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/Haskell 8

Control.Monad.Writer.Class

Copyright (c) Andy Gill 2001
(c) Oregon Graduate Institute of Science and Technology 2001
License BSD-style (see the file LICENSE)
Maintainer [email protected]
Stability experimental
Portability non-portable (multi-param classes, functional dependencies)
Safe Haskell Safe
Language Haskell2010

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.

class (Monoid w, Monad m) => MonadWriter w m | m -> w where Source

Minimal complete definition

(writer | tell), listen, pass

Methods

writer :: (a, w) -> m a Source

writer (a,w) embeds a simple writer action.

tell :: w -> m () Source

tell w is an action that produces the output w.

listen :: m a -> m (a, w) Source

listen m is an action that executes the action m and adds its output to the value of the computation.

pass :: m (a, w -> w) -> m a Source

pass m is an action that executes the action m, which returns a value and a function, and returns the value, applying the function to the output.

Instances
MonadWriter w m => MonadWriter w (MaybeT m)
Instance details

Defined in Control.Monad.Writer.Class

Methods

writer :: (a, w) -> MaybeT m a Source

tell :: w -> MaybeT m () Source

listen :: MaybeT m a -> MaybeT m (a, w) Source

pass :: MaybeT m (a, w -> w) -> MaybeT m a Source

Monoid w => MonadWriter w ((,) w)

NOTE: This instance is only defined for base >= 4.9.0.

Since: mtl-2.2.2

Instance details

Defined in Control.Monad.Writer.Class

Methods

writer :: (a, w) -> (w, a) Source

tell :: w -> (w, ()) Source

listen :: (w, a) -> (w, (a, w)) Source

pass :: (w, (a, w -> w)) -> (w, a) Source

MonadWriter w m => MonadWriter w (StateT s m)
Instance details

Defined in Control.Monad.Writer.Class

Methods

writer :: (a, w) -> StateT s m a Source

tell :: w -> StateT s m () Source

listen :: StateT s m a -> StateT s m (a, w) Source

pass :: StateT s m (a, w -> w) -> StateT s m a Source

MonadWriter w m => MonadWriter w (StateT s m)
Instance details

Defined in Control.Monad.Writer.Class

Methods

writer :: (a, w) -> StateT s m a Source

tell :: w -> StateT s m () Source

listen :: StateT s m a -> StateT s m (a, w) Source

pass :: StateT s m (a, w -> w) -> StateT s m a Source

MonadWriter w m => MonadWriter w (IdentityT m)
Instance details

Defined in Control.Monad.Writer.Class

Methods

writer :: (a, w) -> IdentityT m a Source

tell :: w -> IdentityT m () Source

listen :: IdentityT m a -> IdentityT m (a, w) Source

pass :: IdentityT m (a, w -> w) -> IdentityT m a Source

MonadWriter w m => MonadWriter w (ExceptT e m)

Since: mtl-2.2

Instance details

Defined in Control.Monad.Writer.Class

Methods

writer :: (a, w) -> ExceptT e m a Source

tell :: w -> ExceptT e m () Source

listen :: ExceptT e m a -> ExceptT e m (a, w) Source

pass :: ExceptT e m (a, w -> w) -> ExceptT e m a Source

(Error e, MonadWriter w m) => MonadWriter w (ErrorT e m)
Instance details

Defined in Control.Monad.Writer.Class

Methods

writer :: (a, w) -> ErrorT e m a Source

tell :: w -> ErrorT e m () Source

listen :: ErrorT e m a -> ErrorT e m (a, w) Source

pass :: ErrorT e m (a, w -> w) -> ErrorT e m a Source

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

Defined in Control.Monad.Writer.Class

Methods

writer :: (a, w) -> WriterT w m a Source

tell :: w -> WriterT w m () Source

listen :: WriterT w m a -> WriterT w m (a, w) Source

pass :: WriterT w m (a, w -> w) -> WriterT w m a Source

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

Defined in Control.Monad.Writer.Class

Methods

writer :: (a, w) -> WriterT w m a Source

tell :: w -> WriterT w m () Source

listen :: WriterT w m a -> WriterT w m (a, w) Source

pass :: WriterT w m (a, w -> w) -> WriterT w m a Source

MonadWriter w m => MonadWriter w (ReaderT r m)
Instance details

Defined in Control.Monad.Writer.Class

Methods

writer :: (a, w) -> ReaderT r m a Source

tell :: w -> ReaderT r m () Source

listen :: ReaderT r m a -> ReaderT r m (a, w) Source

pass :: ReaderT r m (a, w -> w) -> ReaderT r m a Source

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

Defined in Control.Monad.Writer.Class

Methods

writer :: (a, w) -> RWST r w s m a Source

tell :: w -> RWST r w s m () Source

listen :: RWST r w s m a -> RWST r w s m (a, w) Source

pass :: RWST r w s m (a, w -> w) -> RWST r w s m a Source

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

Defined in Control.Monad.Writer.Class

Methods

writer :: (a, w) -> RWST r w s m a Source

tell :: w -> RWST r w s m () Source

listen :: RWST r w s m a -> RWST r w s m (a, w) Source

pass :: RWST r w s m (a, w -> w) -> RWST r w s m a Source

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

listens f m is an action that executes the action m and adds the result of applying f to the output to the value of the computation.

censor :: MonadWriter w m => (w -> w) -> m a -> m a Source

censor f m is an action that executes the action m and applies the function f to its output, leaving the return value unchanged.

© The University of Glasgow and others
Licensed under a BSD-style license (see top of the page).
https://downloads.haskell.org/~ghc/8.6.1/docs/html/libraries/mtl-2.2.2/Control-Monad-Writer-Class.html