mtl-1.1.1.0: Monad transformer library

Portabilitynon-portable (multi-param classes, functional dependencies)
Stabilityexperimental
Maintainerlibraries@haskell.org

Control.Monad.Writer.Lazy

Description

Lazy writer monads.

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

newtype Writer w a Source

Constructors

Writer 

Fields

runWriter :: (a, w)
 

Instances

mapWriter :: ((a, w) -> (b, w')) -> Writer w a -> Writer w' bSource

newtype WriterT w m a Source

Constructors

WriterT 

Fields

runWriterT :: m (a, w)
 

Instances

(Monoid w, Monad m) => MonadWriter w (WriterT w m) 
(Monoid w, MonadError e m) => MonadError e (WriterT w m) 
(Monoid w, MonadState s m) => MonadState s (WriterT w m) 
(Monoid w, MonadReader r m) => MonadReader r (WriterT w m) 
Monoid w => MonadTrans (WriterT w) 
(Monoid w, Monad m) => Monad (WriterT w m) 
Monad m => Functor (WriterT w m) 
(Monoid w, MonadFix m) => MonadFix (WriterT w m) 
(Monoid w, MonadPlus m) => MonadPlus (WriterT w m) 
(Monoid w, MonadIO m) => MonadIO (WriterT w m) 
(Monoid w, MonadCont m) => MonadCont (WriterT w m) 

execWriterT :: Monad m => WriterT w m a -> m wSource

mapWriterT :: (m (a, w) -> n (b, w')) -> WriterT w m a -> WriterT w' n bSource