implementation module rwst

from Data.Func import $
import Data.Functor
import Data.Monoid
import Control.Monad
import Control.Applicative


Start = "Test"

:: RWST r w s m a = RWST (r s -> m (a, s, w))

runRWST :: (RWST r w s m a) r s -> m (a, s, w)
runRWST (RWST f) r s = f r s

instance Functor (RWST r w s m) | Monad m & Monoid w where
	fmap f m = liftM f m

instance Applicative (RWST r w s m) | Monad m & Monoid w where
    pure a = RWST \_ s->pure (a, s, mempty)
	(<*>) mf mx = ap mf mx

instance Monad (RWST r w s m) | Monad m & Monoid w where
	bind m k = RWST \r s->runRWST m r s 
		>>= \(a, s`, w)->runRWST (k a) r s`
		>>= \(b, s``,w`)->pure (b, s``, mappend w w`)