/usr/lib/hugs/packages/mtl/Control/Monad/RWS.hs is in libhugs-mtl-bundled 98.200609.21-5.4+b3.
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-- |
-- Module : Control.Monad.RWS
-- Copyright : (c) Andy Gill 2001,
-- (c) Oregon Graduate Institute of Science and Technology, 2001
-- License : BSD-style (see the file libraries/base/LICENSE)
--
-- Maintainer : libraries@haskell.org
-- Stability : experimental
-- Portability : non-portable (multi-param classes, functional dependencies)
--
-- Declaration of the MonadRWS class.
--
-- Inspired by the paper
-- /Functional Programming with Overloading and
-- Higher-Order Polymorphism/,
-- Mark P Jones (<http://www.cse.ogi.edu/~mpj/>)
-- Advanced School of Functional Programming, 1995.
-----------------------------------------------------------------------------
module Control.Monad.RWS (
RWS(..),
evalRWS,
execRWS,
mapRWS,
withRWS,
RWST(..),
evalRWST,
execRWST,
mapRWST,
withRWST,
module Control.Monad.Reader,
module Control.Monad.Writer,
module Control.Monad.State,
) where
import Prelude
import Control.Monad
import Control.Monad.Fix
import Control.Monad.Trans
import Control.Monad.Reader
import Control.Monad.Writer
import Control.Monad.State
import Data.Monoid
newtype RWS r w s a = RWS { runRWS :: r -> s -> (a, s, w) }
instance Functor (RWS r w s) where
fmap f m = RWS $ \r s -> let
(a, s', w) = runRWS m r s
in (f a, s', w)
instance (Monoid w) => Monad (RWS r w s) where
return a = RWS $ \_ s -> (a, s, mempty)
m >>= k = RWS $ \r s -> let
(a, s', w) = runRWS m r s
(b, s'', w') = runRWS (k a) r s'
in (b, s'', w `mappend` w')
instance (Monoid w) => MonadFix (RWS r w s) where
mfix f = RWS $ \r s -> let (a, s', w) = runRWS (f a) r s in (a, s', w)
instance (Monoid w) => MonadReader r (RWS r w s) where
ask = RWS $ \r s -> (r, s, mempty)
local f m = RWS $ \r s -> runRWS m (f r) s
instance (Monoid w) => MonadWriter w (RWS r w s) where
tell w = RWS $ \_ s -> ((), s, w)
listen m = RWS $ \r s -> let
(a, s', w) = runRWS m r s
in ((a, w), s', w)
pass m = RWS $ \r s -> let
((a, f), s', w) = runRWS m r s
in (a, s', f w)
instance (Monoid w) => MonadState s (RWS r w s) where
get = RWS $ \_ s -> (s, s, mempty)
put s = RWS $ \_ _ -> ((), s, mempty)
evalRWS :: RWS r w s a -> r -> s -> (a, w)
evalRWS m r s = let
(a, _, w) = runRWS m r s
in (a, w)
execRWS :: RWS r w s a -> r -> s -> (s, w)
execRWS m r s = let
(_, s', w) = runRWS m r s
in (s', w)
mapRWS :: ((a, s, w) -> (b, s, w')) -> RWS r w s a -> RWS r w' s b
mapRWS f m = RWS $ \r s -> f (runRWS m r s)
withRWS :: (r' -> s -> (r, s)) -> RWS r w s a -> RWS r' w s a
withRWS f m = RWS $ \r s -> uncurry (runRWS m) (f r s)
newtype RWST r w s m a = RWST { runRWST :: r -> s -> m (a, s, w) }
instance (Monad m) => Functor (RWST r w s m) where
fmap f m = RWST $ \r s -> do
(a, s', w) <- runRWST m r s
return (f a, s', w)
instance (Monoid w, Monad m) => Monad (RWST r w s m) where
return a = RWST $ \_ s -> return (a, s, mempty)
m >>= k = RWST $ \r s -> do
(a, s', w) <- runRWST m r s
(b, s'',w') <- runRWST (k a) r s'
return (b, s'', w `mappend` w')
fail msg = RWST $ \_ _ -> fail msg
instance (Monoid w, MonadPlus m) => MonadPlus (RWST r w s m) where
mzero = RWST $ \_ _ -> mzero
m `mplus` n = RWST $ \r s -> runRWST m r s `mplus` runRWST n r s
instance (Monoid w, MonadFix m) => MonadFix (RWST r w s m) where
mfix f = RWST $ \r s -> mfix $ \ ~(a, _, _) -> runRWST (f a) r s
instance (Monoid w, Monad m) => MonadReader r (RWST r w s m) where
ask = RWST $ \r s -> return (r, s, mempty)
local f m = RWST $ \r s -> runRWST m (f r) s
instance (Monoid w, Monad m) => MonadWriter w (RWST r w s m) where
tell w = RWST $ \_ s -> return ((),s,w)
listen m = RWST $ \r s -> do
(a, s', w) <- runRWST m r s
return ((a, w), s', w)
pass m = RWST $ \r s -> do
((a, f), s', w) <- runRWST m r s
return (a, s', f w)
instance (Monoid w, Monad m) => MonadState s (RWST r w s m) where
get = RWST $ \_ s -> return (s, s, mempty)
put s = RWST $ \_ _ -> return ((), s, mempty)
instance (Monoid w) => MonadTrans (RWST r w s) where
lift m = RWST $ \_ s -> do
a <- m
return (a, s, mempty)
instance (Monoid w, MonadIO m) => MonadIO (RWST r w s m) where
liftIO = lift . liftIO
evalRWST :: (Monad m) => RWST r w s m a -> r -> s -> m (a, w)
evalRWST m r s = do
(a, _, w) <- runRWST m r s
return (a, w)
execRWST :: (Monad m) => RWST r w s m a -> r -> s -> m (s, w)
execRWST m r s = do
(_, s', w) <- runRWST m r s
return (s', w)
mapRWST :: (m (a, s, w) -> n (b, s, w')) -> RWST r w s m a -> RWST r w' s n b
mapRWST f m = RWST $ \r s -> f (runRWST m r s)
withRWST :: (r' -> s -> (r, s)) -> RWST r w s m a -> RWST r' w s m a
withRWST f m = RWST $ \r s -> uncurry (runRWST m) (f r s)
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