2-- Module : Streamly.Internal.Data.Stream.Transform
3-- Copyright : (c) 2017 Composewell Technologies
4-- License : BSD-3-Clause
5-- Maintainer : streamly@composewell.com
6-- Stability : experimental
9module Streamly.Internal.Data.Stream.Transform
12 -- | Pass through a 'Pipe'.
19 -- | Stateless one-to-one maps.
23 -- * Mapping Side Effects (Observation)
24 -- | See also the intersperse*_ combinators.
37 -- | Produce a subset of the stream using criteria based on the values of
38 -- the elements. We can use a concatMap and scan for filtering but these
39 -- combinators are more efficient and convenient.
41 -- mapMaybeM is a general filtering combinator as we can map the stream to
42 -- Just/Nothing using any stateful fold and then use this to filter out.
53 -- Stateful/scanning filters
60 -- | Produce a subset of the stream trimmed at ends.
74 -- * Position Indexing
85 , findIndices -- XXX indicesBy
86 , elemIndices -- XXX indicesOf
89 -- | Map using the previous element.
96 -- * Inserting Elements
97 -- | Produce a superset of the stream. This is the opposite of
98 -- filtering/sampling. We can always use concatMap and scan for inserting
99 -- but these combinators are more efficient and convenient.
101 -- Element agnostic (Opposite of sampling)
103 , intersperseM -- XXX naming
107 , intersperseMSuffixWith
109 -- , interspersePrefix
110 -- , interspersePrefixBySpan
112 -- * Inserting Side Effects/Time
113 , intersperseM_ -- XXX naming
115 , intersperseMSuffix_
117 , intersperseMPrefix_
120 -- * Element Aware Insertion
121 -- | Opposite of filtering
123 -- , intersperseByBefore
124 -- , intersperseByAfter
126 -- Fold and Unfold, Buffering
134 -- Move these to Streamly.Data.Either.Stream?
143import Control.Concurrent (threadDelay)
144import Control.Monad (void)
145import Control.Monad.IO.Class (MonadIO (liftIO))
146import Data.Either (fromLeft, isLeft, isRight, fromRight)
147import Data.Maybe (isJust, fromJust)
149import Streamly.Internal.Data.Fold.Type (Fold)
150import Streamly.Internal.Data.Pipe (Pipe)
151import Streamly.Internal.Data.Time.Units (AbsTime, RelTime64)
153import qualified Streamly.Internal.Data.Fold as FL
154-- import qualified Streamly.Internal.Data.Fold.Window as Window
155import qualified Streamly.Internal.Data.Stream.StreamD.Transform as D
156import qualified Streamly.Internal.Data.Stream.StreamD.Type as D
157import qualified Streamly.Internal.Data.Stream.StreamK.Type as K
160import Streamly.Internal.Data.Stream.Bottom
161import Streamly.Internal.Data.Stream.Type
164 ( filter, drop, dropWhile, take, takeWhile, foldr, map, mapM, sequence
165 , reverse, foldr1 , repeat, scanl, scanl1, zipWith)
170-- >>> import Control.Concurrent (threadDelay)
171-- >>> import Control.Monad (void)
172-- >>> import Control.Monad.IO.Class (MonadIO (liftIO))
173-- >>> import Data.Either (fromLeft, fromRight, isLeft, isRight, either)
174-- >>> import Data.Function ((&))
175-- >>> import Data.Maybe (fromJust, isJust)
176-- >>> import Prelude hiding (filter, drop, dropWhile, take, takeWhile, foldr, map, mapM, sequence, reverse, foldr1 , scanl, scanl1)
177-- >>> import Streamly.Internal.Data.Stream (Stream)
178-- >>> import qualified Streamly.Data.Fold as Fold
179-- >>> import qualified Streamly.Data.Unfold as Unfold
180-- >>> import qualified Streamly.Internal.Data.Fold as Fold (filtering)
181-- >>> import qualified Streamly.Internal.Data.Fold.Window as Window
182-- >>> import qualified Streamly.Internal.Data.Stream as Stream
183-- >>> import System.IO (stdout, hSetBuffering, BufferMode(LineBuffering))
185-- >>> hSetBuffering stdout LineBuffering
187-- XXX because of the use of D.cons for appending, folds and scans have
188-- quadratic complexity when iterated over a stream. We should use StreamK for
189-- linear performance on iteration.
191------------------------------------------------------------------------------
193------------------------------------------------------------------------------
195-- | Use a 'Pipe' to transform a stream.
199{-# INLINE transform #-}
200transform :: Monad m => Pipe m a b -> Stream m a -> Stream m b
201transform pipe xs = fromStreamD $ D.transform pipe (toStreamD xs)
203------------------------------------------------------------------------------
204-- Transformation Folds
205------------------------------------------------------------------------------
207-- | Right fold to a streaming monad.
209-- > foldrS Stream.cons Stream.nil === id
211-- 'foldrS' can be used to perform stateless stream to stream transformations
212-- like map and filter in general. It can be coupled with a scan to perform
213-- stateful transformations. However, note that the custom map and filter
214-- routines can be much more efficient than this due to better stream fusion.
216-- >>> input = Stream.fromList [1..5]
217-- >>> Stream.fold Fold.toList $ Stream.foldrS Stream.cons Stream.nil input
220-- Find if any element in the stream is 'True':
222-- >>> step x xs = if odd x then Stream.fromPure True else xs
223-- >>> input = Stream.fromList (2:4:5:undefined) :: Stream IO Int
224-- >>> Stream.fold Fold.toList $ Stream.foldrS step (Stream.fromPure False) input
227-- Map (+2) on odd elements and filter out the even elements:
229-- >>> step x xs = if odd x then (x + 2) `Stream.cons` xs else xs
230-- >>> input = Stream.fromList [1..5] :: Stream IO Int
231-- >>> Stream.fold Fold.toList $ Stream.foldrS step Stream.nil input
237 (a -> Stream m b -> Stream m b)
244 (\y ys -> toStreamK $ f y (fromStreamK ys))
248------------------------------------------------------------------------------
249-- Transformation by Mapping
250------------------------------------------------------------------------------
253-- >>> mapM f = Stream.sequence . fmap f
255-- Apply a monadic function to each element of the stream and replace it with
256-- the output of the resulting action.
258-- >>> s = Stream.fromList ["a", "b", "c"]
259-- >>> Stream.fold Fold.drain $ Stream.mapM putStr s
263mapM :: Monad m => (a -> m b) -> Stream m a -> Stream m b
264mapM f m = fromStreamK $ D.toStreamK $ D.mapM f $ toStreamD m
267-- >>> sequence = Stream.mapM id
269-- Replace the elements of a stream of monadic actions with the outputs of
272-- >>> s = Stream.fromList [putStr "a", putStr "b", putStrLn "c"]
273-- >>> Stream.fold Fold.drain $ Stream.sequence s
276{-# INLINE sequence #-}
277sequence :: Monad m => Stream m (m a) -> Stream m a
280------------------------------------------------------------------------------
281-- Mapping side effects
282------------------------------------------------------------------------------
284-- | Tap the data flowing through a stream into a 'Fold'. For example, you may
285-- add a tap to log the contents flowing through the stream. The fold is used
286-- only for effects, its result is discarded.
291-- -----stream m a ---------------stream m a-----
295-- >>> s = Stream.enumerateFromTo 1 2
296-- >>> Stream.fold Fold.drain $ Stream.tap (Fold.drainMapM print) s
300-- Compare with 'trace'.
303tap :: Monad m => FL.Fold m a b -> Stream m a -> Stream m a
304tap f xs = fromStreamD $ D.tap f (toStreamD xs)
306-- | Apply a monadic function to each element flowing through the stream and
307-- discard the results.
309-- >>> s = Stream.enumerateFromTo 1 2
310-- >>> Stream.fold Fold.drain $ Stream.trace print s
314-- Compare with 'tap'.
317trace :: Monad m => (a -> m b) -> Stream m a -> Stream m a
318trace f = mapM (\x -> void (f x) >> return x)
320-- | Perform a side effect before yielding each element of the stream and
321-- discard the results.
323-- >>> s = Stream.enumerateFromTo 1 2
324-- >>> Stream.fold Fold.drain $ Stream.trace_ (print "got here") s
328-- Same as 'intersperseMPrefix_' but always serial.
334trace_ :: Monad m => m b -> Stream m a -> Stream m a
335trace_ eff = fromStreamD . D.mapM (\x -> eff >> return x) . toStreamD
337-------------------------------------------------------------------------------
339-------------------------------------------------------------------------------
341-- | @scanlMAfter' accumulate initial done stream@ is like 'scanlM'' except
342-- that it provides an additional @done@ function to be applied on the
343-- accumulator when the stream stops. The result of @done@ is also emitted in
346-- This function can be used to allocate a resource in the beginning of the
347-- scan and release it when the stream ends or to flush the internal state of
348-- the scan at the end.
352{-# INLINE scanlMAfter' #-}
360scanlMAfter' step initial done stream =
361 fromStreamD $ D.scanlMAfter' step initial done $ toStreamD stream
363------------------------------------------------------------------------------
364-- Scanning with a Fold
365------------------------------------------------------------------------------
367-- XXX It may be useful to have a version of scan where we can keep the
368-- accumulator independent of the value emitted. So that we do not necessarily
369-- have to keep a value in the accumulator which we are not using. We can pass
370-- an extraction function that will take the accumulator and the current value
371-- of the element and emit the next value in the stream. That will also make it
372-- possible to modify the accumulator after using it. In fact, the step function
373-- can return new accumulator and the value to be emitted. The signature would
374-- be more like mapAccumL.
376-- | Strict left scan. Scan a stream using the given monadic fold.
378-- >>> s = Stream.fromList [1..10]
379-- >>> Stream.fold Fold.toList $ Stream.takeWhile (< 10) $ Stream.scan Fold.sum s
382-- See also: 'usingStateT'
386-- >>> scanl' step z = Stream.scan (Fold.foldl' step z)
388-- Like 'map', 'scanl'' too is a one to one transformation,
389-- however it adds an extra element.
391-- >>> s = Stream.fromList [1,2,3,4]
392-- >>> Stream.fold Fold.toList $ scanl' (+) 0 s
395-- >>> Stream.fold Fold.toList $ scanl' (flip (:)) [] s
396-- [[],[1],[2,1],[3,2,1],[4,3,2,1]]
398-- The output of 'scanl'' is the initial value of the accumulator followed by
399-- all the intermediate steps and the final result of 'foldl''.
401-- By streaming the accumulated state after each fold step, we can share the
402-- state across multiple stages of stream composition. Each stage can modify or
403-- extend the state, do some processing with it and emit it for the next stage,
404-- thus modularizing the stream processing. This can be useful in
405-- stateful or event-driven programming.
407-- Consider the following monolithic example, computing the sum and the product
408-- of the elements in a stream in one go using a @foldl'@:
410-- >>> foldl' step z = Stream.fold (Fold.foldl' step z)
411-- >>> foldl' (\(s, p) x -> (s + x, p * x)) (0,1) s
414-- Using @scanl'@ we can make it modular by computing the sum in the first
415-- stage and passing it down to the next stage for computing the product:
418-- foldl' (\(_, p) (s, x) -> (s, p * x)) (0,1)
419-- $ scanl' (\(s, _) x -> (s + x, x)) (0,1)
420-- $ Stream.fromList [1,2,3,4]
424-- IMPORTANT: 'scanl'' evaluates the accumulator to WHNF. To avoid building
425-- lazy expressions inside the accumulator, it is recommended that a strict
426-- data structure is used for accumulator.
429scan :: Monad m => Fold m a b -> Stream m a -> Stream m b
430scan fld m = fromStreamD $ D.scanOnce fld $ toStreamD m
432-- | Like 'scan' but restarts scanning afresh when the scanning fold
435{-# INLINE scanMany #-}
436scanMany :: Monad m => Fold m a b -> Stream m a -> Stream m b
437scanMany fld m = fromStreamD $ D.scanMany fld $ toStreamD m
439------------------------------------------------------------------------------
441------------------------------------------------------------------------------
443-- | Modify a @Stream m a -> Stream m a@ stream transformation that accepts a
444-- predicate @(a -> b)@ to accept @((s, a) -> b)@ instead, provided a
445-- transformation @Stream m a -> Stream m (s, a)@. Convenient to filter with
448-- >>> filterWithIndex = Stream.with Stream.indexed Stream.filter
453 (Stream m a -> Stream m (s, a))
454 -> (((s, a) -> b) -> Stream m (s, a) -> Stream m (s, a))
455 -> (((s, a) -> b) -> Stream m a -> Stream m a)
456with f comb g = fmap snd . comb g . f
458-- | Include only those elements that pass a predicate.
460-- >>> filter p = Stream.filterM (return . p)
461-- >>> filter p = Stream.mapMaybe (\x -> if p x then Just x else Nothing)
462-- >>> filter p = Stream.scanMaybe (Fold.filtering p)
465filter :: Monad m => (a -> Bool) -> Stream m a -> Stream m a
466-- filter p = scanMaybe (FL.filtering p)
467filter p m = fromStreamD $ D.filter p $ toStreamD m
469-- | Same as 'filter' but with a monadic predicate.
471-- >>> f p x = p x >>= \r -> return $ if r then Just x else Nothing
472-- >>> filterM p = Stream.mapMaybeM (f p)
474{-# INLINE filterM #-}
475filterM :: Monad m => (a -> m Bool) -> Stream m a -> Stream m a
476filterM p m = fromStreamD $ D.filterM p $ toStreamD m
478-- | Drop repeated elements that are adjacent to each other using the supplied
479-- comparison function.
481-- >>> uniq = Stream.uniqBy (==)
483-- To strip duplicate path separators:
485-- >>> input = Stream.fromList "//a//b"
486-- >>> f x y = x == '/' && y == '/'
487-- >>> Stream.fold Fold.toList $ Stream.uniqBy f input
496 (a -> a -> Bool) -> Stream m a -> Stream m a
497-- uniqBy eq = scanMaybe (FL.uniqBy eq)
498uniqBy eq = catMaybes . rollingMap f
505 Just x -> if x `eq` curr then Nothing else Just curr
507-- | Drop repeated elements that are adjacent to each other.
509-- >>> uniq = Stream.uniqBy (==)
512uniq :: (Eq a, Monad m) => Stream m a -> Stream m a
513-- uniq = scanMaybe FL.uniq
514uniq = fromStreamD . D.uniq . toStreamD
516-- | Strip all leading and trailing occurrences of an element passing a
517-- predicate and make all other consecutive occurrences uniq.
519-- >> prune p = Stream.dropWhileAround p $ Stream.uniqBy (x y -> p x && p y)
522-- > Stream.prune isSpace (Stream.fromList " hello world! ")
532 -- (Monad m, Eq a) =>
533 (a -> Bool) -> Stream m a -> Stream m a
534prune = error "Not implemented yet!"
536-- Possible implementation:
538-- Stream.catMaybes . Stream.parseMany (Parser.groupBy (==) Fold.repeated)@
540-- 'Fold.repeated' should return 'Just' when repeated, and 'Nothing' for a
543-- | Emit only repeated elements, once.
546repeated :: -- (Monad m, Eq a) =>
547 Stream m a -> Stream m a
550-- | Deletes the first occurrence of the element in the stream that satisfies
551-- the given equality predicate.
553-- >>> input = Stream.fromList [1,3,3,5]
554-- >>> Stream.fold Fold.toList $ Stream.deleteBy (==) 3 input
557{-# INLINE deleteBy #-}
558deleteBy :: Monad m => (a -> a -> Bool) -> a -> Stream m a -> Stream m a
559-- deleteBy cmp x = scanMaybe (FL.deleteBy cmp x)
560deleteBy cmp x m = fromStreamD $ D.deleteBy cmp x (toStreamD m)
562------------------------------------------------------------------------------
564------------------------------------------------------------------------------
566-- | Same as 'takeWhile' but with a monadic predicate.
568{-# INLINE takeWhileM #-}
569takeWhileM :: Monad m => (a -> m Bool) -> Stream m a -> Stream m a
570-- takeWhileM p = scanMaybe (FL.takingEndByM_ (\x -> not <$> p x))
571takeWhileM p m = fromStreamD $ D.takeWhileM p $ toStreamD m
573-- | Take all consecutive elements at the end of the stream for which the
576-- O(n) space, where n is the number elements taken.
579{-# INLINE takeWhileLast #-}
580takeWhileLast :: -- Monad m =>
581 (a -> Bool) -> Stream m a -> Stream m a
582takeWhileLast = undefined -- fromStreamD $ D.takeWhileLast n $ toStreamD m
584-- | Like 'takeWhile' and 'takeWhileLast' combined.
586-- O(n) space, where n is the number elements taken from the end.
589{-# INLINE takeWhileAround #-}
590takeWhileAround :: -- Monad m =>
591 (a -> Bool) -> Stream m a -> Stream m a
592takeWhileAround = undefined -- fromStreamD $ D.takeWhileAround n $ toStreamD m
594-- | Drop elements in the stream as long as the predicate succeeds and then
595-- take the rest of the stream.
597{-# INLINE dropWhile #-}
598dropWhile :: Monad m => (a -> Bool) -> Stream m a -> Stream m a
599-- dropWhile p = scanMaybe (FL.droppingWhile p)
600dropWhile p m = fromStreamD $ D.dropWhile p $ toStreamD m
602-- | Same as 'dropWhile' but with a monadic predicate.
604{-# INLINE dropWhileM #-}
605dropWhileM :: Monad m => (a -> m Bool) -> Stream m a -> Stream m a
606-- dropWhileM p = scanMaybe (FL.droppingWhileM p)
607dropWhileM p m = fromStreamD $ D.dropWhileM p $ toStreamD m
609-- | Drop @n@ elements at the end of the stream.
611-- O(n) space, where n is the number elements dropped.
614{-# INLINE dropLast #-}
615dropLast :: -- Monad m =>
616 Int -> Stream m a -> Stream m a
617dropLast = undefined -- fromStreamD $ D.dropLast n $ toStreamD m
619-- | Drop all consecutive elements at the end of the stream for which the
622-- O(n) space, where n is the number elements dropped.
625{-# INLINE dropWhileLast #-}
626dropWhileLast :: -- Monad m =>
627 (a -> Bool) -> Stream m a -> Stream m a
628dropWhileLast = undefined -- fromStreamD $ D.dropWhileLast n $ toStreamD m
630-- | Like 'dropWhile' and 'dropWhileLast' combined.
632-- O(n) space, where n is the number elements dropped from the end.
635{-# INLINE dropWhileAround #-}
636dropWhileAround :: -- Monad m =>
637 (a -> Bool) -> Stream m a -> Stream m a
638dropWhileAround = undefined -- fromStreamD $ D.dropWhileAround n $ toStreamD m
640------------------------------------------------------------------------------
642------------------------------------------------------------------------------
644-- | @insertBy cmp elem stream@ inserts @elem@ before the first element in
645-- @stream@ that is less than @elem@ when compared using @cmp@.
647-- >>> insertBy cmp x = Stream.mergeBy cmp (Stream.fromPure x)
649-- >>> input = Stream.fromList [1,3,5]
650-- >>> Stream.fold Fold.toList $ Stream.insertBy compare 2 input
653{-# INLINE insertBy #-}
654insertBy ::Monad m => (a -> a -> Ordering) -> a -> Stream m a -> Stream m a
655insertBy cmp x m = fromStreamD $ D.insertBy cmp x (toStreamD m)
657-- | Insert a pure value between successive elements of a stream.
659-- >>> input = Stream.fromList "hello"
660-- >>> Stream.fold Fold.toList $ Stream.intersperse ',' input
663{-# INLINE intersperse #-}
664intersperse :: Monad m => a -> Stream m a -> Stream m a
665intersperse a = fromStreamD . D.intersperse a . toStreamD
667-- | Insert a side effect before consuming an element of a stream except the
670-- >>> input = Stream.fromList "hello"
671-- >>> Stream.fold Fold.drain $ Stream.trace putChar $ Stream.intersperseM_ (putChar '.') input
675{-# INLINE intersperseM_ #-}
676intersperseM_ :: Monad m => m b -> Stream m a -> Stream m a
677intersperseM_ m = fromStreamD . D.intersperseM_ m . toStreamD
679-- | Intersperse a monadic action into the input stream after every @n@
682-- >> input = Stream.fromList "hello"
683-- >> Stream.fold Fold.toList $ Stream.intersperseMWith 2 (return ',') input
687{-# INLINE intersperseMWith #-}
688intersperseMWith :: -- Monad m =>
689 Int -> m a -> Stream m a -> Stream m a
690intersperseMWith _n _f _xs = undefined
692-- | Insert an effect and its output after consuming an element of a stream.
694-- >>> input = Stream.fromList "hello"
695-- >>> Stream.fold Fold.toList $ Stream.trace putChar $ Stream.intersperseMSuffix (putChar '.' >> return ',') input
696-- h.,e.,l.,l.,o.,"h,e,l,l,o,"
699{-# INLINE intersperseMSuffix #-}
700intersperseMSuffix :: Monad m => m a -> Stream m a -> Stream m a
701intersperseMSuffix m = fromStreamD . D.intersperseMSuffix m . toStreamD
703-- | Insert a side effect after consuming an element of a stream.
705-- >>> input = Stream.fromList "hello"
706-- >>> Stream.fold Fold.toList $ Stream.intersperseMSuffix_ (threadDelay 1000000) input
711{-# INLINE intersperseMSuffix_ #-}
712intersperseMSuffix_ :: Monad m => m b -> Stream m a -> Stream m a
713intersperseMSuffix_ m = fromStreamD . D.intersperseMSuffix_ m . toStreamD
715-- XXX Use an offset argument, like tapOffsetEvery
717-- | Like 'intersperseMSuffix' but intersperses an effectful action into the
718-- input stream after every @n@ elements and after the last element.
720-- >>> input = Stream.fromList "hello"
721-- >>> Stream.fold Fold.toList $ Stream.intersperseMSuffixWith 2 (return ',') input
726{-# INLINE intersperseMSuffixWith #-}
727intersperseMSuffixWith :: Monad m
728 => Int -> m a -> Stream m a -> Stream m a
729intersperseMSuffixWith n eff =
730 fromStreamD . D.intersperseMSuffixWith n eff . toStreamD
732-- | Insert a side effect before consuming an element of a stream.
736-- >>> intersperseMPrefix_ m = Stream.mapM (\x -> void m >> return x)
738-- >>> input = Stream.fromList "hello"
739-- >>> Stream.fold Fold.toList $ Stream.trace putChar $ Stream.intersperseMPrefix_ (putChar '.' >> return ',') input
746{-# INLINE intersperseMPrefix_ #-}
747intersperseMPrefix_ :: Monad m => m b -> Stream m a -> Stream m a
748intersperseMPrefix_ m = mapM (\x -> void m >> return x)
750------------------------------------------------------------------------------
752------------------------------------------------------------------------------
754-- XXX This should be in Prelude, should we export this as a helper function?
756-- | Block the current thread for specified number of seconds.
758sleep :: MonadIO m => Double -> m ()
759sleep n = liftIO $ threadDelay $ round $ n * 1000000
761-- | Introduce a delay of specified seconds between elements of the stream.
765-- >>> sleep n = liftIO $ threadDelay $ round $ n * 1000000
766-- >>> delay = Stream.intersperseM_ . sleep
770-- >>> input = Stream.enumerateFromTo 1 3
771-- >>> Stream.fold (Fold.drainMapM print) $ Stream.delay 1 input
777delay :: MonadIO m => Double -> Stream m a -> Stream m a
778delay = intersperseM_ . sleep
780-- | Introduce a delay of specified seconds after consuming an element of a
785-- >>> sleep n = liftIO $ threadDelay $ round $ n * 1000000
786-- >>> delayPost = Stream.intersperseMSuffix_ . sleep
790-- >>> input = Stream.enumerateFromTo 1 3
791-- >>> Stream.fold (Fold.drainMapM print) $ Stream.delayPost 1 input
798{-# INLINE delayPost #-}
799delayPost :: MonadIO m => Double -> Stream m a -> Stream m a
800delayPost n = intersperseMSuffix_ $ liftIO $ threadDelay $ round $ n * 1000000
802-- | Introduce a delay of specified seconds before consuming an element of a
807-- >>> sleep n = liftIO $ threadDelay $ round $ n * 1000000
808-- >>> delayPre = Stream.intersperseMPrefix_. sleep
812-- >>> input = Stream.enumerateFromTo 1 3
813-- >>> Stream.fold (Fold.drainMapM print) $ Stream.delayPre 1 input
820{-# INLINE delayPre #-}
821delayPre :: MonadIO m => Double -> Stream m a -> Stream m a
822delayPre = intersperseMPrefix_. sleep
824------------------------------------------------------------------------------
825-- Reorder in sequence
826------------------------------------------------------------------------------
828-- | Buffer until the next element in sequence arrives. The function argument
829-- determines the difference in sequence numbers. This could be useful in
830-- implementing sequenced streams, for example, TCP reassembly.
834{-# INLINE reassembleBy #-}
841reassembleBy = undefined
843------------------------------------------------------------------------------
845------------------------------------------------------------------------------
848-- >>> f = Fold.foldl' (\(i, _) x -> (i + 1, x)) (-1,undefined)
849-- >>> indexed = Stream.postscan f
850-- >>> indexed = Stream.zipWith (,) (Stream.enumerateFrom 0)
851-- >>> indexedR n = fmap (\(i, a) -> (n - i, a)) . indexed
853-- Pair each element in a stream with its index, starting from index 0.
855-- >>> Stream.fold Fold.toList $ Stream.indexed $ Stream.fromList "hello"
856-- [(0,'h'),(1,'e'),(2,'l'),(3,'l'),(4,'o')]
858{-# INLINE indexed #-}
859indexed :: Monad m => Stream m a -> Stream m (Int, a)
860-- indexed = scanMaybe FL.indexing
861indexed = fromStreamD . D.indexed . toStreamD
864-- >>> f n = Fold.foldl' (\(i, _) x -> (i - 1, x)) (n + 1,undefined)
865-- >>> indexedR n = Stream.postscan (f n)
867-- >>> s n = Stream.enumerateFromThen n (n - 1)
868-- >>> indexedR n = Stream.zipWith (,) (s n)
870-- Pair each element in a stream with its index, starting from the
871-- given index @n@ and counting down.
873-- >>> Stream.fold Fold.toList $ Stream.indexedR 10 $ Stream.fromList "hello"
874-- [(10,'h'),(9,'e'),(8,'l'),(7,'l'),(6,'o')]
876{-# INLINE indexedR #-}
877indexedR :: Monad m => Int -> Stream m a -> Stream m (Int, a)
878-- indexedR n = scanMaybe (FL.indexingRev n)
879indexedR n = fromStreamD . D.indexedR n . toStreamD
881-------------------------------------------------------------------------------
883-------------------------------------------------------------------------------
885-- Note: The timestamp stream must be the second stream in the zip so that the
886-- timestamp is generated after generating the stream element and not before.
887-- If we do not do that then the following example will generate the same
888-- timestamp for first two elements:
890-- Stream.fold Fold.toList $ Stream.timestamped $ Stream.delay $ Stream.enumerateFromTo 1 3
892-- | Pair each element in a stream with an absolute timestamp, using a clock of
893-- specified granularity. The timestamp is generated just before the element
896-- >>> Stream.fold Fold.toList $ Stream.timestampWith 0.01 $ Stream.delay 1 $ Stream.enumerateFromTo 1 3
897-- [(AbsTime (TimeSpec {sec = ..., nsec = ...}),1),(AbsTime (TimeSpec {sec = ..., nsec = ...}),2),(AbsTime (TimeSpec {sec = ..., nsec = ...}),3)]
901{-# INLINE timestampWith #-}
902timestampWith :: (MonadIO m)
903 => Double -> Stream m a -> Stream m (AbsTime, a)
904timestampWith g stream = zipWith (flip (,)) stream (absTimesWith g)
906-- TBD: check performance vs a custom implementation without using zipWith.
910{-# INLINE timestamped #-}
911timestamped :: (MonadIO m)
912 => Stream m a -> Stream m (AbsTime, a)
913timestamped = timestampWith 0.01
915-- | Pair each element in a stream with relative times starting from 0, using a
916-- clock with the specified granularity. The time is measured just before the
917-- element is consumed.
919-- >>> Stream.fold Fold.toList $ Stream.timeIndexWith 0.01 $ Stream.delay 1 $ Stream.enumerateFromTo 1 3
920-- [(RelTime64 (NanoSecond64 ...),1),(RelTime64 (NanoSecond64 ...),2),(RelTime64 (NanoSecond64 ...),3)]
924{-# INLINE timeIndexWith #-}
925timeIndexWith :: (MonadIO m)
926 => Double -> Stream m a -> Stream m (RelTime64, a)
927timeIndexWith g stream = zipWith (flip (,)) stream (relTimesWith g)
929-- | Pair each element in a stream with relative times starting from 0, using a
930-- 10 ms granularity clock. The time is measured just before the element is
933-- >>> Stream.fold Fold.toList $ Stream.timeIndexed $ Stream.delay 1 $ Stream.enumerateFromTo 1 3
934-- [(RelTime64 (NanoSecond64 ...),1),(RelTime64 (NanoSecond64 ...),2),(RelTime64 (NanoSecond64 ...),3)]
938{-# INLINE timeIndexed #-}
939timeIndexed :: (MonadIO m)
940 => Stream m a -> Stream m (RelTime64, a)
941timeIndexed = timeIndexWith 0.01
943------------------------------------------------------------------------------
945------------------------------------------------------------------------------
947-- | Find all the indices where the value of the element in the stream is equal
948-- to the given value.
950-- >>> elemIndices a = Stream.findIndices (== a)
952{-# INLINE elemIndices #-}
953elemIndices :: (Monad m, Eq a) => a -> Stream m a -> Stream m Int
954elemIndices a = findIndices (== a)
956------------------------------------------------------------------------------
958------------------------------------------------------------------------------
960-- XXX this is not a one-to-one map so calling it map may not be right.
961-- We can perhaps call it zipWithTail or rollWith.
963-- | Apply a function on every two successive elements of a stream. The first
964-- argument of the map function is the previous element and the second argument
965-- is the current element. When the current element is the first element, the
966-- previous element is 'Nothing'.
970{-# INLINE rollingMap #-}
971rollingMap :: Monad m => (Maybe a -> a -> b) -> Stream m a -> Stream m b
972-- rollingMap f = scanMaybe (FL.slide2 $ Window.rollingMap f)
973rollingMap f m = fromStreamD $ D.rollingMap f $ toStreamD m
975-- | Like 'rollingMap' but with an effectful map function.
979{-# INLINE rollingMapM #-}
980rollingMapM :: Monad m => (Maybe a -> a -> m b) -> Stream m a -> Stream m b
981-- rollingMapM f = scanMaybe (FL.slide2 $ Window.rollingMapM f)
982rollingMapM f m = fromStreamD $ D.rollingMapM f $ toStreamD m
984-- | Like 'rollingMap' but requires at least two elements in the stream,
985-- returns an empty stream otherwise.
987-- This is the stream equivalent of the list idiom @zipWith f xs (tail xs)@.
991{-# INLINE rollingMap2 #-}
992rollingMap2 :: Monad m => (a -> a -> b) -> Stream m a -> Stream m b
993rollingMap2 f m = fromStreamD $ D.rollingMap2 f $ toStreamD m
995------------------------------------------------------------------------------
997------------------------------------------------------------------------------
999-- | Map a 'Maybe' returning function to a stream, filter out the 'Nothing'
1000-- elements, and return a stream of values extracted from 'Just'.
1004-- >>> mapMaybe f = Stream.catMaybes . fmap f
1006{-# INLINE mapMaybe #-}
1007mapMaybe :: Monad m => (a -> Maybe b) -> Stream m a -> Stream m b
1008mapMaybe f m = fromStreamD $ D.mapMaybe f $ toStreamD m
1010-- | Like 'mapMaybe' but maps a monadic function.
1014-- >>> mapMaybeM f = Stream.catMaybes . Stream.mapM f
1016-- >>> mapM f = Stream.mapMaybeM (\x -> Just <$> f x)
1018{-# INLINE_EARLY mapMaybeM #-}
1020 => (a -> m (Maybe b)) -> Stream m a -> Stream m b
1021mapMaybeM f = fmap fromJust . filter isJust . mapM f
1023------------------------------------------------------------------------------
1025------------------------------------------------------------------------------
1027-- | Discard 'Right's and unwrap 'Left's in an 'Either' stream.
1029-- >>> catLefts = fmap (fromLeft undefined) . Stream.filter isLeft
1033{-# INLINE catLefts #-}
1034catLefts :: Monad m => Stream m (Either a b) -> Stream m a
1035catLefts = fmap (fromLeft undefined) . filter isLeft
1037-- | Discard 'Left's and unwrap 'Right's in an 'Either' stream.
1039-- >>> catRights = fmap (fromRight undefined) . Stream.filter isRight
1043{-# INLINE catRights #-}
1044catRights :: Monad m => Stream m (Either a b) -> Stream m b
1045catRights = fmap (fromRight undefined) . filter isRight
1047-- | Remove the either wrapper and flatten both lefts and as well as rights in
1048-- the output stream.
1050-- >>> catEithers = fmap (either id id)
1054{-# INLINE catEithers #-}
1055catEithers :: Monad m => Stream m (Either a a) -> Stream m a
1056catEithers = fmap (either id id)
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