Control.Monad.Ether.Writer

See Control.Monad.Writer.

MonadWriter class

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

See MonadWriter.

Minimal complete definition

(writer | tell), listen, pass

Methods

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

Embed a simple writer action.

tell :: proxy tag -> w -> m ()

Append a value to the accumulator within the monad.

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

Execute an action and add its accumulator to the value of the computation.

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

Execute an action which returns a value and a function, and return the value, applying the function to the accumulator.

Instances

(LiftListen t, LiftPass t, Monad (t m), MonadWriter tag w m, Monoid w) => MonadWriter tag w (t m)

MonadWriter tag w m => MonadWriter tag w (WrappedEther tag' m)

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

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

Execute an action and add the result of applying the given function to its accumulator to the value of the computation.

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

Execute an action and apply a function to its accumulator.

The Writer monad

type Writer tag w = WriterT tag w Identity

The parametrizable writer monad.

Computations can accumulate a monoid value.

The return function produces the output mempty, while >>= combines the outputs of the subcomputations using mappend.

runWriter :: proxy tag -> Writer tag w a -> (a, w)

Runs a Writer and returns both the normal value and the final accumulator.

execWriter :: proxy tag -> Writer tag w a -> w

Runs a Writer and returns the final accumulator, discarding the normal value.

The WriterT monad transformer

data WriterT tag w m a

The writer monad transformer.

The return function produces the output mempty, while >>= combines the outputs of the subcomputations using mappend.

Instances

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

(Monoid w, MonadState tag s m) => MonadState tag s (WriterT tag' w m)

(Monoid w, MonadBase b m) => MonadBase b (WriterT tag w m)

(Monoid w, MonadBaseControl b m) => MonadBaseControl b (WriterT tag w m)

(Monoid w, MonadError e m) => MonadError e (WriterT tag w m)

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

(Monoid w, MonadState s m) => MonadState s (WriterT tag w m)

(Monoid w, MonadWriter w' m) => MonadWriter w' (WriterT tag w m)

MFunctor (WriterT tag w)

Monoid w => MMonad (WriterT tag w)

Monoid w => MonadTrans (WriterT tag w)

Monoid w => MonadTransControl (WriterT tag w)

Monoid w => LiftLocal (WriterT tag w)

Monoid w => LiftCallCC (WriterT tag w)

Monoid w' => LiftPass (WriterT tag w')

Monoid w => LiftListen (WriterT tag w)

Monoid w => LiftCatch (WriterT tag w)

(Alternative m, Monoid w) => Alternative (WriterT tag w m)

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

Functor m => Functor (WriterT tag w m)

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

(MonadPlus m, Monoid w) => MonadPlus (WriterT tag w m)

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

(Monoid w, MonadIO m) => MonadIO (WriterT tag w m)

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

Taggable (WriterT tag w m)

Tagged (WriterT tag w m) tag

Generic (WriterT tag w m a)

Newtype (WriterT tag w m a)

type StT (WriterT tag w) a = StT (WriterT w) a

type StT (WriterT tag w) a = StT (WriterT tag w) a

type Untagged (WriterT tag w m) = WriterT w m

type Tag (WriterT tag w m) = Just * tag

type Inner (WriterT tag w m) = Just (* -> *) m

type StM (WriterT tag w m) a = ComposeSt (WriterT tag w) m a

type Rep (WriterT tag w m a)

type O (WriterT tag w m a) = GO (Rep (WriterT tag w m a))

writerT :: proxy tag -> m (a, w) -> WriterT tag w m a

Constructor for computations in the writer monad transformer.

runWriterT :: proxy tag -> WriterT tag w m a -> m (a, w)

Runs a WriterT and returns both the normal value and the final accumulator.

execWriterT :: Monad m => proxy tag -> WriterT tag w m a -> m w

Runs a WriterT and returns the final accumulator, discarding the normal value.