Box.Emitter

Emitter wraps a producer destructor.

"Every Thought emits a Dice Throw" ~ Stéphane Mallarmé

Documentation

newtype Emitter m a

An Emitter emits values of type Maybe a. Source and producer are similar metaphors. An Emitter reaches into itself for the value to emit, where itself is an opaque thing from the pov of usage.

>>> e = Emitter (pure (Just "I'm emitted"))
>>> emit e
Just "I'm emitted"

>>> emit mempty
Nothing

Constructors

Emitter

Fields

• emit :: m (Maybe a)

Instances

FFunctor Emitter

Defined in Box.Emitter

Methods

foist :: (forall x. f x -> g x) -> Emitter f a -> Emitter g a

FoldableM Emitter

This fold completes on the first Nothing emitted, which may not be what you want.

Defined in Box.Emitter

Methods

foldrM :: Monad m => (a -> m b -> m b) -> m b -> Emitter m a -> m b

(Monad m, Alternative m) => Alternative (Emitter m)

Defined in Box.Emitter

Methods

empty :: Emitter m a

(<|>) :: Emitter m a -> Emitter m a -> Emitter m a

some :: Emitter m a -> Emitter m [a]

many :: Emitter m a -> Emitter m [a]

Applicative m => Applicative (Emitter m)

Defined in Box.Emitter

Methods

pure :: a -> Emitter m a

(<*>) :: Emitter m (a -> b) -> Emitter m a -> Emitter m b

liftA2 :: (a -> b -> c) -> Emitter m a -> Emitter m b -> Emitter m c

(*>) :: Emitter m a -> Emitter m b -> Emitter m b

(<*) :: Emitter m a -> Emitter m b -> Emitter m a

Functor m => Functor (Emitter m)

Defined in Box.Emitter

Methods

fmap :: (a -> b) -> Emitter m a -> Emitter m b

(<$) :: a -> Emitter m b -> Emitter m a

Monad m => Monad (Emitter m)

Defined in Box.Emitter

Methods

(>>=) :: Emitter m a -> (a -> Emitter m b) -> Emitter m b

(>>) :: Emitter m a -> Emitter m b -> Emitter m b

return :: a -> Emitter m a

(Alternative m, Monad m) => MonadPlus (Emitter m)

Defined in Box.Emitter

Methods

mzero :: Emitter m a

mplus :: Emitter m a -> Emitter m a -> Emitter m a

(Alternative m, Monad m) => Monoid (Emitter m a)

Defined in Box.Emitter

Methods

mempty :: Emitter m a

mappend :: Emitter m a -> Emitter m a -> Emitter m a

mconcat :: [Emitter m a] -> Emitter m a

(Alternative m, Monad m) => Semigroup (Emitter m a)

Defined in Box.Emitter

Methods

(<>) :: Emitter m a -> Emitter m a -> Emitter m a

sconcat :: NonEmpty (Emitter m a) -> Emitter m a

stimes :: Integral b => b -> Emitter m a -> Emitter m a

type CoEmitter m a = Codensity m (Emitter m a)

An Emitter continuation.

toListM :: Monad m => Emitter m a -> m [a]

Collect emits into a list, and close on the first Nothing.

>>> toListM <$|> qList [1..3]
[1,2,3]

witherE :: Monad m => (a -> m (Maybe b)) -> Emitter m a -> Emitter m b

A monadic Witherable

>>> toListM <$|> witherE (\x -> bool (print x >> pure Nothing) (pure (Just x)) (even x)) <$> (qList [1..3])
1
[]

filterE :: Monad m => (a -> m (Maybe b)) -> Emitter m a -> Emitter m b

Like witherE but does not emit Nothing on filtering.

>>> toListM <$|> filterE (\x -> bool (print x >> pure Nothing) (pure (Just x)) (even x)) <$> (qList [1..3])
1
3
[2]

readE :: (Functor m, Read a) => Emitter m Text -> Emitter m (Either Text a)

Read parse Emitter, returning the original text on error

>>> (toListM . readE) <$|> (qList ["1","2","3","four"]) :: IO [Either Text Int]
[Right 1,Right 2,Right 3,Left "four"]

unlistE :: Monad m => Emitter m [a] -> Emitter (StateT [a] m) a

Convert a list emitter to a (Stateful) element emitter.

>>> import Control.Monad.State.Lazy
>>> flip runStateT [] . toListM . unlistE <$|> (qList [[0..3],[5..7]])
([0,1,2,3,5,6,7],[])

takeE :: Monad m => Int -> Emitter m a -> Emitter (StateT Int m) a

Take n emits.

>>> import Control.Monad.State.Lazy
>>> flip evalStateT 0 <$|> toListM . takeE 4 <$> qList [0..]
[0,1,2,3]

takeUntilE :: Monad m => (a -> Bool) -> Emitter m a -> Emitter m a

Take from an emitter until a predicate.

>>> (toListM . takeUntilE (==3)) <$|> (qList [0..])
[0,1,2]

dropE :: Monad m => Int -> Emitter m a -> CoEmitter m a

Drop n emits.

>>> import Control.Monad.State.Lazy
>>> toListM <$|> (dropE 2 =<< qList [0..3])
[2,3]

pop :: Monad m => Emitter (StateT (Seq a) m) a

Pop from a State sequence.

>>> import qualified Data.Sequence as Seq
>>> import Control.Monad.State.Lazy (evalStateT)
>>> flip evalStateT (Seq.fromList [1..3]) $ toListM pop
[1,2,3]