mtl-2.2.2: Monad classes, using functional dependencies

Copyright(c) Andy Gill 2001
(c) Oregon Graduate Institute of Science and Technology 2001
LicenseBSD-style (see the file LICENSE)
Maintainerlibraries@haskell.org
Stabilityexperimental
Portabilitynon-portable (multi-param classes, functional dependencies)
Safe HaskellSafe
LanguageHaskell2010

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.

Synopsis

Documentation

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) Source # 
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) Source #

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

Since: 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) Source # 
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) Source # 
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 (ReaderT r m) Source # 
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 #

MonadWriter w m => MonadWriter w (IdentityT m) Source # 
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) Source #

Since: 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) Source # 
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) Source # 
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) Source # 
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 (RWST r w s m) Source # 
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) Source # 
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.