Haskell Hierarchical Libraries (base package)ContentsIndex
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.

Synopsis
class (Monoid w, Monad m) => MonadWriter w m | m -> w where
tell :: w -> m ()
listen :: m a -> m (a, w)
pass :: m (a, w -> w) -> m a
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 = Writer {
runWriter :: (a, w)
}
execWriter :: Writer w a -> w
mapWriter :: ((a, w) -> (b, w')) -> Writer w a -> Writer w' b
newtype WriterT w m a = WriterT {
runWriterT :: (m (a, w))
}
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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