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

[Bas van Dijk]

On 6 December 2011 04:03, Joey Hess <joey at kitenet.net> 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