Re: [Haskell-cafe] ANNOUNCE: monad-control-0.3

6 Dec 2011

      On 6 December 2011 04:03, Joey Hess  wrote:
...
I'm trying to convert from 0.2 to 0.3, but in way over my head.
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
newtype Annex a = Annex { runAnnex :: StateT AnnexState IO a }
       deriving (
               Monad,
               MonadIO,
               -- MonadControlIO
               MonadBaseControl IO
       )
You can use the following:

{-# LANGUAGE GeneralizedNewtypeDeriving, TypeFamilies, MultiParamTypeClasses #-}

import Control.Applicative
import Control.Monad
import Control.Monad.Base
import Control.Monad.Trans.Class
import Control.Monad.Trans.Control
import Control.Monad.Trans.State
import Control.Monad.IO.Class

newtype Annex a = Annex { runAnnex :: StateT AnnexState IO a }
       deriving (Applicative, Functor, Monad, MonadIO)

data AnnexState = AnnexState

instance MonadBase IO Annex where
    liftBase = Annex . liftBase

instance MonadBaseControl IO Annex where
    newtype StM Annex a = StAnnex (StM (StateT AnnexState IO) a)
    liftBaseWith f = Annex $ liftBaseWith $ \runInIO ->
                       f $ liftM StAnnex . runInIO . runAnnex

When I have some time I will add some better documentation to monad-control.

Cheers,

Bas

Re: [Haskell-cafe] ANNOUNCE: monad-control-0.3

Bas van Dijk