Hi all,
The STM monad currently has no MonadFix instance, but wonderful things are possible when it has one.
I propose adding the 'MonadFix STM' instance provided by Antoine Latter on the Haskell-Cafe[1] list to the STM package:
> {-# LANGUAGE MagicHash, UnboxedTuples, DoRec #-}
>
> import GHC.Exts
> import GHC.Conc
> import Control.Monad.Fix
>
> data STMret a = STMret (State# RealWorld) a
>
> liftSTM :: STM a -> State# RealWorld -> STMret a
> liftSTM (STM m) = \s -> case m s of (# s', r #) -> STMret s' r
>
> instance MonadFix STM where
> mfix k = STM $ \s ->
> let ans = liftSTM (k r) s
> STMret _ r = ans
> in case ans of STMret s' x -> (# s', x #)
Discussion Period: 1 week
-Sebastiaan Visser
[1] http://www.haskell.org/pipermail/haskell-cafe/2011-February/089226.html
_______________________________________________
Libraries mailing list
Libraries@haskell.org
http://www.haskell.org/mailman/listinfo/libraries