Streamly.Internal.Data.Stream.Ahead

Documentation

data AheadT m a

The Semigroup operation for AheadT appends two streams. The combined stream behaves like a single stream with the actions from the second stream appended to the first stream. The combined stream is evaluated in the speculative style. This operation can be used to fold an infinite lazy container of streams.

import Streamly
import qualified Streamly.Prelude as S
import Control.Concurrent

main = do
 xs <- S.toList . aheadly $ (p 1 |: p 2 |: nil) <> (p 3 |: p 4 |: nil)
 print xs
 where p n = threadDelay 1000000 >> return n

[1,2,3,4]

Any exceptions generated by a constituent stream are propagated to the output stream.

The monad instance of AheadT may run each monadic continuation (bind) concurrently in a speculative manner, performing side effects in a partially ordered manner but producing the outputs in an ordered manner like SerialT.

main = S.drain . aheadly $ do
    n <- return 3 <> return 2 <> return 1
    S.yieldM $ do
         threadDelay (n * 1000000)
         myThreadId >>= \tid -> putStrLn (show tid ++ ": Delay " ++ show n)

ThreadId 40: Delay 1
ThreadId 39: Delay 2
ThreadId 38: Delay 3

Since: 0.3.0

Instances

MonadTrans AheadT

Defined in Streamly.Internal.Data.Stream.Ahead

Methods

lift :: Monad m => m a -> AheadT m a

IsStream AheadT

Defined in Streamly.Internal.Data.Stream.Ahead

Methods

toStream :: AheadT m a -> Stream m a

fromStream :: Stream m a -> AheadT m a

consM :: MonadAsync m => m a -> AheadT m a -> AheadT m a

(|:) :: MonadAsync m => m a -> AheadT m a -> AheadT m a

(MonadBase b m, Monad m, MonadAsync m) => MonadBase b (AheadT m)

Defined in Streamly.Internal.Data.Stream.Ahead

Methods

liftBase :: b α -> AheadT m α

(MonadState s m, MonadAsync m) => MonadState s (AheadT m)

Defined in Streamly.Internal.Data.Stream.Ahead

Methods

get :: AheadT m s

put :: s -> AheadT m ()

state :: (s -> (a, s)) -> AheadT m a

(MonadReader r m, MonadAsync m) => MonadReader r (AheadT m)

Defined in Streamly.Internal.Data.Stream.Ahead

Methods

ask :: AheadT m r

local :: (r -> r) -> AheadT m a -> AheadT m a

reader :: (r -> a) -> AheadT m a

MonadAsync m => Monad (AheadT m)

Defined in Streamly.Internal.Data.Stream.Ahead

Methods

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

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

return :: a -> AheadT m a

fail :: String -> AheadT m a

Monad m => Functor (AheadT m)

Defined in Streamly.Internal.Data.Stream.Ahead

Methods

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

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

(Monad m, MonadAsync m) => Applicative (AheadT m)

Defined in Streamly.Internal.Data.Stream.Ahead

Methods

pure :: a -> AheadT m a

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

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

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

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

(MonadIO m, MonadAsync m) => MonadIO (AheadT m)

Defined in Streamly.Internal.Data.Stream.Ahead

Methods

liftIO :: IO a -> AheadT m a

(MonadThrow m, MonadAsync m) => MonadThrow (AheadT m)

Defined in Streamly.Internal.Data.Stream.Ahead

Methods

throwM :: Exception e => e -> AheadT m a

MonadAsync m => Semigroup (AheadT m a)

Defined in Streamly.Internal.Data.Stream.Ahead

Methods

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

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

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

MonadAsync m => Monoid (AheadT m a)

Defined in Streamly.Internal.Data.Stream.Ahead

Methods

mempty :: AheadT m a

mappend :: AheadT m a -> AheadT m a -> AheadT m a

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

type Ahead = AheadT IO

A serial IO stream of elements of type a with concurrent lookahead. See AheadT documentation for more details.

Since: 0.3.0

aheadly :: IsStream t => AheadT m a -> t m a

Fix the type of a polymorphic stream as AheadT.

Since: 0.3.0

ahead :: (IsStream t, MonadAsync m) => t m a -> t m a -> t m a

Polymorphic version of the Semigroup operation <> of AheadT. Merges two streams sequentially but with concurrent lookahead.

Since: 0.3.0