Data.Automaton.Trans.Writer

An Automaton with a WriterT layer outputs an extra monoid value on every step.

It is based on the strict writer monad Strict, so when combining it with other modules such as mtl's, the strict version has to be included, i.e. Strict instead of Writer or Lazy.

Documentation

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

MFunctor (WriterT w :: (Type -> Type) -> Type -> Type)

Defined in Control.Monad.Morph

Methods

hoist :: forall m n (b :: k). Monad m => (forall a. m a -> n a) -> WriterT w m b -> WriterT w n b

(Monoid w, MonadSplit g m) => MonadSplit g (WriterT w m)

Defined in Control.Monad.Random.Class

Methods

getSplit :: WriterT w m g

Monoid w => MMonad (WriterT w)

Defined in Control.Monad.Morph

Methods

embed :: forall (n :: Type -> Type) m b. Monad n => (forall a. m a -> WriterT w n a) -> WriterT w m b -> WriterT w n b

Monoid w => MonadTrans (WriterT w)

Defined in Control.Monad.Trans.Writer.Strict

Methods

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

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

Defined in Control.Monad.Random.Class

Methods

interleave :: WriterT w m a -> WriterT w m a

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

Defined in Control.Monad.Random.Class

Methods

getRandomR :: Random a => (a, a) -> WriterT w m a

getRandom :: Random a => WriterT w m a

getRandomRs :: Random a => (a, a) -> WriterT w m [a]

getRandoms :: Random a => WriterT w m [a]

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

Defined in Control.Monad.Trans.Writer.Strict

Methods

fail :: String -> WriterT w m a

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

Defined in Control.Monad.Trans.Writer.Strict

Methods

mfix :: (a -> WriterT w m a) -> WriterT w m a

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

Defined in Control.Monad.Trans.Writer.Strict

Methods

liftIO :: IO a -> WriterT w m a

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

Defined in Control.Monad.Trans.Writer.Strict

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)

Foldable f => Foldable (WriterT w f)

Defined in Control.Monad.Trans.Writer.Strict

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

(Eq w, Eq1 m) => Eq1 (WriterT w m)

Defined in Control.Monad.Trans.Writer.Strict

Methods

liftEq :: (a -> b -> Bool) -> WriterT w m a -> WriterT w m b -> Bool

(Ord w, Ord1 m) => Ord1 (WriterT w m)

Defined in Control.Monad.Trans.Writer.Strict

Methods

liftCompare :: (a -> b -> Ordering) -> WriterT w m a -> WriterT w m b -> Ordering

(Read w, Read1 m) => Read1 (WriterT w m)

Defined in Control.Monad.Trans.Writer.Strict

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)

Defined in Control.Monad.Trans.Writer.Strict

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)

Defined in Control.Monad.Trans.Writer.Strict

Methods

contramap :: (a' -> a) -> WriterT w m a -> WriterT w m a'

(>$) :: b -> WriterT w m b -> WriterT w m a

Traversable f => Traversable (WriterT w f)

Defined in Control.Monad.Trans.Writer.Strict

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

Defined in Control.Monad.Trans.Writer.Strict

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)

Defined in Control.Monad.Trans.Writer.Strict

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)

Defined in Control.Monad.Trans.Writer.Strict

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)

Defined in Control.Monad.Trans.Writer.Strict

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)

Defined in Control.Monad.Trans.Writer.Strict

Methods

mzero :: WriterT w m a

mplus :: WriterT w m a -> WriterT w m a -> WriterT w m a

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

Defined in Control.Monad.Primitive

Associated Types

type PrimState (WriterT w m)

Methods

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

(Monoid w, Selective f) => Selective (WriterT w f)

Defined in Control.Selective

Methods

select :: WriterT w f (Either a b) -> WriterT w f (a -> b) -> WriterT w f b

Generic (WriterT w m a)

Defined in Control.Monad.Trans.Writer.Strict

Associated Types

type Rep (WriterT w m a) :: Type -> Type

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)

Defined in Control.Monad.Trans.Writer.Strict

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)

Defined in Control.Monad.Trans.Writer.Strict

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)

Defined in Control.Monad.Trans.Writer.Strict

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)

Defined in Control.Monad.Trans.Writer.Strict

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 PrimState (WriterT w m)

Defined in Control.Monad.Primitive

type PrimState (WriterT w m) = PrimState m

type Rep (WriterT w m a)

Defined in Control.Monad.Trans.Writer.Strict

type Rep (WriterT w m a) = D1 ('MetaData "WriterT" "Control.Monad.Trans.Writer.Strict" "transformers-0.6.1.0" 'True) (C1 ('MetaCons "WriterT" 'PrefixI 'True) (S1 ('MetaSel ('Just "runWriterT") 'NoSourceUnpackedness 'NoSourceStrictness 'DecidedLazy) (Rec0 (m (a, w)))))

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.

tell :: forall (m :: Type -> Type) w. Monad m => w -> WriterT w m ()

tell w is an action that produces the output w.

listen :: forall (m :: Type -> Type) w a. Monad m => WriterT w m a -> WriterT w m (a, w)

listen m is an action that executes the action m and adds its output to the value of the computation.

• runWriterT (listen m) = liftM (\ (a, w) -> ((a, w), w)) (runWriterT m)

listens :: forall (m :: Type -> Type) w b a. Monad m => (w -> b) -> WriterT w m a -> WriterT w 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)

• runWriterT (listens f m) = liftM (\ (a, w) -> ((a, f w), w)) (runWriterT m)

censor :: forall (m :: Type -> Type) w a. Monad m => (w -> w) -> WriterT w m a -> WriterT w 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)

• runWriterT (censor f m) = liftM (\ (a, w) -> (a, f w)) (runWriterT m)

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)

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)

writer :: forall (m :: Type -> Type) a w. Monad m => (a, w) -> WriterT w m a

Construct a writer computation from a (result, output) pair. (The inverse of runWriter.)

writerS :: (Functor m, Monad m, Monoid w) => Automaton m a (w, b) -> Automaton (WriterT w m) a b

Convert an extra log output into a WriterT effect.

This is the opposite of runWriterS.

runWriterS :: (Functor m, Monad m) => Automaton (WriterT w m) a b -> Automaton m a (w, b)

Convert a WriterT effect into an extra log output.

This is the opposite of writerS.