Modulerio-0.1.22.0Haskell2010

RIO.Writer

Provides reexports of MonadWriter and related helpers.

2 types
1 class
7 values

Packagerio-0.1.22.0
Exports10
LanguageHaskell2010
LicenceMIT
SourceWriter.hs

classclass (Monoid w, Monad m) => MonadWriter w (m :: Type -> Type) | m -> w where

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.

Instances16MonadWriter, …

Monoid w => MonadWriter w (Tuple2 w)Defined in mtl-2.3.1 · Control.Monad.Writer.Class
MonadWriter w m => MonadWriter w (CatchT m)Defined in exceptions-0.10.9 · Control.Monad.Catch.Pure
MonadWriter w m => MonadWriter w (MaybeT m)Defined in mtl-2.3.1 · Control.Monad.Writer.Class
(Monoid w, HasWriteRef w env) => MonadWriter w (RIO env)Defined in rio-0.1.22.0 · RIO.Prelude.RIO
MonadWriter w m => MonadWriter w (ExceptT e m)Defined in mtl-2.3.1 · Control.Monad.Writer.Class
MonadWriter w m => MonadWriter w (IdentityT m)Defined in mtl-2.3.1 · Control.Monad.Writer.Class
MonadWriter w m => MonadWriter w (ReaderT r m)Defined in mtl-2.3.1 · Control.Monad.Writer.Class
MonadWriter w m => MonadWriter w (StateT s m)Defined in mtl-2.3.1 · Control.Monad.Writer.Class
MonadWriter w m => MonadWriter w (StateT s m)Defined in mtl-2.3.1 · Control.Monad.Writer.Class
(Monoid w, Monad m) => MonadWriter w (WriterT w m)Defined in mtl-2.3.1 · Control.Monad.Writer.Class
(Monoid w, Monad m) => MonadWriter w (WriterT w m)Defined in mtl-2.3.1 · Control.Monad.Writer.Class
(Monoid w, Monad m) => MonadWriter w (WriterT w m)Defined in mtl-2.3.1 · Control.Monad.Writer.Class
(Monoid w', MonadWriter w m) => MonadWriter w (AccumT w' m)Defined in mtl-2.3.1 · Control.Monad.Writer.Class
There are two valid instances for AccumT. It could either:
1. Lift the operations to the inner MonadWriter
2. Handle the operations itself, à la a WriterT.
This instance chooses (1), reflecting that the intent of AccumT as a type is different than that of WriterT.
(Monoid w, Monad m) => MonadWriter w (RWST r w s m)Defined in mtl-2.3.1 · Control.Monad.Writer.Class
(Monoid w, Monad m) => MonadWriter w (RWST r w s m)Defined in mtl-2.3.1 · Control.Monad.Writer.Class
(Monoid w, Monad m) => MonadWriter w (RWST r w s m)Defined in mtl-2.3.1 · Control.Monad.Writer.Class

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

listens f m is an action that executes the action m and adds the result of applying f to the output to the value of the computation.

listens f m = liftM (id *** f) (listen m)

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

censor f m is an action that executes the action m and applies the function f to its output, leaving the return value unchanged.

censor f m = pass (liftM (\x -> (x,f)) m)

typetype Writer w = WriterT w Identity

A writer monad parameterized by the type w of output to accumulate.

The return function produces the output mempty, while m >>= k combines the outputs of the subcomputations using mappend (also known as <>):

image: images/bind-WriterT.svg

valuerunWriter :: Writer w a -> (a, w)

Unwrap a writer computation as a (result, output) pair. (The inverse of writer.)

valueexecWriter :: Writer w a -> w

Extract the output from a writer computation.

```
execWriter m = snd (runWriter m)
```

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

Map both the return value and output of a computation using the given function.

runWriter (mapWriter f m) = f (runWriter m)

newtypenewtype WriterT w (m :: Type -> Type) a

A writer monad parameterized by:

w - the output to accumulate.
m - The inner monad.

The return function produces the output mempty, while m >>= k combines the outputs of the subcomputations using mappend (also known as <>):

image: images/bind-WriterT.svg

Constructors

WriterT
- runWriterT :: m (a, w)

Instances37MonadAccum, MonadError, MonadReader, MonadState, MonadWriter, MonadSelect, …

(MonadAccum w' m, Monoid w) => MonadAccum w' (WriterT w m)Defined in mtl-2.3.1 · Control.Monad.Accum
(Monoid w, MonadError e m) => MonadError e (WriterT w m)Defined in mtl-2.3.1 · Control.Monad.Error.Class
(Monoid w, MonadReader r m) => MonadReader r (WriterT w m)Defined in mtl-2.3.1 · Control.Monad.Reader.Class
(Monoid w, MonadState s m) => MonadState s (WriterT w m)Defined in mtl-2.3.1 · Control.Monad.State.Class
(Monoid w, Monad m) => MonadWriter w (WriterT w m)Defined in mtl-2.3.1 · Control.Monad.Writer.Class
(MonadSelect w' m, Monoid w) => MonadSelect w' (WriterT w m)Defined in mtl-2.3.1 · Control.Monad.Select
'Readerizes' the writer: the 'ranking' function can see the value that's been accumulated (of type w), but can't add anything to the log. Effectively, can be thought of as 'extending' the 'ranking' by all values of w, but which w gets given to any rank calls is predetermined by the 'outer writer' (and cannot change).
Monoid w => MonadTrans (WriterT w)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
(Monoid w, Monad m) => Monad (WriterT w m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
Functor m => Functor (WriterT w m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
(Monoid w, MonadFix m) => MonadFix (WriterT w m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
(Monoid w, MonadFail m) => MonadFail (WriterT w m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
(Monoid w, Applicative m) => Applicative (WriterT w m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
Foldable f => Foldable (WriterT w f)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
Traversable f => Traversable (WriterT w f)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
(Monoid w, Alternative m) => Alternative (WriterT w m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
(Monoid w, MonadPlus m) => MonadPlus (WriterT w m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
(Monoid w, MonadIO m) => MonadIO (WriterT w m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
(Monoid w, MonadZip m) => MonadZip (WriterT w m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
(Eq w, Eq1 m) => Eq1 (WriterT w m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
(Ord w, Ord1 m) => Ord1 (WriterT w m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
(Read w, Read1 m) => Read1 (WriterT w m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
(Show w, Show1 m) => Show1 (WriterT w m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
Contravariant m => Contravariant (WriterT w m)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
(Monoid w, MonadCont m) => MonadCont (WriterT w m)Defined in mtl-2.3.1 · Control.Monad.Cont.Class
(MonadCatch m, Monoid w) => MonadCatch (WriterT w m)Defined in exceptions-0.10.9 · Control.Monad.Catch
(MonadMask m, Monoid w) => MonadMask (WriterT w m)Defined in exceptions-0.10.9 · Control.Monad.Catch
(MonadThrow m, Monoid w) => MonadThrow (WriterT w m)Defined in exceptions-0.10.9 · Control.Monad.Catch
(Monoid w, PrimMonad m) => PrimMonad (WriterT w m)Defined in primitive-0.9.1.0 · Control.Monad.Primitive
(Monoid w, Zoom m n s t) => Zoom (WriterT w m) (WriterT w n) s tDefined in microlens-mtl-0.2.1.0 · Lens.Micro.Mtl.Internal
(Eq w, Eq1 m, Eq a) => Eq (WriterT w m a)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
(Ord w, Ord1 m, Ord a) => Ord (WriterT w m a)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
(Read w, Read1 m, Read a) => Read (WriterT w m a)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
(Show w, Show1 m, Show a) => Show (WriterT w m a)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
Generic (WriterT w m a)Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
type Rep (WriterT w m a) = D1 ('MetaData "WriterT" "Control.Monad.Trans.Writer.Lazy" "transformers-0.6.1.1-a11a" 'True) (C1 ('MetaCons "WriterT" 'PrefixI 'True) (S1 ('MetaSel ('Just "runWriterT") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 (m (a, w)))))Defined in transformers-0.6.1.1 · Control.Monad.Trans.Writer.Lazy
type PrimState (WriterT w m) = PrimState mDefined in primitive-0.9.1.0 · Control.Monad.Primitive
type Zoomed (WriterT w m) = FocusingPlus w (Zoomed m)Defined in microlens-mtl-0.2.1.0 · Lens.Micro.Mtl.Internal

valueexecWriterT :: Monad m => WriterT w m a -> m w

Extract the output from a writer computation.

execWriterT m = liftM snd (runWriterT m)

valuemapWriterT :: (m (a, w) -> n (b, w')) -> WriterT w m a -> WriterT w' n b

Map both the return value and output of a computation using the given function.

runWriterT (mapWriterT f m) = f (runWriterT m)