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Control.Monad.Writer.Class

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://web.cecs.pdx.edu/~mpj/pubs/springschool.html) 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

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

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