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Control.Monad.Writer

Portability | non-portable (multi-param classes, functional dependencies)
Stability | experimental
Maintainer | libraries@haskell.org

Description
The MonadWriter 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.
Documentation
class (Monoid w, Monad m) => MonadWriter w m | m -> w where

Methods

tell :: w -> m ()
listen :: m a -> m (a, w)
pass :: m (a, w -> w) -> m a

Instances

(Error e, MonadWriter w m) => MonadWriter w (ErrorT e m)
Monoid w => MonadWriter w (RWS r w s)
(Monoid w, Monad m) => MonadWriter w (RWST r w s m)
MonadWriter w m => MonadWriter w (StateT s m)
Monoid w => MonadWriter w (Writer w)
(Monoid w, Monad m) => MonadWriter w (WriterT w m)
MonadWriter w m => MonadWriter w (ReaderT r m)

listens :: MonadWriter w m => (w -> b) -> m a -> m (a, b)
censor :: MonadWriter w m => (w -> w) -> m a -> m a
newtype Writer w a

Constructors

Writer |

runWriter :: (a, w) |

Instances

Functor (Writer w)
Monoid w => Monad (Writer w)
Monoid w => MonadFix (Writer w)
Monoid w => MonadWriter w (Writer w)

execWriter :: Writer w a -> w
mapWriter :: ((a, w) -> (b, w')) -> Writer w a -> Writer w' b
newtype WriterT w m a

Constructors

WriterT |

runWriterT :: (m (a, w)) |

Instances

(Monoid w, MonadCont m) => MonadCont (WriterT w m)
(Monoid w, MonadError e m) => MonadError e (WriterT w m)
(Monoid w, MonadState s m) => MonadState s (WriterT w m)
Monad m => Functor (WriterT w m)
(Monoid w, Monad m) => Monad (WriterT w m)
(Monoid w, MonadPlus m) => MonadPlus (WriterT w m)
(Monoid w, MonadFix m) => MonadFix (WriterT w m)
(Monoid w, Monad m) => MonadWriter w (WriterT w m)
Monoid w => MonadTrans (WriterT w)
(Monoid w, MonadIO m) => MonadIO (WriterT w m)
(Monoid w, MonadReader r m) => MonadReader r (WriterT w m)

execWriterT :: Monad m => WriterT w m a -> m w
mapWriterT :: (m (a, w) -> n (b, w')) -> WriterT w m a -> WriterT w' n b
module Control.Monad
module Control.Monad.Fix
module Control.Monad.Trans
module Data.Monoid
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