DeepControl.Monad.Writer

Documentation

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

Minimal complete definition

(writer | tell), listen, pass

Methods

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

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

tell :: w -> m ()

tell w is an action that produces the output w.

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

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

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)

MonadWriter w m => MonadWriter w (IdentityT m)

Monoid w => MonadWriter w (Writer w)

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

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

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

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

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

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

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

Monoid w => MonadWriter w (RWS r w s)

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

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

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

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

newtype Writer w a

Constructors

Writer

Fields

runWriter :: (a, w)

Instances

Monoid w => MonadWriter w (Writer w)

Monoid w => Monad (Writer w)

Functor (Writer w)

Monoid w => Applicative (Writer w)

Monoid w => Monad5 (Writer w)

Monoid w => Monad4 (Writer w)

Monoid w => Monad3 (Writer w)

Monoid w => Monad2 (Writer w)

execWriter :: Writer w a -> w