mtl-1.1.1.0: Monad transformer library

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

Control.Monad.Writer.Class

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) |
MonadWriter w m => MonadWriter w (ReaderT r m) |
(Error e, MonadWriter w m) => MonadWriter w (ErrorT e 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