Streamly.Internal.Data.Stream.Ahead

For AheadT streams:

(<>) = Streamly.Prelude.ahead
(>>=) = flip . Streamly.Prelude.concatMapWith Streamly.Prelude.ahead

A single Monad bind behaves like a for loop with iterations executed concurrently, ahead of time, producing side effects of iterations out of order, but results in order:

>>> :{Stream.toList $ Stream.fromAhead $ do     x <- Stream.fromList [2,1] -- foreach x in stream     Stream.fromEffect $ delay x:}1 sec2 sec[2,1]

Nested monad binds behave like nested for loops with nested iterations executed concurrently, ahead of time:

>>> :{Stream.toList $ Stream.fromAhead $ do    x <- Stream.fromList [1,2] -- foreach x in stream    y <- Stream.fromList [2,4] -- foreach y in stream    Stream.fromEffect $ delay (x + y):}3 sec4 sec5 sec6 sec[3,5,4,6]

The behavior can be explained as follows. All the iterations corresponding to the element 1 in the first stream constitute one output stream and all the iterations corresponding to 2 constitute another output stream and these two output streams are merged using ahead.

Since: 0.3.0 (Streamly)

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

Since: 0.3.0 (Streamly)

XXX we can implement it more efficienty by directly implementing instead of combining streams using ahead.