Control.Monad.Writer.Lazy

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

module Control.Monad.Writer.Class

newtype Writer w a

Constructors

Writer

Fields

runWriter :: (a, w)

Instances

(Monoid w, MonadTrans t, Monad (t (Writer w)), Monad (t (State w))) => MonadWriter w (t (Writer w))

Monoid w => MonadWriter w (Writer w)

Monoid w => Monad (Writer w)

Functor (Writer w)

Monoid w => MonadFix (Writer w)

execWriter :: Writer w a -> w

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

newtype WriterT w m a

Constructors

WriterT

Fields

runWriterT :: m (a, w)

Instances

(Monoid w, Monad m, MonadTrans t, Monad (t (WriterT w m)), Monad (t (StateT w m))) => MonadWriter w (t (WriterT w m))

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

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