Control.Monad.Writer.Class

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 w, Monad m) => MonadWriter w m | m -> w where

Methods

tell :: w -> m ()

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

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

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

Monoid w => MonadWriter w (Writer w)

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

(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 m) => MonadWriter w (WriterT w m)

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

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

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