An empty stream.

> toList nil
[]

Since: 0.1.0

Construct a stream by adding a pure value at the head of an existing stream. For serial streams this is the same as (return a) `consM` r but more efficient. For concurrent streams this is not concurrent whereas consM is concurrent. For example:

> toList $ 1 `cons` 2 `cons` 3 `cons` nil
[1,2,3]

Since: 0.1.0

Operator equivalent of cons.

> toList $ 1 .: 2 .: 3 .: nil
[1,2,3]

Since: 0.1.1

Constructs a stream by adding a monadic action at the head of an existing stream. For example:

> toList $ getLine `consM` getLine `consM` nil
hello
world
["hello","world"]

Concurrent (do not use parallely to construct infinite streams)

Since: 0.2.0

Operator equivalent of consM. We can read it as "parallel colon" to remember that | comes before :.

> toList $ getLine |: getLine |: nil
hello
world
["hello","world"]

let delay = threadDelay 1000000 >> print 1
drain $ serially  $ delay |: delay |: delay |: nil
drain $ parallely $ delay |: delay |: delay |: nil

Concurrent (do not use parallely to construct infinite streams)

Since: 0.2.0

yield a = a `cons` nil

Create a singleton stream from a pure value.

The following holds in monadic streams, but not in Zip streams:

yield = pure
yield = yieldM . pure

In Zip applicative streams yield is not the same as pure because in that case pure is equivalent to repeat instead. yield and pure are equally efficient, in other cases yield may be slightly more efficient than the other equivalent definitions.

Since: 0.4.0

yieldM m = m `consM` nil

Create a singleton stream from a monadic action.

> toList $ yieldM getLine
hello
["hello"]

Since: 0.4.0

Generate an infinite stream by repeating a pure value.

Since: 0.4.0

repeatM = fix . consM
repeatM = cycle1 . yieldM

Generate a stream by repeatedly executing a monadic action forever.

drain $ serially $ S.take 10 $ S.repeatM $ (threadDelay 1000000 >> print 1)
drain $ asyncly  $ S.take 10 $ S.repeatM $ (threadDelay 1000000 >> print 1)

Concurrent, infinite (do not use with parallely)

Since: 0.2.0

replicate = take n . repeat

Generate a stream of length n by repeating a value n times.

Since: 0.6.0

replicateM = take n . repeatM

Generate a stream by performing a monadic action n times. Same as:

drain $ serially $ S.replicateM 10 $ (threadDelay 1000000 >> print 1)
drain $ asyncly  $ S.replicateM 10 $ (threadDelay 1000000 >> print 1)

Concurrent

Since: 0.1.1

Types that can be enumerated as a stream. The operations in this type class are equivalent to those in the Enum type class, except that these generate a stream instead of a list. Use the functions in Streamly.Internal.Data.Stream.Enumeration module to define new instances.

Since: 0.6.0

enumerate = enumerateFrom minBound

Enumerate a Bounded type from its minBound to maxBound

Since: 0.6.0

enumerateTo = enumerateFromTo minBound

Enumerate a Bounded type from its minBound to specified value.

Since: 0.6.0

unfoldr step s =
    case step s of
        Nothing -> nil
        Just (a, b) -> a `cons` unfoldr step b

Build a stream by unfolding a pure step function step starting from a seed s. The step function returns the next element in the stream and the next seed value. When it is done it returns Nothing and the stream ends. For example,

let f b =
        if b > 3
        then Nothing
        else Just (b, b + 1)
in toList $ unfoldr f 0

[0,1,2,3]

Since: 0.1.0

Build a stream by unfolding a monadic step function starting from a seed. The step function returns the next element in the stream and the next seed value. When it is done it returns Nothing and the stream ends. For example,

let f b =
        if b > 3
        then return Nothing
        else print b >> return (Just (b, b + 1))
in drain $ unfoldrM f 0

 0
 1
 2
 3

When run concurrently, the next unfold step can run concurrently with the processing of the output of the previous step. Note that more than one step cannot run concurrently as the next step depends on the output of the previous step.

(asyncly $ S.unfoldrM (\n -> liftIO (threadDelay 1000000) >> return (Just (n, n + 1))) 0)
    & S.foldlM' (\_ a -> threadDelay 1000000 >> print a) ()

Concurrent

Since: 0.1.0

Convert an Unfold into a stream by supplying it an input seed.

>>> unfold (UF.replicateM 10) (putStrLn "hello")

Since: 0.7.0

iterate f x = x `cons` iterate f x

Generate an infinite stream with x as the first element and each successive element derived by applying the function f on the previous element.

> S.toList $ S.take 5 $ S.iterate (+1) 1
[1,2,3,4,5]

Since: 0.1.2

iterateM f m = m >>= a -> return a `consM` iterateM f (f a)

Generate an infinite stream with the first element generated by the action m and each successive element derived by applying the monadic function f on the previous element.

When run concurrently, the next iteration can run concurrently with the processing of the previous iteration. Note that more than one iteration cannot run concurrently as the next iteration depends on the output of the previous iteration.

drain $ serially $ S.take 10 $ S.iterateM
     (\x -> threadDelay 1000000 >> print x >> return (x + 1)) (return 0)

drain $ asyncly  $ S.take 10 $ S.iterateM
     (\x -> threadDelay 1000000 >> print x >> return (x + 1)) (return 0)

Concurrent

Since: 0.7.0 (signature change)

Since: 0.1.2

fromIndices f = let g i = f i `cons` g (i + 1) in g 0

Generate an infinite stream, whose values are the output of a function f applied on the corresponding index. Index starts at 0.

> S.toList $ S.take 5 $ S.fromIndices id
[0,1,2,3,4]

Since: 0.6.0

fromIndicesM f = let g i = f i `consM` g (i + 1) in g 0

Generate an infinite stream, whose values are the output of a monadic function f applied on the corresponding index. Index starts at 0.

Concurrent

Since: 0.6.0

fromList = foldr cons nil

Construct a stream from a list of pure values. This is more efficient than fromFoldable for serial streams.

Since: 0.4.0

fromListM = foldr consM nil

Construct a stream from a list of monadic actions. This is more efficient than fromFoldableM for serial streams.

Since: 0.4.0

fromFoldable = foldr cons nil

Construct a stream from a Foldable containing pure values:

Since: 0.2.0

fromFoldableM = foldr consM nil

Construct a stream from a Foldable containing monadic actions.

drain $ serially $ S.fromFoldableM $ replicateM 10 (threadDelay 1000000 >> print 1)
drain $ asyncly  $ S.fromFoldableM $ replicateM 10 (threadDelay 1000000 >> print 1)

Concurrent (do not use with parallely on infinite containers)

Since: 0.3.0

Decompose a stream into its head and tail. If the stream is empty, returns Nothing. If the stream is non-empty, returns Just (a, ma), where a is the head of the stream and ma its tail.

This is a brute force primitive. Avoid using it as long as possible, use it when no other combinator can do the job. This can be used to do pretty much anything in an imperative manner, as it just breaks down the stream into individual elements and we can loop over them as we deem fit. For example, this can be used to convert a streamly stream into other stream types.

Since: 0.1.0

tail = fmap (fmap snd) . uncons

Extract all but the first element of the stream, if any.

Since: 0.1.1

Extract all but the last element of the stream, if any.

Since: 0.5.0

Right associative/lazy pull fold. foldrM build final stream constructs an output structure using the step function build. build is invoked with the next input element and the remaining (lazy) tail of the output structure. It builds a lazy output expression using the two. When the "tail structure" in the output expression is evaluated it calls build again thus lazily consuming the input stream until either the output expression built by build is free of the "tail" or the input is exhausted in which case final is used as the terminating case for the output structure. For more details see the description in the previous section.

Example, determine if any element is odd in a stream:

>>> S.foldrM (\x xs -> if odd x then return True else xs) (return False) $ S.fromList (2:4:5:undefined)
> True

Since: 0.7.0 (signature changed)

Since: 0.2.0 (signature changed)

Since: 0.1.0

Right fold, lazy for lazy monads and pure streams, and strict for strict monads.

Please avoid using this routine in strict monads like IO unless you need a strict right fold. This is provided only for use in lazy monads (e.g. Identity) or pure streams. Note that with this signature it is not possible to implement a lazy foldr when the monad m is strict. In that case it would be strict in its accumulator and therefore would necessarily consume all its input.

Since: 0.1.0

Left associative/strict push fold. foldl' reduce initial stream invokes reduce with the accumulator and the next input in the input stream, using initial as the initial value of the current value of the accumulator. When the input is exhausted the current value of the accumulator is returned. Make sure to use a strict data structure for accumulator to not build unnecessary lazy expressions unless that's what you want. See the previous section for more details.

Since: 0.2.0

Strict left fold, for non-empty streams, using first element as the starting value. Returns Nothing if the stream is empty.

Since: 0.5.0

Like foldl' but with a monadic step function.

Since: 0.2.0

Fold a stream using the supplied left fold.

>>> S.fold FL.sum (S.enumerateFromTo 1 100)
5050

Since: 0.7.0

drain = mapM_ (\_ -> return ())

Run a stream, discarding the results. By default it interprets the stream as SerialT, to run other types of streams use the type adapting combinators for example drain . asyncly.

Since: 0.7.0

Extract the last element of the stream, if any.

last xs = xs !! (length xs - 1)

Since: 0.1.1

Determine the length of the stream.

Since: 0.1.0

Determine the sum of all elements of a stream of numbers. Returns 0 when the stream is empty. Note that this is not numerically stable for floating point numbers.

Since: 0.1.0

Determine the product of all elements of a stream of numbers. Returns 1 when the stream is empty.

Since: 0.1.1

Determine the maximum element in a stream using the supplied comparison function.

Since: 0.6.0

maximum = maximumBy compare

Determine the maximum element in a stream.

Since: 0.1.0

Determine the minimum element in a stream using the supplied comparison function.

Since: 0.6.0

minimum = minimumBy compare

Determine the minimum element in a stream.

Since: 0.1.0

Ensures that all the elements of the stream are identical and then returns that unique element.

Since: 0.6.0

toList = S.foldr (:) []

Convert a stream into a list in the underlying monad. The list can be consumed lazily in a lazy monad (e.g. Identity). In a strict monad (e.g. IO) the whole list is generated and buffered before it can be consumed.

Warning! working on large lists accumulated as buffers in memory could be very inefficient, consider using Streamly.Array instead.

Since: 0.1.0

drainN n = drain . take n

Run maximum up to n iterations of a stream.

Since: 0.7.0

drainWhile p = drain . takeWhile p

Run a stream as long as the predicate holds true.

Since: 0.7.0

Lookup the element at the given index.

Since: 0.6.0

Extract the first element of the stream, if any.

head = (!! 0)

Since: 0.1.0

Returns the first element that satisfies the given predicate.

Since: 0.6.0

Like findM but with a non-monadic predicate.

find p = findM (return . p)

Since: 0.5.0

In a stream of (key-value) pairs (a, b), return the value b of the first pair where the key equals the given value a.

lookup = snd <$> find ((==) . fst)

Since: 0.5.0

Returns the first index that satisfies the given predicate.

Since: 0.5.0

Returns the first index where a given value is found in the stream.

elemIndex a = findIndex (== a)

Since: 0.5.0

Determine whether the stream is empty.

Since: 0.1.1

Determine whether an element is present in the stream.

Since: 0.1.0

Determine whether an element is not present in the stream.

Since: 0.1.0

Determine whether all elements of a stream satisfy a predicate.

Since: 0.1.0

Determine whether any of the elements of a stream satisfy a predicate.

Since: 0.1.0

Determines if all elements of a boolean stream are True.

Since: 0.5.0

Determines whether at least one element of a boolean stream is True.

Since: 0.5.0

Compare two streams for equality using an equality function.

Since: 0.6.0

Compare two streams lexicographically using a comparison function.

Since: 0.6.0

Returns True if the first stream is the same as or a prefix of the second. A stream is a prefix of itself.

> S.isPrefixOf (S.fromList "hello") (S.fromList "hello" :: SerialT IO Char)
True

Since: 0.6.0

Returns True if all the elements of the first stream occur, in order, in the second stream. The elements do not have to occur consecutively. A stream is a subsequence of itself.

> S.isSubsequenceOf (S.fromList "hlo") (S.fromList "hello" :: SerialT IO Char)
True

Since: 0.6.0

Strip prefix if present and tell whether it was stripped or not. Returns Nothing if the stream does not start with the given prefix, stripped stream otherwise. Returns Just nil when the prefix is the same as the stream.

Space: O(1)

Since: 0.6.0

map = fmap

Same as fmap.

> S.toList $ S.map (+1) $ S.fromList [1,2,3]
[2,3,4]

Since: 0.4.0

sequence = mapM id

Replace the elements of a stream of monadic actions with the outputs of those actions.

> drain $ S.sequence $ S.fromList [putStr "a", putStr "b", putStrLn "c"]
abc

drain $ S.replicateM 10 (return $ threadDelay 1000000 >> print 1)
          & (serially . S.sequence)

drain $ S.replicateM 10 (return $ threadDelay 1000000 >> print 1)
          & (asyncly . S.sequence)

Concurrent (do not use with parallely on infinite streams)

Since: 0.1.0

mapM f = sequence . map f

Apply a monadic function to each element of the stream and replace it with the output of the resulting action.

> drain $ S.mapM putStr $ S.fromList ["a", "b", "c"]
abc

drain $ S.replicateM 10 (return 1)
          & (serially . S.mapM (\x -> threadDelay 1000000 >> print x))

drain $ S.replicateM 10 (return 1)
          & (asyncly . S.mapM (\x -> threadDelay 1000000 >> print x))

Concurrent (do not use with parallely on infinite streams)

Since: 0.1.0

mapM_ = drain . mapM

Apply a monadic action to each element of the stream and discard the output of the action. This is not really a pure transformation operation but a transformation followed by fold.

Since: 0.1.0

Apply a monadic function to each element flowing through the stream and discard the results.

> S.drain $ S.trace print (S.enumerateFromTo 1 2)
1
2

Compare with tap.

Since: 0.7.0

Tap the data flowing through a stream into a Fold. For example, you may add a tap to log the contents flowing through the stream. The fold is used only for effects, its result is discarded.

                  Fold m a b
                      |
-----stream m a ---------------stream m a-----

> S.drain $ S.tap (FL.drainBy print) (S.enumerateFromTo 1 2)
1
2

Compare with trace.

Since: 0.7.0

Strict left scan. Like map, scanl' too is a one to one transformation, however it adds an extra element.

> S.toList $ S.scanl' (+) 0 $ fromList [1,2,3,4]
[0,1,3,6,10]

> S.toList $ S.scanl' (flip (:)) [] $ S.fromList [1,2,3,4]
[[],[1],[2,1],[3,2,1],[4,3,2,1]]

The output of scanl' is the initial value of the accumulator followed by all the intermediate steps and the final result of foldl'.

By streaming the accumulated state after each fold step, we can share the state across multiple stages of stream composition. Each stage can modify or extend the state, do some processing with it and emit it for the next stage, thus modularizing the stream processing. This can be useful in stateful or event-driven programming.

Consider the following monolithic example, computing the sum and the product of the elements in a stream in one go using a foldl':

> S.foldl' (\(s, p) x -> (s + x, p * x)) (0,1) $ S.fromList [1,2,3,4]
(10,24)

Using scanl' we can make it modular by computing the sum in the first stage and passing it down to the next stage for computing the product:

>   S.foldl' (\(_, p) (s, x) -> (s, p * x)) (0,1)
  $ S.scanl' (\(s, _) x -> (s + x, x)) (0,1)
  $ S.fromList [1,2,3,4]
(10,24)

IMPORTANT: scanl' evaluates the accumulator to WHNF. To avoid building lazy expressions inside the accumulator, it is recommended that a strict data structure is used for accumulator.

Since: 0.2.0

Like scanl' but with a monadic fold function.

Since: 0.4.0

Like scanl' but does not stream the initial value of the accumulator.

postscanl' f z xs = S.drop 1 $ S.scanl' f z xs

Since: 0.7.0

Like postscanl' but with a monadic step function.

Since: 0.7.0

Like scanl' but for a non-empty stream. The first element of the stream is used as the initial value of the accumulator. Does nothing if the stream is empty.

> S.toList $ S.scanl1 (+) $ fromList [1,2,3,4]
[1,3,6,10]

Since: 0.6.0

Like scanl1' but with a monadic step function.

Since: 0.6.0

Scan a stream using the given monadic fold.

Since: 0.7.0

Postscan a stream using the given monadic fold.

Since: 0.7.0

Include only those elements that pass a predicate.

Since: 0.1.0

Same as filter but with a monadic predicate.

Since: 0.4.0

Map a Maybe returning function to a stream, filter out the Nothing elements, and return a stream of values extracted from Just.

Equivalent to:

mapMaybe f = S.map fromJust . S.filter isJust . S.map f

Since: 0.3.0

Like mapMaybe but maps a monadic function.

Equivalent to:

mapMaybeM f = S.map fromJust . S.filter isJust . S.mapM f

Concurrent (do not use with parallely on infinite streams)

Since: 0.3.0

Deletes the first occurrence of the element in the stream that satisfies the given equality predicate.

> S.toList $ S.deleteBy (==) 3 $ S.fromList [1,3,3,5]
[1,3,5]

Since: 0.6.0

Drop repeated elements that are adjacent to each other.

Since: 0.6.0

insertBy cmp elem stream inserts elem before the first element in stream that is less than elem when compared using cmp.

insertBy cmp x = mergeBy cmp (yield x)

> S.toList $ S.insertBy compare 2 $ S.fromList [1,3,5]
[1,2,3,5]

Since: 0.6.0

Generate a stream by inserting the result of a monadic action between consecutive elements of the given stream. Note that the monadic action is performed after the stream action before which its result is inserted.

> S.toList $ S.intersperseM (return ',') $ S.fromList "hello"
"h,e,l,l,o"

Since: 0.5.0

Generate a stream by inserting a given element between consecutive elements of the given stream.

> S.toList $ S.intersperse ',' $ S.fromList "hello"
"h,e,l,l,o"

Since: 0.7.0

indexed = S.postscanl' (\(i, _) x -> (i + 1, x)) (-1,undefined)
indexed = S.zipWith (,) (S.enumerateFrom 0)

Pair each element in a stream with its index, starting from index 0.

> S.toList $ S.indexed $ S.fromList "hello"
[(0,h),(1,e),(2,l),(3,l),(4,o)]

Since: 0.6.0

indexedR n = S.postscanl' (\(i, _) x -> (i - 1, x)) (n + 1,undefined)
indexedR n = S.zipWith (,) (S.enumerateFromThen n (n - 1))

Pair each element in a stream with its index, starting from the given index n and counting down.

> S.toList $ S.indexedR 10 $ S.fromList "hello"
[(10,h),(9,e),(8,l),(7,l),(6,o)]

Since: 0.6.0

Returns the elements of the stream in reverse order. The stream must be finite. Note that this necessarily buffers the entire stream in memory.

Since 0.7.0 (Monad m constraint)

Since: 0.1.1

Take first n elements from the stream and discard the rest.

Since: 0.1.0

End the stream as soon as the predicate fails on an element.

Since: 0.1.0

Same as takeWhile but with a monadic predicate.

Since: 0.4.0

Discard first n elements from the stream and take the rest.

Since: 0.1.0

Drop elements in the stream as long as the predicate succeeds and then take the rest of the stream.

Since: 0.1.0

Same as dropWhile but with a monadic predicate.

Since: 0.4.0

Group the input stream into groups of n elements each and then fold each group using the provided fold function.

> S.toList $ S.chunksOf 2 FL.sum (S.enumerateFromTo 1 10)
 [3,7,11,15,19]

This can be considered as an n-fold version of ltake where we apply ltake repeatedly on the leftover stream until the stream exhausts.

Since: 0.7.0

Group the input stream into windows of n second each and then fold each group using the provided fold function.

Since: 0.7.0

Find all the indices where the element in the stream satisfies the given predicate.

Since: 0.5.0

Find all the indices where the value of the element in the stream is equal to the given value.

Since: 0.5.0

Split on an infixed separator element, dropping the separator. Splits the stream on separator elements determined by the supplied predicate, separator is considered as infixed between two segments, if one side of the separator is missing then it is parsed as an empty stream. The supplied Fold is applied on the split segments. With - representing non-separator elements and . as separator, splitOn splits as follows:

"--.--" => "--" "--"
"--."   => "--" ""
".--"   => ""   "--"

splitOn (== x) is an inverse of intercalate (S.yield x)

Let's use the following definition for illustration:

splitOn' p xs = S.toList $ S.splitOn p (FL.toList) (S.fromList xs)

>>> splitOn' (== '.') ""
[""]

>>> splitOn' (== '.') "."
["",""]

>>> splitOn' (== '.') ".a"
> ["","a"]

>>> splitOn' (== '.') "a."
> ["a",""]

>>> splitOn' (== '.') "a.b"
> ["a","b"]

>>> splitOn' (== '.') "a..b"
> ["a","","b"]

Since: 0.7.0

Like splitOn but the separator is considered as suffixed to the segments in the stream. A missing suffix at the end is allowed. A separator at the beginning is parsed as empty segment. With - representing elements and . as separator, splitOnSuffix splits as follows:

 "--.--." => "--" "--"
 "--.--"  => "--" "--"
 ".--."   => "" "--"

splitOnSuffix' p xs = S.toList $ S.splitSuffixBy p (FL.toList) (S.fromList xs)

>>> splitOnSuffix' (== '.') ""
[]

>>> splitOnSuffix' (== '.') "."
[""]

>>> splitOnSuffix' (== '.') "a"
["a"]

>>> splitOnSuffix' (== '.') ".a"
> ["","a"]

>>> splitOnSuffix' (== '.') "a."
> ["a"]

>>> splitOnSuffix' (== '.') "a.b"
> ["a","b"]

>>> splitOnSuffix' (== '.') "a.b."
> ["a","b"]

>>> splitOnSuffix' (== '.') "a..b.."
> ["a","","b",""]

lines = splitOnSuffix (== '\n')

Since: 0.7.0

Like splitOnSuffix but keeps the suffix attached to the resulting splits.

splitWithSuffix' p xs = S.toList $ S.splitWithSuffix p (FL.toList) (S.fromList xs)

>>> splitWithSuffix' (== '.') ""
[]

>>> splitWithSuffix' (== '.') "."
["."]

>>> splitWithSuffix' (== '.') "a"
["a"]

>>> splitWithSuffix' (== '.') ".a"
> [".","a"]

>>> splitWithSuffix' (== '.') "a."
> ["a."]

>>> splitWithSuffix' (== '.') "a.b"
> ["a.","b"]

>>> splitWithSuffix' (== '.') "a.b."
> ["a.","b."]

>>> splitWithSuffix' (== '.') "a..b.."
> ["a.",".","b.","."]

Since: 0.7.0

Like splitOn after stripping leading, trailing, and repeated separators. Therefore, ".a..b." with . as the separator would be parsed as ["a","b"]. In other words, its like parsing words from whitespace separated text.

wordsBy' p xs = S.toList $ S.wordsBy p (FL.toList) (S.fromList xs)

>>> wordsBy' (== ',') ""
> []

>>> wordsBy' (== ',') ","
> []

>>> wordsBy' (== ',') ",a,,b,"
> ["a","b"]

words = wordsBy isSpace

Since: 0.7.0

groups = groupsBy (==)
groups = groupsByRolling (==)

Groups contiguous spans of equal elements together in individual groups.

>>> S.toList $ S.groups FL.toList $ S.fromList [1,1,2,2]
> [[1,1],[2,2]]

Since: 0.7.0

groupsBy cmp f $ S.fromList [a,b,c,...] assigns the element a to the first group, if a `cmp` b is True then b is also assigned to the same group. If a `cmp` c is True then c is also assigned to the same group and so on. When the comparison fails a new group is started. Each group is folded using the fold f and the result of the fold is emitted in the output stream.

>>> S.toList $ S.groupsBy (>) FL.toList $ S.fromList [1,3,7,0,2,5]
> [[1,3,7],[0,2,5]]

Since: 0.7.0

Unlike groupsBy this function performs a rolling comparison of two successive elements in the input stream. groupsByRolling cmp f $ S.fromList [a,b,c,...] assigns the element a to the first group, if a `cmp` b is True then b is also assigned to the same group. If b `cmp` c is True then c is also assigned to the same group and so on. When the comparison fails a new group is started. Each group is folded using the fold f.

>>> S.toList $ S.groupsByRolling (\a b -> a + 1 == b) FL.toList $ S.fromList [1,2,3,7,8,9]
> [[1,2,3],[7,8,9]]

Since: 0.7.0

Merge two streams using a comparison function. The head elements of both the streams are compared and the smaller of the two elements is emitted, if both elements are equal then the element from the first stream is used first.

If the streams are sorted in ascending order, the resulting stream would also remain sorted in ascending order.

> S.toList $ S.mergeBy compare (S.fromList [1,3,5]) (S.fromList [2,4,6,8])
[1,2,3,4,5,6,8]

Since: 0.6.0

Like mergeBy but with a monadic comparison function.

Merge two streams randomly:

> randomly _ _ = randomIO >>= x -> return $ if x then LT else GT
> S.toList $ S.mergeByM randomly (S.fromList [1,1,1,1]) (S.fromList [2,2,2,2])
[2,1,2,2,2,1,1,1]

Merge two streams in a proportion of 2:1:

proportionately m n = do
 ref <- newIORef $ cycle $ concat [replicate m LT, replicate n GT]
 return $ \_ _ -> do
     r <- readIORef ref
     writeIORef ref $ tail r
     return $ head r

main = do
 f <- proportionately 2 1
 xs <- S.toList $ S.mergeByM f (S.fromList [1,1,1,1,1,1]) (S.fromList [2,2,2])
 print xs

[1,1,2,1,1,2,1,1,2]

Since: 0.6.0

Like mergeBy but merges concurrently (i.e. both the elements being merged are generated concurrently).

Since: 0.6.0

Like mergeByM but merges concurrently (i.e. both the elements being merged are generated concurrently).

Since: 0.6.0

Zip two streams serially using a pure zipping function.

> S.toList $ S.zipWith (+) (S.fromList [1,2,3]) (S.fromList [4,5,6])
[5,7,9]

Since: 0.1.0

Like zipWith but using a monadic zipping function.

Since: 0.4.0

Like zipWith but zips concurrently i.e. both the streams being zipped are generated concurrently.

Since: 0.1.0

Like zipWithM but zips concurrently i.e. both the streams being zipped are generated concurrently.

Since: 0.4.0

concatMapWith merge map stream is a two dimensional looping combinator. The first argument specifies a merge or concat function that is used to merge the streams generated by applying the second argument i.e. the map function to each element of the input stream. The concat function could be serial, parallel, async, ahead or any other zip or merge function and the second argument could be any stream generation function using a seed.

Compare foldMapWith

Since: 0.7.0

Map a stream producing function on each element of the stream and then flatten the results into a single stream.

concatMap = concatMapWith serial
concatMap f = concatMapM (return . f)

Since: 0.6.0

Map a stream producing monadic function on each element of the stream and then flatten the results into a single stream. Since the stream generation function is monadic, unlike concatMap, it can produce an effect at the beginning of each iteration of the inner loop.

Since: 0.6.0

Like concatMap but uses an Unfold for stream generation. Unlike concatMap this can fuse the Unfold code with the inner loop and therefore provide many times better performance.

Since: 0.7.0

Run a side effect before the stream yields its first element.

Since: 0.7.0

Run a side effect whenever the stream stops normally.

Prefer afterIO over this as the after action in this combinator is not executed if the unfold is partially evaluated lazily and then garbage collected.

Since: 0.7.0

Run the first action before the stream starts and remember its output, generate a stream using the output, run the second action using the remembered value as an argument whenever the stream ends normally or due to an exception.

Prefer bracketIO over this as the after action in this combinator is not executed if the unfold is partially evaluated lazily and then garbage collected.

Since: 0.7.0

Run a side effect whenever the stream aborts due to an exception.

Since: 0.7.0

Run a side effect whenever the stream stops normally or aborts due to an exception.

Prefer finallyIO over this as the after action in this combinator is not executed if the unfold is partially evaluated lazily and then garbage collected.

Since: 0.7.0

When evaluating a stream if an exception occurs, stream evaluation aborts and the specified exception handler is run with the exception as argument.

Since: 0.7.0

Same as yieldM

Since: 0.2.0

Same as fromFoldable.

Since: 0.1.0

Strict left scan with an extraction function. Like scanl', but applies a user supplied extraction function (the third argument) at each step. This is designed to work with the foldl library. The suffix x is a mnemonic for extraction.

Since: 0.7.0 (Monad m constraint)

Since 0.2.0

Strict left fold with an extraction function. Like the standard strict left fold, but applies a user supplied extraction function (the third argument) to the folded value at the end. This is designed to work with the foldl library. The suffix x is a mnemonic for extraction.

Since: 0.2.0

Like foldx, but with a monadic step function.

Since: 0.2.0

Lazy right fold for non-empty streams, using first element as the starting value. Returns Nothing if the stream is empty.

Since: 0.5.0

Run a stream, discarding the results. By default it interprets the stream as SerialT, to run other types of streams use the type adapting combinators for example runStream . asyncly.

Since: 0.2.0

runN n = runStream . take n

Run maximum up to n iterations of a stream.

Since: 0.6.0

runWhile p = runStream . takeWhile p

Run a stream as long as the predicate holds true.

Since: 0.6.0

Read lines from an IO Handle into a stream of Strings.

Since: 0.1.0

toHandle h = S.mapM_ $ hPutStrLn h

Write a stream of Strings to an IO Handle.

Since: 0.1.0