{ buffer :: Text
}
makeLensesFor [("buffer", "buffer")] ''State
defaultState :: State
defaultState = State
{ buffer = ""
}
type StateRef = IORef.IORef State
stateRef :: IO StateRef
stateRef = IORef.newIORef defaultState
withState ::
MonadIO m' =>
StateRef ->
(forall m. (MonadIO m, MonadState State m) => m a) ->
m' a
withState ref f = do
s <- liftIO $ IORef.readIORef ref
(res, s') <- liftIO $ runStateT f s
liftIO $ IORef.writeIORef ref s'
pure res
sayHi :: StateRef -> IO ()
sayHi ref = withState ref do
buffer <>= "hi"
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