rio-0.1.22.0: A standard library for Haskell

Safe Haskell | Safe-Inferred
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

Instances details

MonadWriter w m => MonadWriter w (CatchT m) |
Instance details Defined in Control.Monad.Catch.Pure Methods writer :: (a, w) -> CatchT m a # tell :: w -> CatchT m () # listen :: CatchT m a -> CatchT m (a, w) # pass :: CatchT m (a, w -> w) -> CatchT m a #
(Monoid w, HasWriteRef w env) => MonadWriter w (RIO env) # |
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) | 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', MonadWriter w m) => MonadWriter w (AccumT w' m)

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`.

Since: mtl-2.3

Instance details Defined in Control.Monad.Writer.Class Methods writer :: (a, w) -> AccumT w' m a # tell :: w -> AccumT w' m () # listen :: AccumT w' m a -> AccumT w' m (a, w) # pass :: AccumT w' m (a, w -> w) -> AccumT w' 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 #
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 (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 #
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 #
(Monoid w, Monad m) => MonadWriter w (WriterT w m) | Since: mtl-2.3
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 #
(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 (RWST r w s m) | Since: mtl-2.3
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 #
(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 `m `>>=` k` combines the outputs of the subcomputations using `mappend` (also known as `<>`):

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 `m `>>=` k` combines the outputs of the subcomputations using `mappend` (also known as `<>`):

Constructors

WriterT |

Fields

- runWriterT :: m (a, w)

#### Instances

Instances details

(MonadAccum w' m, Monoid w) => MonadAccum w' (WriterT w m) | Since: mtl-2.3
Instance details Defined in Control.Monad.Accum Methods look :: WriterT w m w' # add :: w' -> WriterT w m () # accum :: (w' -> (a, w')) -> WriterT w m a #
(Monoid w, MonadError e m) => MonadError e (WriterT w m) |
Instance details Defined in Control.Monad.Error.Class Methods throwError :: e -> WriterT w m a # catchError :: WriterT w m a -> (e -> WriterT w m a) -> 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 #

(MonadSelect w' m, Monoid w) => MonadSelect w' (WriterT w m)

'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).

Since: mtl-2.3

Instance details Defined in Control.Monad.Select Methods select :: ((a -> w') -> a) -> 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, 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 => MonadTrans (WriterT w) |
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods lift :: Monad m => m a -> WriterT w m a #
(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, 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) #
(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 #
Contravariant m => Contravariant (WriterT w m) |
Instance details Defined in Control.Monad.Trans.Writer.Lazy Methods contramap :: (a' -> a) -> WriterT w m a -> WriterT w m a' # (>$) :: b -> WriterT w m b -> WriterT w m a #
(MonadCatch m, Monoid w) => MonadCatch (WriterT w m) |
Instance details Defined in Control.Monad.Catch Methods catch :: (HasCallStack, 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 :: HasCallStack => ((forall a. WriterT w m a -> WriterT w m a) -> WriterT w m b) -> WriterT w m b #

uninterruptibleMask :: HasCallStack => ((forall a. WriterT w m a -> WriterT w m a) -> WriterT w m b) -> WriterT w m b #

generalBracket :: HasCallStack => WriterT w m a -> (a -> ExitCase b -> WriterT w m c) -> (a -> WriterT w m b) -> WriterT w m (b, c) #

(MonadThrow m, Monoid w) => MonadThrow (WriterT w m) |
Instance details Defined in Control.Monad.Catch Methods throwM :: (HasCallStack, Exception e) => e -> 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, 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 #
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, 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 #
(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 #
(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, 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 #
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 #

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) #
(Monoid w, MonadCont m) => MonadCont (WriterT w m) |
Instance details Defined in Control.Monad.Cont.Class Methods callCC :: ((a -> WriterT w m b) -> WriterT w m a) -> WriterT w m a #
(Monoid w, PrimMonad m) => PrimMonad (WriterT w m) |

Instance details

Defined in Control.Monad.Primitive

Associated Types

type PrimState (WriterT w m) |
Instance details Defined in Control.Monad.Primitive type PrimState (WriterT w m) = PrimState m

Methods

primitive :: (State# (PrimState (WriterT w m)) -> (# State# (PrimState (WriterT w m)), a #)) -> WriterT w m a #

(Monoid w, Zoom m n s t) => Zoom (WriterT w m) (WriterT w n) s t |
Instance details Defined in Lens.Micro.Mtl.Internal Methods zoom :: LensLike' (Zoomed (WriterT w m) c) t s -> WriterT w m c -> WriterT w n c #
Generic (WriterT w m a) |

Instance details

Defined in Control.Monad.Trans.Writer.Lazy

Associated Types

type Rep (WriterT w m a) |
Instance details Defined in Control.Monad.Trans.Writer.Lazy type Rep (WriterT w m a) = D1 ('MetaData "WriterT" "Control.Monad.Trans.Writer.Lazy" "transformers-0.6.1.1-inplace" 'True) (C1 ('MetaCons "WriterT" 'PrefixI 'True) (S1 ('MetaSel ('Just "runWriterT") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 (m (a, w)))))

Methods

from :: WriterT w m a -> Rep (WriterT w m a) x #

to :: Rep (WriterT w m a) x -> 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 #
(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 #

type Zoomed (WriterT w m) |
Instance details Defined in Lens.Micro.Mtl.Internal type Zoomed (WriterT w m) = FocusingPlus w (Zoomed m)
type PrimState (WriterT w m) |
Instance details Defined in Control.Monad.Primitive type PrimState (WriterT w m) = PrimState m
type Rep (WriterT w m a) |
Instance details Defined in Control.Monad.Trans.Writer.Lazy type Rep (WriterT w m a) = D1 ('MetaData "WriterT" "Control.Monad.Trans.Writer.Lazy" "transformers-0.6.1.1-inplace" 'True) (C1 ('MetaCons "WriterT" 'PrefixI 'True) (S1 ('MetaSel ('Just "runWriterT") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 (m (a, w)))))

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)