Control.Monad.Writer.Class

Portability	non-portable (type families)
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 (WriterType m), Monad m) => MonadWriter m where

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Associated Types

type WriterType m

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Methods

tell :: WriterType m -> m ()

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listen :: m a -> m (a, WriterType m)

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pass :: m (a, WriterType m -> WriterType m) -> m a

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Instances

MonadWriter m => MonadWriter (MaybeT m)

MonadWriter m => MonadWriter (IdentityT m)

(Monoid w, Monad m) => MonadWriter (WriterT w m)

MonadWriter m => MonadWriter (StateT s m)

MonadWriter m => MonadWriter (ReaderT r m)

(Error e, MonadWriter m) => MonadWriter (ErrorT e m)

(Monoid w, Monad m) => MonadWriter (RWST r w s m)

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

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censor :: MonadWriter m => (WriterType m -> WriterType m) -> m a -> m a

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