Re: [Haskell-cafe] Fighting the monad stack, MonadIO

10 Apr 2008


      On Thu, Apr 10, 2008 at 12:44 PM, Antoine Latter  wrote:
...
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
import Control.Monad.Trans
 import Control.Monad.State
 import Control.Monad.Error
type BrowserAction = IO  -- or something else which is in MondaIO
 data RBState = RBState
newtype RBAction a = RBAction
   { exec :: ErrorT String (StateT RBState BrowserAction) a }
   deriving (Functor, Monad, MonadState RBState, MonadIO)
D'oh!  Deriving MonadIO for the newtype should work, so long as
BrowserAction is in the MonadIO class.

-Antoine