Algebra.Monad.Writer

The Writer monad

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

Methods

tell :: w -> m ()

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

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

Instances

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

MonadWriter w m => MonadWriter w (ListT m)

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

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

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

(Monad m, SubSemi acc w, Monoid w) => MonadWriter w (WriterAccT w acc m)

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

(Ring t, Monad m) => MonadWriter (Product t) (ProbT t m)

mute :: (MonadWriter w m, Monoid w) => m a -> m a

intercept :: (MonadWriter w m, Monoid w) => m a -> m (w, a)

intercept' :: (MonadWriter w m, Monoid w) => m a -> m w

eavesdrop :: (MonadWriter w m, Monoid w) => m a -> m w

The Writer transformer

data WriterT w m a

A simple Writer monad

Instances

(Monad m, Monoid w, MonadFuture n m) => MonadFuture n (WriterT w m)

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

(Monoid w, MonadReader r m) => MonadReader r (WriterT w m)

(Monoid w, MonadState r m) => MonadState r (WriterT w m)

Monoid w => MonadTrans (WriterT w)

Monoid w => MonadInternal (WriterT w)

(Unit m, Monoid w) => Unit (WriterT w m)

(Monoid w, MonadCont m) => MonadCont (WriterT w m)

(Monoid w, MonadList m) => MonadList (WriterT w m)

(Monoid w, MonadFix m) => MonadFix (WriterT w m)

Traversable m => Traversable (WriterT w m)

Foldable m => Foldable (WriterT w m)

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

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

Functor m => Functor (WriterT w m)

Ring (m (a, Void, w)) => Ring (WriterT w m a)

Semiring (m (a, Void, w)) => Semiring (WriterT w m a)

Monoid (m (a, Void, w)) => Monoid (WriterT w m a)

Semigroup (m (a, Void, w)) => Semigroup (WriterT w m a)

type Writer w a = WriterT w Id a

writerT :: (Functor m, Functor m') => Iso (WriterT w m a) (WriterT w' m' b) (m (w, a)) (m' (w', b))

writer :: Iso (Writer w a) (Writer w' b) (w, a) (w', b)

pureWriter :: Monoid w => Iso (w, a) (w', b) a b

Keeping track of where we are

class (SubSemi acc w, MonadWriter w m) => MonadWriterAcc w acc m where

Methods

getAcc :: m acc

Instances

MonadWriterAcc w acc m => MonadWriterAcc w acc (StateT s m)

MonadWriterAcc w acc m => MonadWriterAcc w acc (ReaderT r m)

(Monad m, Monoid w, SubSemi acc w) => MonadWriterAcc w acc (WriterAccT w acc m)

Implementation

data WriterAccT w acc m a

The canonical representation of a WriterAcc Monad

Instances

(Monad m, Monoid w, SubSemi acc w) => MonadWriterAcc w acc (WriterAccT w acc m)

(Monad m, Monoid w, MonadFuture n m) => MonadFuture n (WriterAccT w acc m)

(Monad m, SubSemi acc w, Monoid w) => MonadWriter w (WriterAccT w acc m)

(MonadState s m, Monoid w, SubSemi acc w) => MonadState s (WriterAccT w acc m)

Monoid w => MonadTrans (WriterAccT w acc)

(Unit m, Monoid w) => Unit (WriterAccT w acc m)

(Monoid w, MonadFix m) => MonadFix (WriterAccT w acc m)

(Monoid w, Monad m) => Monad (WriterAccT w acc m)

(Monoid w, Monad m) => Applicative (WriterAccT w acc m)

Functor m => Functor (WriterAccT w acc m)

type WriterAcc w acc a = WriterAccT w acc Id a

writerAccT :: (SubSemi acc w, SubSemi acc' w', Monoid acc, Monoid acc', Functor m) => Iso (WriterAccT w acc m a) (WriterAccT w' acc' m' a') (m (a, acc, w)) (m' (a', acc', w'))

writerAcc :: (SubSemi acc w, SubSemi acc' w', Monoid acc, Monoid acc', Functor m) => Iso (WriterAcc w acc a) (WriterAcc w' acc' a') (a, acc, w) (a', acc', w')