Safe Haskell	Safe
Language	Haskell2010

RIO.Writer

Description

Provides reexports of MonadWriter and related helpers.

Since: 0.1.4.0

Synopsis

class (Monoid w, Monad m) => MonadWriter w (m :: Type -> Type) | m -> w where
- writer :: (a, w) -> m a
- tell :: w -> m ()
- listen :: m a -> m (a, w)
- pass :: m (a, w -> w) -> m a
listens :: MonadWriter w m => (w -> b) -> m a -> m (a, b)
censor :: MonadWriter w m => (w -> w) -> m a -> m a
type Writer w = WriterT w Identity
runWriter :: Writer w a -> (a, w)
execWriter :: Writer w a -> w
mapWriter :: ((a, w) -> (b, w')) -> Writer w a -> Writer w' b
newtype WriterT w (m :: Type -> Type) a = WriterT {
- runWriterT :: m (a, w)
}
execWriterT :: Monad m => WriterT w m a -> m w
mapWriterT :: (m (a, w) -> n (b, w')) -> WriterT w m a -> WriterT w' n b

Documentation

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

(Monoid w, HasWriteRef w env) => MonadWriter w (RIO env) Source #
Instance details Defined in RIO.Prelude.RIO Methods writer :: (a, w) -> RIO env a # tell :: w -> RIO env () # listen :: RIO env a -> RIO env (a, w) # pass :: RIO env (a, w -> w) -> RIO env a #
MonadWriter w m => MonadWriter w (MaybeT m)
Instance details Defined in Control.Monad.Writer.Class Methods writer :: (a, w) -> MaybeT m a # tell :: w -> MaybeT m () # listen :: MaybeT m a -> MaybeT m (a, w) # pass :: MaybeT m (a, w -> w) -> MaybeT m a #
Monoid w => MonadWriter w ((,) w)	NOTE: This instance is only defined for `base >= 4.9.0`. Since: mtl-2.2.2
Instance details Defined in Control.Monad.Writer.Class Methods writer :: (a, w) -> (w, a) # tell :: w -> (w, ()) # listen :: (w, a) -> (w, (a, w)) # pass :: (w, (a, w -> w)) -> (w, a) #
(Monoid w, Monad m) => MonadWriter w (WriterT w m)
Instance details Defined in Control.Monad.Writer.Class Methods writer :: (a, w) -> WriterT w m a # tell :: w -> WriterT w m () # listen :: WriterT w m a -> WriterT w m (a, w) # pass :: WriterT w m (a, w -> w) -> WriterT w m a #
(Monoid w, Monad m) => MonadWriter w (WriterT w m)
Instance details Defined in Control.Monad.Writer.Class Methods writer :: (a, w) -> WriterT w m a # tell :: w -> WriterT w m () # listen :: WriterT w m a -> WriterT w m (a, w) # pass :: WriterT w m (a, w -> w) -> WriterT w m a #
MonadWriter w m => MonadWriter w (StateT s m)
Instance details Defined in Control.Monad.Writer.Class Methods writer :: (a, w) -> StateT s m a # tell :: w -> StateT s m () # listen :: StateT s m a -> StateT s m (a, w) # pass :: StateT s m (a, w -> w) -> StateT s m a #
MonadWriter w m => MonadWriter w (StateT s m)
Instance details Defined in Control.Monad.Writer.Class Methods writer :: (a, w) -> StateT s m a # tell :: w -> StateT s m () # listen :: StateT s m a -> StateT s m (a, w) # pass :: StateT s m (a, w -> w) -> StateT s m a #
MonadWriter w m => MonadWriter w (IdentityT m)
Instance details Defined in Control.Monad.Writer.Class Methods writer :: (a, w) -> IdentityT m a # tell :: w -> IdentityT m () # listen :: IdentityT m a -> IdentityT m (a, w) # pass :: IdentityT m (a, w -> w) -> IdentityT m a #
MonadWriter w m => MonadWriter w (ExceptT e m)	Since: mtl-2.2
Instance details Defined in Control.Monad.Writer.Class Methods writer :: (a, w) -> ExceptT e m a # tell :: w -> ExceptT e m () # listen :: ExceptT e m a -> ExceptT e m (a, w) # pass :: ExceptT e m (a, w -> w) -> ExceptT e m a #
(Error e, MonadWriter w m) => MonadWriter w (ErrorT e m)
Instance details Defined in Control.Monad.Writer.Class Methods writer :: (a, w) -> ErrorT e m a # tell :: w -> ErrorT e m () # listen :: ErrorT e m a -> ErrorT e m (a, w) # pass :: ErrorT e m (a, w -> w) -> ErrorT e m a #
MonadWriter w m => MonadWriter w (ReaderT r m)
Instance details Defined in Control.Monad.Writer.Class Methods writer :: (a, w) -> ReaderT r m a # tell :: w -> ReaderT r m () # listen :: ReaderT r m a -> ReaderT r m (a, w) # pass :: ReaderT r m (a, w -> w) -> ReaderT r m a #
(Monoid w, Monad m) => MonadWriter w (RWST r w s m)
Instance details Defined in Control.Monad.Writer.Class Methods writer :: (a, w) -> RWST r w s m a # tell :: w -> RWST r w s m () # listen :: RWST r w s m a -> RWST r w s m (a, w) # pass :: RWST r w s m (a, w -> w) -> RWST r w s m a #
(Monoid w, Monad m) => MonadWriter w (RWST r w s m)
Instance details Defined in Control.Monad.Writer.Class Methods writer :: (a, w) -> RWST r w s m a # tell :: w -> RWST r w s m () # listen :: RWST r w s m a -> RWST r w s m (a, w) # pass :: RWST r w s m (a, w -> w) -> RWST r w s m a #

listens :: 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)

censor :: 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)

type 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 >>= combines the outputs of the subcomputations using mappend.

runWriter :: Writer w a -> (a, w) #

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

execWriter :: Writer w a -> w #

Extract the output from a writer computation.

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

mapWriter :: ((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)

newtype 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 >>= combines the outputs of the subcomputations using mappend.

Constructors

WriterT
Fields runWriterT :: m (a, w)

Instances

(Monoid w, Monad m) => MonadWriter w (WriterT w m)
Instance details Defined in Control.Monad.Writer.Class Methods writer :: (a, w) -> WriterT w m a # tell :: w -> WriterT w m () # listen :: WriterT w m a -> WriterT w m (a, w) # pass :: WriterT w m (a, w -> w) -> WriterT w m a #
(Monoid w, MonadState s m) => MonadState s (WriterT w m)
Instance details Defined in Control.Monad.State.Class Methods get :: WriterT w m s # put :: s -> WriterT w m () # state :: (s -> (a, s)) -> WriterT w m a #
(Monoid w, MonadReader r m) => MonadReader r (WriterT w m)
Instance details Defined in Control.Monad.Reader.Class Methods ask :: WriterT w m r # local :: (r -> r) -> WriterT w m a -> WriterT w m a # reader :: (r -> a) -> WriterT w m a #
Monoid w => MonadTrans (WriterT w)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods lift :: Monad m => m a -> WriterT w m a #
(Monoid w, Monad m) => Monad (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods (>>=) :: WriterT w m a -> (a -> WriterT w m b) -> WriterT w m b # (>>) :: WriterT w m a -> WriterT w m b -> WriterT w m b # return :: a -> WriterT w m a # fail :: String -> WriterT w m a #
Functor m => Functor (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods fmap :: (a -> b) -> WriterT w m a -> WriterT w m b # (<$) :: a -> WriterT w m b -> WriterT w m a #
(Monoid w, MonadFix m) => MonadFix (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods mfix :: (a -> WriterT w m a) -> WriterT w m a #
(Monoid w, MonadFail m) => MonadFail (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods fail :: String -> WriterT w m a #
(Monoid w, Applicative m) => Applicative (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods pure :: a -> WriterT w m a # (<>) :: WriterT w m (a -> b) -> WriterT w m a -> WriterT w m b # liftA2 :: (a -> b -> c) -> WriterT w m a -> WriterT w m b -> WriterT w m c # (>) :: WriterT w m a -> WriterT w m b -> WriterT w m b # (<*) :: WriterT w m a -> WriterT w m b -> WriterT w m a #
Foldable f => Foldable (WriterT w f)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods fold :: Monoid m => WriterT w f m -> m # foldMap :: Monoid m => (a -> m) -> WriterT w f a -> m # foldr :: (a -> b -> b) -> b -> WriterT w f a -> b # foldr' :: (a -> b -> b) -> b -> WriterT w f a -> b # foldl :: (b -> a -> b) -> b -> WriterT w f a -> b # foldl' :: (b -> a -> b) -> b -> WriterT w f a -> b # foldr1 :: (a -> a -> a) -> WriterT w f a -> a # foldl1 :: (a -> a -> a) -> WriterT w f a -> a # toList :: WriterT w f a -> [a] # null :: WriterT w f a -> Bool # length :: WriterT w f a -> Int # elem :: Eq a => a -> WriterT w f a -> Bool # maximum :: Ord a => WriterT w f a -> a # minimum :: Ord a => WriterT w f a -> a # sum :: Num a => WriterT w f a -> a # product :: Num a => WriterT w f a -> a #
Traversable f => Traversable (WriterT w f)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods traverse :: Applicative f0 => (a -> f0 b) -> WriterT w f a -> f0 (WriterT w f b) # sequenceA :: Applicative f0 => WriterT w f (f0 a) -> f0 (WriterT w f a) # mapM :: Monad m => (a -> m b) -> WriterT w f a -> m (WriterT w f b) # sequence :: Monad m => WriterT w f (m a) -> m (WriterT w f a) #
Contravariant m => Contravariant (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods contramap :: (a -> b) -> WriterT w m b -> WriterT w m a # (>$) :: b -> WriterT w m b -> WriterT w m a #
(Eq w, Eq1 m) => Eq1 (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods liftEq :: (a -> b -> Bool) -> WriterT w m a -> WriterT w m b -> Bool #
(Ord w, Ord1 m) => Ord1 (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods liftCompare :: (a -> b -> Ordering) -> WriterT w m a -> WriterT w m b -> Ordering #
(Read w, Read1 m) => Read1 (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods liftReadsPrec :: (Int -> ReadS a) -> ReadS [a] -> Int -> ReadS (WriterT w m a) # liftReadList :: (Int -> ReadS a) -> ReadS [a] -> ReadS [WriterT w m a] # liftReadPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec (WriterT w m a) # liftReadListPrec :: ReadPrec a -> ReadPrec [a] -> ReadPrec [WriterT w m a] #
(Show w, Show1 m) => Show1 (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods liftShowsPrec :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> Int -> WriterT w m a -> ShowS # liftShowList :: (Int -> a -> ShowS) -> ([a] -> ShowS) -> [WriterT w m a] -> ShowS #
(Monoid w, MonadZip m) => MonadZip (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods mzip :: WriterT w m a -> WriterT w m b -> WriterT w m (a, b) # mzipWith :: (a -> b -> c) -> WriterT w m a -> WriterT w m b -> WriterT w m c # munzip :: WriterT w m (a, b) -> (WriterT w m a, WriterT w m b) #
(Monoid w, MonadIO m) => MonadIO (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods liftIO :: IO a -> WriterT w m a #
(Monoid w, Alternative m) => Alternative (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods empty :: WriterT w m a # (<\|>) :: WriterT w m a -> WriterT w m a -> WriterT w m a # some :: WriterT w m a -> WriterT w m [a] # many :: WriterT w m a -> WriterT w m [a] #
(Monoid w, MonadPlus m) => MonadPlus (WriterT w m)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods mzero :: WriterT w m a # mplus :: WriterT w m a -> WriterT w m a -> WriterT w m a #
(MonadThrow m, Monoid w) => MonadThrow (WriterT w m)
Instance details Defined in Control.Monad.Catch Methods throwM :: Exception e => e -> WriterT w m a #
(MonadCatch m, Monoid w) => MonadCatch (WriterT w m)
Instance details Defined in Control.Monad.Catch Methods catch :: Exception e => WriterT w m a -> (e -> WriterT w m a) -> WriterT w m a #
(MonadMask m, Monoid w) => MonadMask (WriterT w m)
Instance details Defined in Control.Monad.Catch Methods mask :: ((forall a. WriterT w m a -> WriterT w m a) -> WriterT w m b) -> WriterT w m b # uninterruptibleMask :: ((forall a. WriterT w m a -> WriterT w m a) -> WriterT w m b) -> WriterT w m b # generalBracket :: WriterT w m a -> (a -> ExitCase b -> WriterT w m c) -> (a -> WriterT w m b) -> WriterT w m (b, c) #
(Monoid w, PrimMonad m) => PrimMonad (WriterT w m)
Instance details Defined in Control.Monad.Primitive Associated Types type PrimState (WriterT w m) :: Type # Methods primitive :: (State# (PrimState (WriterT w m)) -> (#State# (PrimState (WriterT w m)), a#)) -> WriterT w m a #
(Eq w, Eq1 m, Eq a) => Eq (WriterT w m a)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods (==) :: WriterT w m a -> WriterT w m a -> Bool # (/=) :: WriterT w m a -> WriterT w m a -> Bool #
(Ord w, Ord1 m, Ord a) => Ord (WriterT w m a)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods compare :: WriterT w m a -> WriterT w m a -> Ordering # (<) :: WriterT w m a -> WriterT w m a -> Bool # (<=) :: WriterT w m a -> WriterT w m a -> Bool # (>) :: WriterT w m a -> WriterT w m a -> Bool # (>=) :: WriterT w m a -> WriterT w m a -> Bool # max :: WriterT w m a -> WriterT w m a -> WriterT w m a # min :: WriterT w m a -> WriterT w m a -> WriterT w m a #
(Read w, Read1 m, Read a) => Read (WriterT w m a)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods readsPrec :: Int -> ReadS (WriterT w m a) # readList :: ReadS [WriterT w m a] # readPrec :: ReadPrec (WriterT w m a) # readListPrec :: ReadPrec [WriterT w m a] #
(Show w, Show1 m, Show a) => Show (WriterT w m a)
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods showsPrec :: Int -> WriterT w m a -> ShowS # show :: WriterT w m a -> String # showList :: [WriterT w m a] -> ShowS #
type PrimState (WriterT w m)
Instance details Defined in Control.Monad.Primitive type PrimState (WriterT w m) = PrimState m

execWriterT :: Monad m => WriterT w m a -> m w #

Extract the output from a writer computation.

execWriterT m = liftM snd (runWriterT m)

mapWriterT :: (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)