{-| The names exported by this module are closely modeled on those in @Prelude@ and @Data.List@, but also on , and . The module may be said to give independent expression to the conception of Producer \/ Source \/ Generator manipulation articulated in the latter two modules. Because we dispense with piping and conduiting, the distinction between all of these modules collapses. Some things are lost but much is gained: on the one hand, everything comes much closer to ordinary beginning Haskell programming and, on the other, acquires the plasticity of programming directly with a general free monad type. The leading type, @Stream (Of a) m r@ is chosen to permit an api that is as close as possible to that of @Data.List@ and the @Prelude@. Import qualified thus: > import Streaming > import qualified Streaming.Prelude as S For the examples below, one sometimes needs > import Streaming.Prelude (each, yield, next, mapped, stdoutLn, stdinLn) > import Data.Function ((&)) Other libraries that come up in passing are > import qualified Control.Foldl as L -- cabal install foldl > import qualified Pipes as P > import qualified Pipes.Prelude as P > import qualified System.IO as IO Here are some correspondences between the types employed here and elsewhere: > streaming | pipes | conduit | io-streams > ------------------------------------------------------------------------------------------------------------------- > Stream (Of a) m () | Producer a m () | Source m a | InputStream a > | ListT m a | ConduitM () o m () | Generator r () > ------------------------------------------------------------------------------------------------------------------- > Stream (Of a) m r | Producer a m r | ConduitM () o m r | Generator a r > ------------------------------------------------------------------------------------------------------------------- > Stream (Of a) m (Stream (Of a) m r) | Producer a m (Producer a m r) | > -------------------------------------------------------------------------------------------------------------------- > Stream (Stream (Of a) m) r | FreeT (Producer a m) m r | > -------------------------------------------------------------------------------------------------------------------- > -------------------------------------------------------------------------------------------------------------------- > ByteString m () | Producer ByteString m () | Source m ByteString | InputStream ByteString > -------------------------------------------------------------------------------------------------------------------- > -} {-# LANGUAGE BangPatterns #-} {-# LANGUAGE CPP #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE TypeFamilies #-} module Streaming.Prelude ( -- * Types Of (..) -- * Introducing streams of elements -- $producers , yield , each , stdinLn , readLn , fromHandle , readFile , iterate , iterateM , repeat , repeatM , replicate , untilLeft , untilRight , cycle , replicateM , enumFrom , enumFromThen , unfoldr -- * Consuming streams of elements -- $consumers , stdoutLn , stdoutLn' , mapM_ , print , toHandle , writeFile , effects , erase , drained -- * Stream transformers -- $pipes , map , mapM , maps , mapsPost , mapped , mappedPost , for , with , subst , copy , duplicate , store , chain , sequence , nubOrd , nubOrdOn , nubInt , nubIntOn , filter , filterM , mapMaybeM , delay , intersperse , take , takeWhile -- , takeWhile' , takeWhileM , drop , dropWhile , concat -- , elemIndices -- , findIndices , scan , scanM , scanned , read , show , cons , slidingWindow , wrapEffect -- * Splitting and inspecting streams of elements , next , uncons , splitAt , split , breaks , break , breakWhen , span , group , groupBy -- , groupedBy -- * Sum and Compose manipulation , distinguish , switch , separate , unseparate , eitherToSum , sumToEither , sumToCompose , composeToSum -- * Folds -- $folds , fold , fold_ , foldM , foldM_ , foldMap , foldMap_ , all , all_ , any , any_ , sum , sum_ , product , product_ , head , head_ , last , last_ , elem , elem_ , notElem , notElem_ , length , length_ , toList , toList_ , mconcat , mconcat_ , minimum , minimum_ , maximum , maximum_ , foldrM , foldrT -- , all -- , any -- , and -- , or -- , elem -- , find -- , findIndex -- , head -- , index -- , last -- , length -- , maximum -- , minimum -- , null -- * Zips and unzips , zip , zipWith , zip3 , zipWith3 , unzip , partitionEithers , partition -- * Merging streams -- $merging , merge , mergeOn , mergeBy -- * Maybes -- $maybes , catMaybes , mapMaybe -- * Pair manipulation , lazily , strictly , fst' , snd' , mapOf , _first , _second -- * Interoperation , reread -- * Basic Type , Stream ) where import Streaming.Internal import Control.Applicative (Applicative (..)) import Control.Concurrent (threadDelay) import Control.Exception (throwIO, try) import Control.Monad hiding (filterM, mapM, mapM_, foldM, foldM_, replicateM, sequence) import Control.Monad.Trans import Data.Functor (Functor (..), (<$)) import Data.Functor.Compose import Data.Functor.Identity import Data.Functor.Of import Data.Functor.Sum import Data.Monoid (Monoid (mappend, mempty)) import Data.Ord (Ordering (..), comparing) import Foreign.C.Error (Errno(Errno), ePIPE) import Text.Read (readMaybe) import qualified Data.Foldable as Foldable import qualified Data.IntSet as IntSet import qualified Data.Sequence as Seq import qualified Data.Set as Set import qualified GHC.IO.Exception as G import qualified Prelude import qualified System.IO as IO import Prelude hiding (map, mapM, mapM_, filter, drop, dropWhile, take, mconcat , sum, product, iterate, repeat, cycle, replicate, splitAt , takeWhile, enumFrom, enumFromTo, enumFromThen, length , print, zipWith, zip, zipWith3, zip3, unzip, seq, show, read , readLn, sequence, concat, span, break, readFile, writeFile , minimum, maximum, elem, notElem, all, any, head , last, foldMap) -- $setup -- >>> import Control.Applicative -- >>> import qualified Control.Foldl as L -- >>> import Data.Bifunctor (first) -- >>> import Data.Function ((&)) -- >>> import Data.IORef -- >>> import Data.Vector (Vector) -- >>> import qualified Streaming.Prelude as S -- >>> import qualified System.IO -- >>> import Text.Read (readEither) -- instance (Eq a) => Eq1 (Of a) where eq1 = (==) -- instance (Ord a) => Ord1 (Of a) where compare1 = compare -- instance (Read a) => Read1 (Of a) where readsPrec1 = readsPrec -- instance (Show a) => Show1 (Of a) where showsPrec1 = showsPrec {-| Note that 'lazily', 'strictly', 'fst'', and 'mapOf' are all so-called /natural transformations/ on the primitive @Of a@ functor. If we write > type f ~~> g = forall x . f x -> g x then we can restate some types as follows: > mapOf :: (a -> b) -> Of a ~~> Of b -- Bifunctor first > lazily :: Of a ~~> (,) a > Identity . fst' :: Of a ~~> Identity a Manipulation of a @Stream f m r@ by mapping often turns on recognizing natural transformations of @f@. Thus @maps@ is far more general the the @map@ of the @Streaming.Prelude@, which can be defined thus: > S.map :: (a -> b) -> Stream (Of a) m r -> Stream (Of b) m r > S.map f = maps (mapOf f) i.e. > S.map f = maps (\(a :> x) -> (f a :> x)) This rests on recognizing that @mapOf@ is a natural transformation; note though that it results in such a transformation as well: > S.map :: (a -> b) -> Stream (Of a) m ~~> Stream (Of b) m Thus we can @maps@ it in turn. -} lazily :: Of a b -> (a,b) lazily = \(a:>b) -> (a,b) {-# INLINE lazily #-} {-| Convert a standard Haskell pair into a left-strict pair -} strictly :: (a,b) -> Of a b strictly = \(a,b) -> a :> b {-# INLINE strictly #-} {-| @fst'@ and @snd'@ extract the first and second element of a pair >>> S.fst' (1:>"hi") 1 >>> S.snd' (1:>"hi") "hi" They are contained in the @_first@ and @_second@ lenses, if any lens library is in scope >>> import Lens.Micro >>> (1:>"hi") ^. S._first 1 >>> (1:>"hi") ^. S._second "hi" -} fst' :: Of a b -> a fst' (a :> _) = a {-# INLINE fst' #-} snd' :: Of a b -> b snd' (_ :> b) = b {-# INLINE snd' #-} {-| Map a function over the first element of an @Of@ pair >>> S.mapOf even (1:>"hi") False :> "hi" @mapOf@ is just @first@ from the @Bifunctor@ instance >>> first even (1:>"hi") False :> "hi" and is contained in the @_first@ lens >>> import Lens.Micro >>> over S._first even (1:>"hi") False :> "hi" -} mapOf :: (a -> b) -> Of a r -> Of b r mapOf f (a :> b) = f a :> b {-# INLINE mapOf #-} {-| A lens into the first element of a left-strict pair -} _first :: Functor f => (a -> f a') -> Of a b -> f (Of a' b) _first afb (a :> b) = fmap (\c -> c :> b) (afb a) {-# INLINE _first #-} {-| A lens into the second element of a left-strict pair -} _second :: Functor f => (b -> f b') -> Of a b -> f (Of a b') _second afb (a :> b) = fmap (\c -> a :> c) (afb b) {-# INLINABLE _second #-} all :: Monad m => (a -> Bool) -> Stream (Of a) m r -> m (Of Bool r) all thus = loop True where loop b str = case str of Return r -> return (b :> r) Effect m -> m >>= loop b Step (a :> rest) -> if thus a then loop True rest else do r <- effects rest return (False :> r) {-# INLINABLE all #-} all_ :: Monad m => (a -> Bool) -> Stream (Of a) m r -> m Bool all_ thus = loop True where loop b str = case str of Return _ -> return b Effect m -> m >>= loop b Step (a :> rest) -> if thus a then loop True rest else return False {-# INLINABLE all_ #-} any :: Monad m => (a -> Bool) -> Stream (Of a) m r -> m (Of Bool r) any thus = loop False where loop b str = case str of Return r -> return (b :> r) Effect m -> m >>= loop b Step (a :> rest) -> if thus a then do r <- effects rest return (True :> r) else loop False rest {-# INLINABLE any #-} any_ :: Monad m => (a -> Bool) -> Stream (Of a) m r -> m Bool any_ thus = loop False where loop b str = case str of Return _ -> return b Effect m -> m >>= loop b Step (a :> rest) -> if thus a then return True else loop False rest {-# INLINABLE any_ #-} {-| Break a sequence upon meeting element falls under a predicate, keeping it and the rest of the stream as the return value. >>> rest <- S.print $ S.break even $ each [1,1,2,3] 1 1 >>> S.print rest 2 3 -} break :: Monad m => (a -> Bool) -> Stream (Of a) m r -> Stream (Of a) m (Stream (Of a) m r) break thePred = loop where loop str = case str of Return r -> Return (Return r) Effect m -> Effect $ fmap loop m Step (a :> rest) -> if thePred a then Return (Step (a :> rest)) else Step (a :> loop rest) {-# INLINABLE break #-} {-| Yield elements, using a fold to maintain state, until the accumulated value satifies the supplied predicate. The fold will then be short-circuited and the element that breaks it will be put after the break. This function is easiest to use with 'Control.Foldl.purely' >>> rest <- each [1..10] & L.purely S.breakWhen L.sum (>10) & S.print 1 2 3 4 >>> S.print rest 5 6 7 8 9 10 -} breakWhen :: Monad m => (x -> a -> x) -> x -> (x -> b) -> (b -> Bool) -> Stream (Of a) m r -> Stream (Of a) m (Stream (Of a) m r) breakWhen step begin done thePred = loop0 begin where loop0 x stream = case stream of Return r -> return (return r) Effect mn -> Effect $ fmap (loop0 x) mn Step (a :> rest) -> loop a (step x a) rest loop a !x stream = if thePred (done x) then return (yield a >> stream) else case stream of Return r -> yield a >> return (return r) Effect mn -> Effect $ fmap (loop a x) mn Step (a' :> rest) -> do yield a loop a' (step x a') rest {-# INLINABLE breakWhen #-} {-| Break during periods where the predicate is not satisfied, grouping the periods when it is. >>> S.print $ mapped S.toList $ S.breaks not $ S.each [False,True,True,False,True,True,False] [True,True] [True,True] >>> S.print $ mapped S.toList $ S.breaks id $ S.each [False,True,True,False,True,True,False] [False] [False] [False] -} breaks :: Monad m => (a -> Bool) -> Stream (Of a) m r -> Stream (Stream (Of a) m) m r breaks thus = loop where loop stream = Effect $ do e <- next stream return $ case e of Left r -> Return r Right (a, p') -> if not (thus a) then Step $ fmap loop (yield a >> break thus p') else loop p' {-# INLINABLE breaks #-} {-| Apply an action to all values, re-yielding each. The return value (@y@) of the function is ignored. >>> S.product $ S.chain Prelude.print $ S.each [1..5] 1 2 3 4 5 120 :> () See also 'mapM' for a variant of this which uses the return value of the function to transorm the values in the stream. -} chain :: Monad m => (a -> m y) -> Stream (Of a) m r -> Stream (Of a) m r chain f = loop where loop str = case str of Return r -> return r Effect mn -> Effect (fmap loop mn) Step (a :> rest) -> Effect $ do _ <- f a return (Step (a :> loop rest)) {-# INLINABLE chain #-} {-| Make a stream of foldable containers into a stream of their separate elements. This is just > concat str = for str each >>> S.print $ S.concat (each ["xy","z"]) 'x' 'y' 'z' Note that it also has the effect of 'Data.Maybe.catMaybes', 'Data.Either.rights' @map snd@ and such-like operations. >>> S.print $ S.concat $ S.each [Just 1, Nothing, Just 2] 1 2 >>> S.print $ S.concat $ S.each [Right 1, Left "Error!", Right 2] 1 2 >>> S.print $ S.concat $ S.each [('A',1), ('B',2)] 1 2 -} concat :: (Monad m, Foldable.Foldable f) => Stream (Of (f a)) m r -> Stream (Of a) m r concat = loop where loop str = case str of Return r -> Return r Effect m -> Effect (fmap loop m) Step (lst :> as) -> let inner [] = loop as inner (x:rest) = Step (x :> inner rest) in inner (Foldable.toList lst) {-# INLINABLE concat #-} -- The above hand-written loop is ~20% faster than the 'for' implementation -- concat str = for str each {-| The natural @cons@ for a @Stream (Of a)@. > cons a stream = yield a >> stream Useful for interoperation: > Data.Text.foldr S.cons (return ()) :: Text -> Stream (Of Char) m () > Lazy.foldrChunks S.cons (return ()) :: Lazy.ByteString -> Stream (Of Strict.ByteString) m () and so on. -} cons :: (Monad m) => a -> Stream (Of a) m r -> Stream (Of a) m r cons a str = Step (a :> str) {-# INLINE cons #-} {- | Cycle repeatedly through the layers of a stream, /ad inf./ This function is functor-general > cycle = forever >>> rest <- S.print $ S.splitAt 3 $ S.cycle (yield True >> yield False) True False True >>> S.print $ S.take 3 rest False True False -} cycle :: (Monad m, Functor f) => Stream f m r -> Stream f m s cycle str = loop where loop = str >> loop {-# INLINABLE cycle #-} {-| Interpolate a delay of n seconds between yields. -} delay :: MonadIO m => Double -> Stream (Of a) m r -> Stream (Of a) m r delay seconds = loop where pico = truncate (seconds * 1000000) loop str = do e <- lift $ next str case e of Left r -> Return r Right (a,rest) -> do yield a liftIO $ threadDelay pico loop rest {-# INLINABLE delay #-} {-| Where a transformer returns a stream, run the effects of the stream, keeping the return value. This is usually used at the type > drained :: Monad m => Stream (Of a) m (Stream (Of b) m r) -> Stream (Of a) m r > drained = join . fmap (lift . effects) Here, for example, we split a stream in two places and throw out the middle segment: >>> rest <- S.print $ S.drained $ S.splitAt 2 $ S.splitAt 5 $ each [1..7] 1 2 >>> S.print rest 6 7 In particular, we can define versions of @take@ and @takeWhile@ which retrieve the return value of the rest of the stream - and which can thus be used with 'maps': > take' n = S.drained . S.splitAt n > takeWhile' thus = S.drained . S.span thus -} drained :: (Monad m, Monad (t m), MonadTrans t) => t m (Stream (Of a) m r) -> t m r drained tms = tms >>= lift . effects {-# INLINE drained #-} -- --------------- -- drop -- --------------- {-| Ignore the first n elements of a stream, but carry out the actions >>> S.toList $ S.drop 2 $ S.replicateM 5 getLine a b c d e ["c","d","e"] :> () Because it retains the final return value, @drop n@ is a suitable argument for @maps@: >>> S.toList $ concats $ maps (S.drop 4) $ chunksOf 5 $ each [1..20] [5,10,15,20] :> () -} drop :: (Monad m) => Int -> Stream (Of a) m r -> Stream (Of a) m r drop n str | n <= 0 = str drop n str = loop n str where loop 0 stream = stream loop m stream = case stream of Return r -> Return r Effect ma -> Effect (fmap (loop m) ma) Step (_ :> as) -> loop (m-1) as {-# INLINABLE drop #-} -- --------------- -- dropWhile -- --------------- {- | Ignore elements of a stream until a test succeeds, retaining the rest. >>> S.print $ S.dropWhile ((< 5) . length) S.stdinLn one two three "three" four "four" ^CInterrupted. -} dropWhile :: Monad m => (a -> Bool) -> Stream (Of a) m r -> Stream (Of a) m r dropWhile thePred = loop where loop stream = case stream of Return r -> Return r Effect ma -> Effect (fmap loop ma) Step (a :> as) -> if thePred a then loop as else Step (a :> as) {-# INLINABLE dropWhile #-} -- --------------- -- each -- --------------- {- | Stream the elements of a pure, foldable container. >>> S.print $ each [1..3] 1 2 3 -} each :: (Monad m, Foldable.Foldable f) => f a -> Stream (Of a) m () each = Foldable.foldr (\a p -> Step (a :> p)) (Return ()) {-# INLINABLE each #-} -- --------------- -- effects -- --------------- {- | Reduce a stream, performing its actions but ignoring its elements. >>> rest <- S.effects $ S.splitAt 2 $ each [1..5] >>> S.print rest 3 4 5 'effects' should be understood together with 'copy' and is subject to the rules > S.effects . S.copy = id > hoist S.effects . S.copy = id The similar @effects@ and @copy@ operations in @Data.ByteString.Streaming@ obey the same rules. -} effects :: Monad m => Stream (Of a) m r -> m r effects = loop where loop stream = case stream of Return r -> return r Effect m -> m >>= loop Step (_ :> rest) -> loop rest {-# INLINABLE effects #-} {-| Before evaluating the monadic action returning the next step in the 'Stream', @wrapEffect@ extracts the value in a monadic computation @m a@ and passes it to a computation @a -> m y@. -} wrapEffect :: (Monad m, Functor f) => m a -> (a -> m y) -> Stream f m r -> Stream f m r wrapEffect m f = loop where loop stream = do x <- lift m step <- lift $ inspect stream _ <- lift $ f x either pure loop' step loop' stream = wrap (fmap loop stream) {-| Exhaust a stream remembering only whether @a@ was an element. -} elem :: (Monad m, Eq a) => a -> Stream (Of a) m r -> m (Of Bool r) elem a' = loop False where loop True str = fmap (True :>) (effects str) loop False str = case str of Return r -> return (False :> r) Effect m -> m >>= loop False Step (a:> rest) -> if a == a' then fmap (True :>) (effects rest) else loop False rest {-# INLINABLE elem #-} elem_ :: (Monad m, Eq a) => a -> Stream (Of a) m r -> m Bool elem_ a' = loop False where loop True _ = return True loop False str = case str of Return _ -> return False Effect m -> m >>= loop False Step (a:> rest) -> if a == a' then return True else loop False rest {-# INLINABLE elem_ #-} -- ----- -- enumFrom -- ------ {-| An infinite stream of enumerable values, starting from a given value. It is the same as @S.iterate succ@. Because their return type is polymorphic, @enumFrom@, @enumFromThen@ and @iterate@ are useful for example with @zip@ and @zipWith@, which require the same return type in the zipped streams. With @each [1..]@ the following bit of connect-and-resume would be impossible: >>> rest <- S.print $ S.zip (S.enumFrom 'a') $ S.splitAt 3 $ S.enumFrom 1 ('a',1) ('b',2) ('c',3) >>> S.print $ S.take 3 rest 4 5 6 -} enumFrom :: (Monad m, Enum n) => n -> Stream (Of n) m r enumFrom = loop where loop !n = Effect (return (Step (n :> loop (succ n)))) {-# INLINABLE enumFrom #-} {-| An infinite sequence of enumerable values at a fixed distance, determined by the first and second values. See the discussion of 'Streaming.enumFrom' >>> S.print $ S.take 3 $ S.enumFromThen 100 200 100 200 300 -} enumFromThen:: (Monad m, Enum a) => a -> a -> Stream (Of a) m r enumFromThen first second = Streaming.Prelude.map toEnum (loop _first) where _first = fromEnum first _second = fromEnum second diff = _second - _first loop !s = Step (s :> loop (s+diff)) {-# INLINABLE enumFromThen #-} -- --------------- -- erase -- --------------- {- | Remove the elements from a stream of values, retaining the structure of layers. -} erase :: Monad m => Stream (Of a) m r -> Stream Identity m r erase = loop where loop str = case str of Return r -> Return r Effect m -> Effect (fmap loop m) Step (_:>rest) -> Step (Identity (loop rest)) {-# INLINABLE erase #-} -- --------------- -- filter -- --------------- -- | Skip elements of a stream that fail a predicate filter :: (Monad m) => (a -> Bool) -> Stream (Of a) m r -> Stream (Of a) m r filter thePred = loop where loop str = case str of Return r -> Return r Effect m -> Effect (fmap loop m) Step (a :> as) -> if thePred a then Step (a :> loop as) else loop as {-# INLINE filter #-} -- ~ 10% faster than INLINABLE in simple bench -- --------------- -- filterM -- --------------- -- | Skip elements of a stream that fail a monadic test filterM :: (Monad m) => (a -> m Bool) -> Stream (Of a) m r -> Stream (Of a) m r filterM thePred = loop where loop str = case str of Return r -> Return r Effect m -> Effect $ fmap loop m Step (a :> as) -> Effect $ do bool <- thePred a if bool then return $ Step (a :> loop as) else return $ loop as {-# INLINE filterM #-} -- ~ 10% faster than INLINABLE in simple bench -- -- --------------- -- -- first -- -- --------------- -- {- | Take either the first item in a stream or the return value, if it is empty. -- The typical mark of an infinite stream is a polymorphic return value; in -- that case, 'first' is a sort of @safeHead@ -- -- To iterate an action returning a 'Maybe', until it succeeds. -- -- -} -- first :: Monad m => Stream (Of r) m r -> m r -- first = loop where -- loop str = case str of -- Return r -> return r -- Effect m -> m >>= loop -- Step (r :> rest) -> return r -- {-# INLINABLE first #-} -- --------------- -- fold -- --------------- {- $folds Use these to fold the elements of a 'Stream'. >>> S.fold_ (+) 0 id $ S.each [1..10] 55 The general folds 'fold', 'fold_', 'foldM' and 'foldM_' are arranged for use with @Control.Foldl@ 'Control.Foldl.purely' and 'Control.Foldl.impurely' >>> L.purely fold_ L.sum $ each [1..10] 55 >>> L.purely fold_ (liftA3 (,,) L.sum L.product L.list) $ each [1..10] (55,3628800,[1,2,3,4,5,6,7,8,9,10]) All functions marked with an underscore (e.g. @fold_@, @sum_@) omit the stream's return value in a left-strict pair. They are good for exiting streaming completely, but when you are, e.g. @mapped@-ing over a @Stream (Stream (Of a) m) m r@, which is to be compared with @[[a]]@. Specializing, we have e.g. > mapped sum :: (Monad m, Num n) => Stream (Stream (Of Int)) IO () -> Stream (Of n) IO () > mapped (fold mappend mempty id) :: Stream (Stream (Of Int)) IO () -> Stream (Of Int) IO () >>> S.print $ mapped S.sum $ chunksOf 3 $ S.each [1..10] 6 15 24 10 >>> let three_folds = L.purely S.fold (liftA3 (,,) L.sum L.product L.list) >>> S.print $ mapped three_folds $ chunksOf 3 (each [1..10]) (6,6,[1,2,3]) (15,120,[4,5,6]) (24,504,[7,8,9]) (10,10,[10]) -} {-| Strict fold of a 'Stream' of elements, preserving only the result of the fold, not the return value of the stream. The third parameter will often be 'id' where a fold is written by hand: >>> S.fold_ (+) 0 id $ each [1..10] 55 It can be used to replace a standard Haskell type with one more suited to writing a strict accumulation function. It is also crucial to the Applicative instance for @Control.Foldl.Fold@ > Control.Foldl.purely fold :: Monad m => Fold a b -> Stream (Of a) m () -> m b -} fold_ :: Monad m => (x -> a -> x) -> x -> (x -> b) -> Stream (Of a) m r -> m b fold_ step begin done = fmap (\(a :> _) -> a) . fold step begin done {-# INLINE fold_ #-} {-| Strict fold of a 'Stream' of elements that preserves the return value. The third parameter will often be 'id' where a fold is written by hand: >>> S.fold (+) 0 id $ each [1..10] 55 :> () >>> S.fold (*) 1 id $ S.fold (+) 0 id $ S.copy $ each [1..10] 3628800 :> (55 :> ()) It can be used to replace a standard Haskell type with one more suited to writing a strict accumulation function. It is also crucial to the Applicative instance for @Control.Foldl.Fold@ We can apply such a fold @purely@ > Control.Foldl.purely S.fold :: Monad m => Fold a b -> Stream (Of a) m r -> m (Of b r) Thus, specializing a bit: > L.purely S.fold L.sum :: Stream (Of Int) Int r -> m (Of Int r) > mapped (L.purely S.fold L.sum) :: Stream (Stream (Of Int)) IO r -> Stream (Of Int) IO r Here we use the Applicative instance for @Control.Foldl.Fold@ to stream three-item segments of a stream together with their sums and products. >>> S.print $ mapped (L.purely S.fold (liftA3 (,,) L.list L.product L.sum)) $ chunksOf 3 $ each [1..10] ([1,2,3],6,6) ([4,5,6],120,15) ([7,8,9],504,24) ([10],10,10) -} fold :: Monad m => (x -> a -> x) -> x -> (x -> b) -> Stream (Of a) m r -> m (Of b r) fold step begin done str = fold_loop str begin where fold_loop stream !x = case stream of Return r -> return (done x :> r) Effect m -> m >>= \str' -> fold_loop str' x Step (a :> rest) -> fold_loop rest $! step x a {-# INLINE fold #-} {-| Strict, monadic fold of the elements of a @Stream (Of a)@ > Control.Foldl.impurely foldM :: Monad m => FoldM a b -> Stream (Of a) m () -> m b -} foldM_ :: Monad m => (x -> a -> m x) -> m x -> (x -> m b) -> Stream (Of a) m r -> m b foldM_ step begin done = fmap (\(a :> _) -> a) . foldM step begin done {-# INLINE foldM_ #-} {-| Strict, monadic fold of the elements of a @Stream (Of a)@ > Control.Foldl.impurely foldM' :: Monad m => FoldM a b -> Stream (Of a) m r -> m (b, r) Thus to accumulate the elements of a stream as a vector, together with a random element we might write: >>> L.impurely S.foldM (liftA2 (,) L.vectorM L.random) $ each [1..10::Int] :: IO (Of (Vector Int, Maybe Int) ()) ([1,2,3,4,5,6,7,8,9,10],Just 9) :> () -} foldM :: Monad m => (x -> a -> m x) -> m x -> (x -> m b) -> Stream (Of a) m r ->m (Of b r) foldM step begin done str = do x0 <- begin loop str x0 where loop stream !x = case stream of Return r -> done x >>= \b -> return (b :> r) Effect m -> m >>= \s -> loop s x Step (a :> rest) -> do x' <- step x a loop rest x' {-# INLINABLE foldM #-} -- the following requires GHC.Magic.oneShot: -- foldM step begin done str = do -- x <- begin -- (x' :> r) <- streamFold -- (\r x -> return (x :> r)) -- (\mx2mx -> oneShot (\x -> x `seq` mx2mx >>= ($ x) )) -- (\(a :> x2mx') -> oneShot (\x -> x `seq` (step x a >>= x2mx')) ) -- ( str) -- x -- b <- done x' -- return (b :> r) -- where seq = Prelude.seq -- {-# INLINE foldM #-} {-| A natural right fold for consuming a stream of elements. See also the more general 'iterTM' in the 'Streaming' module and the still more general 'destroy' > foldrT (\a p -> Streaming.yield a >> p) = id > foldrT (\a p -> Pipes.yield a >> p) :: Monad m => Stream (Of a) m r -> Producer a m r > foldrT (\a p -> Conduit.yield a >> p) :: Monad m => Stream (Of a) m r -> Conduit a m r -} foldrT :: (Monad m, MonadTrans t, Monad (t m)) => (a -> t m r -> t m r) -> Stream (Of a) m r -> t m r foldrT step = loop where loop stream = case stream of Return r -> return r Effect m -> lift m >>= loop Step (a :> as) -> step a (loop as) {-# INLINABLE foldrT #-} {-| A natural right fold for consuming a stream of elements. See also the more general 'iterT' in the 'Streaming' module and the still more general 'destroy' -} foldrM :: Monad m => (a -> m r -> m r) -> Stream (Of a) m r -> m r foldrM step = loop where loop stream = case stream of Return r -> return r Effect m -> m >>= loop Step (a :> as) -> step a (loop as) {-# INLINABLE foldrM #-} -- --------------- -- for -- --------------- -- | @for@ replaces each element of a stream with an associated stream. Note that the -- associated stream may layer any functor. for :: (Monad m, Functor f) => Stream (Of a) m r -> (a -> Stream f m x) -> Stream f m r for str0 f = loop str0 where loop str = case str of Return r -> Return r Effect m -> Effect $ fmap loop m Step (a :> as) -> f a *> loop as {-# INLINABLE for #-} -- -| Group layers of any functor by comparisons on a preliminary annotation -- groupedBy -- :: (Monad m, Functor f) => -- (a -> a -> Bool) -- -> Stream (Compose (Of a) f) m r -- -> Stream (Stream (Compose (Of a) f) m) m r -- groupedBy equals = loop where -- loop stream = Effect $ do -- e <- inspect stream -- return $ case e of -- Left r -> Return r -- Right s@(Compose (a :> p')) -> Step $ -- fmap loop (Step $ Compose (a :> fmap (span' (equals a)) p')) -- span' :: (Monad m, Functor f) => (a -> Bool) -> Stream (Compose (Of a) f) m r -- -> Stream (Compose (Of a) f) m (Stream (Compose (Of a) f) m r) -- span' thePred = loop where -- loop str = case str of -- Return r -> Return (Return r) -- Effect m -> Effect $ fmap loop m -- Step s@(Compose (a :> rest)) -> case thePred a of -- True -> Step (Compose (a :> fmap loop rest)) -- False -> Return (Step s) -- {-# INLINABLE groupedBy #-} {-| Group elements of a stream in accordance with the supplied comparison. >>> S.print $ mapped S.toList $ S.groupBy (>=) $ each [1,2,3,1,2,3,4,3,2,4,5,6,7,6,5] [1] [2] [3,1,2,3] [4,3,2,4] [5] [6] [7,6,5] -} groupBy :: Monad m => (a -> a -> Bool) -> Stream (Of a) m r -> Stream (Stream (Of a) m) m r groupBy equals = loop where loop stream = Effect $ do e <- next stream return $ case e of Left r -> Return r Right (a, p') -> Step $ fmap loop (yield a >> span (equals a) p') {-# INLINABLE groupBy #-} {-| Group successive equal items together >>> S.toList $ mapped S.toList $ S.group $ each "baaaaad" ["b","aaaaa","d"] :> () >>> S.toList $ concats $ maps (S.drained . S.splitAt 1) $ S.group $ each "baaaaaaad" "bad" :> () -} group :: (Monad m, Eq a) => Stream (Of a) m r -> Stream (Stream (Of a) m) m r group = groupBy (==) {-# INLINE group #-} head :: Monad m => Stream (Of a) m r -> m (Of (Maybe a) r) head str = case str of Return r -> return (Nothing :> r) Effect m -> m >>= head Step (a :> rest) -> effects rest >>= \r -> return (Just a :> r) {-# INLINABLE head #-} head_ :: Monad m => Stream (Of a) m r -> m (Maybe a) head_ str = case str of Return _ -> return Nothing Effect m -> m >>= head_ Step (a :> _) -> return (Just a) {-# INLINABLE head_ #-} {-| Intersperse given value between each element of the stream. >>> S.print $ S.intersperse 0 $ each [1,2,3] 1 0 2 0 3 -} intersperse :: Monad m => a -> Stream (Of a) m r -> Stream (Of a) m r intersperse x str = case str of Return r -> Return r Effect m -> Effect (fmap (intersperse x) m) Step (a :> rest) -> loop a rest where loop !a theStr = case theStr of Return r -> Step (a :> Return r) Effect m -> Effect (fmap (loop a) m) Step (b :> rest) -> Step (a :> Step (x :> loop b rest)) {-# INLINABLE intersperse #-} -- --------------- -- iterate -- --------------- {-| Iterate a pure function from a seed value, streaming the results forever -} iterate :: Monad m => (a -> a) -> a -> Stream (Of a) m r iterate f = loop where loop a' = Effect (return (Step (a' :> loop (f a')))) {-# INLINABLE iterate #-} -- | Iterate a monadic function from a seed value, streaming the results forever iterateM :: Monad m => (a -> m a) -> m a -> Stream (Of a) m r iterateM f = loop where loop ma = Effect $ do a <- ma return (Step (a :> loop (f a))) {-# INLINABLE iterateM #-} last :: Monad m => Stream (Of a) m r -> m (Of (Maybe a) r) last = loop Nothing_ where loop mb str = case str of Return r -> case mb of Nothing_ -> return (Nothing :> r) Just_ a -> return (Just a :> r) Effect m -> m >>= loop mb Step (a :> rest) -> loop (Just_ a) rest {-# INLINABLE last #-} last_ :: Monad m => Stream (Of a) m r -> m (Maybe a) last_ = loop Nothing_ where loop mb str = case str of Return _ -> case mb of Nothing_ -> return Nothing Just_ a -> return (Just a) Effect m -> m >>= loop mb Step (a :> rest) -> loop (Just_ a) rest {-# INLINABLE last_ #-} -- --------------- -- length -- --------------- {-| Run a stream, remembering only its length: >>> runIdentity $ S.length_ (S.each [1..10] :: Stream (Of Int) Identity ()) 10 -} length_ :: Monad m => Stream (Of a) m r -> m Int length_ = fold_ (\n _ -> n + 1) 0 id {-# INLINE length_ #-} {-| Run a stream, keeping its length and its return value. >>> S.print $ mapped S.length $ chunksOf 3 $ S.each [1..10] 3 3 3 1 -} length :: Monad m => Stream (Of a) m r -> m (Of Int r) length = fold (\n _ -> n + 1) 0 id {-# INLINE length #-} -- --------------- -- map -- --------------- {-| Standard map on the elements of a stream. >>> S.stdoutLn $ S.map reverse $ each (words "alpha beta") ahpla ateb -} map :: Monad m => (a -> b) -> Stream (Of a) m r -> Stream (Of b) m r map f = maps (\(x :> rest) -> f x :> rest) -- loop where -- -- loop stream = case stream of -- Return r -> Return r -- Effect m -> Effect (fmap loop m) -- Step (a :> as) -> Step (f a :> loop as) {-# INLINABLE map #-} -- {-# NOINLINE [1] map #-} -- {-# RULES -- "map/map" [~1] forall f g bs . map f (map g bs) = -- map (f . g) bs -- #-} {-| Replace each element of a stream with the result of a monadic action >>> S.print $ S.mapM readIORef $ S.chain (\ior -> modifyIORef ior (*100)) $ S.mapM newIORef $ each [1..6] 100 200 300 400 500 600 See also 'chain' for a variant of this which ignores the return value of the function and just uses the side effects. -} mapM :: Monad m => (a -> m b) -> Stream (Of a) m r -> Stream (Of b) m r mapM f = loop where loop str = case str of Return r -> Return r Effect m -> Effect (fmap loop m) Step (a :> as) -> Effect $ do a' <- f a return (Step (a' :> loop as) ) {-# INLINABLE mapM #-} {-| Reduce a stream to its return value with a monadic action. >>> S.mapM_ Prelude.print $ each [1..3] 1 2 3 >>> rest <- S.mapM_ Prelude.print $ S.splitAt 3 $ each [1..10] 1 2 3 >>> S.sum rest 49 :> () -} mapM_ :: Monad m => (a -> m x) -> Stream (Of a) m r -> m r mapM_ f = loop where loop str = case str of Return r -> return r Effect m -> m >>= loop Step (a :> as) -> f a *> loop as {-# INLINABLE mapM_ #-} {- | Map layers of one functor to another with a transformation involving the base monad. This could be trivial, e.g. > let noteBeginning text x = putStrLn text >> return text this is completely functor-general @maps@ and @mapped@ obey these rules: > maps id = id > mapped return = id > maps f . maps g = maps (f . g) > mapped f . mapped g = mapped (f <=< g) > maps f . mapped g = mapped (fmap f . g) > mapped f . maps g = mapped (f <=< fmap g) @maps@ is more fundamental than @mapped@, which is best understood as a convenience for effecting this frequent composition: > mapped phi = decompose . maps (Compose . phi) -} mapped :: (Monad m, Functor f) => (forall x . f x -> m (g x)) -> Stream f m r -> Stream g m r mapped = mapsM {-# INLINE mapped #-} {-| A version of 'mapped' that imposes a 'Functor' constraint on the target functor rather than the source functor. This version should be preferred if 'fmap' on the target functor is cheaper. -} mappedPost :: (Monad m, Functor g) => (forall x . f x -> m (g x)) -> Stream f m r -> Stream g m r mappedPost = mapsMPost {-# INLINE mappedPost #-} {-| Map each element of the stream to a monoid, and take the monoidal sum of the results. >>> S.foldMap Sum $ S.take 2 (S.stdinLn) 1 2 3 Sum {getSum = 6} :> () -} foldMap :: (Monad m, Monoid w) => (a -> w) -> Stream (Of a) m r -> m (Of w r) foldMap f = fold (\ !acc a -> mappend acc (f a)) mempty id {-# INLINE foldMap #-} foldMap_ :: (Monad m, Monoid w) => (a -> w) -> Stream (Of a) m r -> m w foldMap_ f = fold_ (\ !acc a -> mappend acc (f a)) mempty id {-# INLINE foldMap_ #-} {-| Fold streamed items into their monoidal sum >>> S.mconcat $ S.take 2 $ S.map (Data.Monoid.Last . Just) S.stdinLn first last Last {getLast = Just "last"} :> () -} mconcat :: (Monad m, Monoid w) => Stream (Of w) m r -> m (Of w r) mconcat = fold mappend mempty id {-# INLINE mconcat #-} data Maybe_ a = Just_ !a | Nothing_ mconcat_ :: (Monad m, Monoid w) => Stream (Of w) m r -> m w mconcat_ = fold_ mappend mempty id minimum :: (Monad m, Ord a) => Stream (Of a) m r -> m (Of (Maybe a) r) minimum = fold (\m a -> case m of Nothing_ -> Just_ a ; Just_ a' -> Just_ (min a a')) Nothing_ (\m -> case m of Nothing_ -> Nothing; Just_ r -> Just r) {-# INLINE minimum #-} minimum_ :: (Monad m, Ord a) => Stream (Of a) m r -> m (Maybe a) minimum_ = fold_ (\m a -> case m of Nothing_ -> Just_ a ; Just_ a' -> Just_ (min a a')) Nothing_ (\m -> case m of Nothing_ -> Nothing; Just_ r -> Just r) {-# INLINE minimum_ #-} maximum :: (Monad m, Ord a) => Stream (Of a) m r -> m (Of (Maybe a) r) maximum = fold (\m a -> case m of Nothing_ -> Just_ a ; Just_ a' -> Just_ (max a a')) Nothing_ (\m -> case m of Nothing_ -> Nothing; Just_ r -> Just r) {-# INLINE maximum #-} maximum_ :: (Monad m, Ord a) => Stream (Of a) m r -> m (Maybe a) maximum_ = fold_ (\m a -> case m of Nothing_ -> Just_ a ; Just_ a' -> Just_ (max a a')) Nothing_ (\m -> case m of Nothing_ -> Nothing; Just_ r -> Just r) {-# INLINE maximum_ #-} {-| The standard way of inspecting the first item in a stream of elements, if the stream is still \'running\'. The @Right@ case contains a Haskell pair, where the more general @inspect@ would return a left-strict pair. There is no reason to prefer @inspect@ since, if the @Right@ case is exposed, the first element in the pair will have been evaluated to whnf. > next :: Monad m => Stream (Of a) m r -> m (Either r (a, Stream (Of a) m r)) > inspect :: Monad m => Stream (Of a) m r -> m (Either r (Of a (Stream (Of a) m r))) Interoperate with @pipes@ producers thus: > Pipes.unfoldr Stream.next :: Stream (Of a) m r -> Producer a m r > Stream.unfoldr Pipes.next :: Producer a m r -> Stream (Of a) m r Similarly: > IOStreams.unfoldM (fmap (either (const Nothing) Just) . next) :: Stream (Of a) IO b -> IO (InputStream a) > Conduit.unfoldM (fmap (either (const Nothing) Just) . next) :: Stream (Of a) m r -> Source a m r But see 'uncons', which is better fitted to these @unfoldM@s -} next :: Monad m => Stream (Of a) m r -> m (Either r (a, Stream (Of a) m r)) next = loop where loop stream = case stream of Return r -> return (Left r) Effect m -> m >>= loop Step (a :> rest) -> return (Right (a,rest)) {-# INLINABLE next #-} {-| Exhaust a stream deciding whether @a@ was an element. -} notElem :: (Monad m, Eq a) => a -> Stream (Of a) m r -> m (Of Bool r) notElem a' = loop True where loop False str = fmap (False :>) (effects str) loop True str = case str of Return r -> return (True:> r) Effect m -> m >>= loop True Step (a:> rest) -> if a == a' then fmap (False :>) (effects rest) else loop True rest {-# INLINABLE notElem #-} notElem_ :: (Monad m, Eq a) => a -> Stream (Of a) m r -> m Bool notElem_ a' = loop True where loop False _ = return False loop True str = case str of Return _ -> return True Effect m -> m >>= loop True Step (a:> rest) -> if a == a' then return False else loop True rest {-# INLINABLE notElem_ #-} {-| Remove repeated elements from a Stream. 'nubOrd' of course accumulates a 'Data.Set.Set' of elements that have already been seen and should thus be used with care. >>> S.toList_ $ S.nubOrd $ S.take 5 S.readLn :: IO [Int] 1 2 3 1 2 [1,2,3] -} nubOrd :: (Monad m, Ord a) => Stream (Of a) m r -> Stream (Of a) m r nubOrd = nubOrdOn id {-# INLINE nubOrd #-} {-| Use 'nubOrdOn' to have a custom ordering function for your elements. -} nubOrdOn :: (Monad m, Ord b) => (a -> b) -> Stream (Of a) m r -> Stream (Of a) m r nubOrdOn f xs = loop mempty xs where loop !set stream = case stream of Return r -> Return r Effect m -> Effect (liftM (loop set) m) Step (a :> rest) -> let !fa = f a in if Set.member fa set then loop set rest else Step (a :> loop (Set.insert fa set) rest) {-| More efficient versions of above when working with 'Int's that use 'Data.IntSet.IntSet'. -} nubInt :: Monad m => Stream (Of Int) m r -> Stream (Of Int) m r nubInt = nubIntOn id {-# INLINE nubInt #-} nubIntOn :: Monad m => (a -> Int) -> Stream (Of a) m r -> Stream (Of a) m r nubIntOn f xs = loop mempty xs where loop !set stream = case stream of Return r -> Return r Effect m -> Effect (liftM (loop set) m) Step (a :> rest) -> let !fa = f a in if IntSet.member fa set then loop set rest else Step (a :> loop (IntSet.insert fa set) rest) {-| > filter p = hoist effects (partition p) -} partition :: Monad m => (a -> Bool) -> Stream (Of a) m r -> Stream (Of a) (Stream (Of a) m) r partition thus = loop where loop str = case str of Return r -> Return r Effect m -> Effect (fmap loop (lift m)) Step (a :> rest) -> if thus a then Step (a :> loop rest) else Effect $ do yield a return (loop rest) {-| Separate left and right values in distinct streams. ('separate' is a more powerful, functor-general, equivalent using 'Sum' in place of 'Either'). So, for example, to permit unlimited user input of @Int@s on condition of only two errors, we might write: >>> S.toList $ S.print $ S.take 2 $ partitionEithers $ S.map readEither $ S.stdinLn :: IO (Of [Int] ()) 1 2 qqqqqqqqqq "Prelude.read: no parse" 3 rrrrrrrrrr "Prelude.read: no parse" [1,2,3] :> () > partitionEithers = separate . maps S.eitherToSum > lefts = hoist S.effects . partitionEithers > rights = S.effects . partitionEithers > rights = S.concat -} partitionEithers :: Monad m => Stream (Of (Either a b)) m r -> Stream (Of a) (Stream (Of b) m) r partitionEithers = loop where loop str = case str of Return r -> Return r Effect m -> Effect (fmap loop (lift m)) Step (Left a :> rest) -> Step (a :> loop rest) Step (Right b :> rest) -> Effect $ do yield b return (loop rest) -- | Fold a 'Stream' of numbers into their product product_ :: (Monad m, Num a) => Stream (Of a) m () -> m a product_ = fold_ (*) 1 id {-# INLINE product_ #-} {-| Fold a 'Stream' of numbers into their product with the return value > mapped product :: Stream (Stream (Of Int)) m r -> Stream (Of Int) m r -} product :: (Monad m, Num a) => Stream (Of a) m r -> m (Of a r) product = fold (*) 1 id {-# INLINE product #-} -- --------------- -- read -- --------------- {- | Make a stream of strings into a stream of parsed values, skipping bad cases >>> S.sum_ $ S.read $ S.takeWhile (/= "total") S.stdinLn :: IO Int 1000 2000 total 3000 -} read :: (Monad m, Read a) => Stream (Of String) m r -> Stream (Of a) m r read stream = for stream $ \str -> case readMaybe str of Nothing -> return () Just r -> yield r {-# INLINE read #-} -- --------------- -- repeat -- --------------- {-| Repeat an element /ad inf./ . >>> S.print $ S.take 3 $ S.repeat 1 1 1 1 -} repeat :: Monad m => a -> Stream (Of a) m r repeat a = loop where loop = Effect (return (Step (a :> loop))) {-# INLINE repeat #-} {-| Repeat a monadic action /ad inf./, streaming its results. >>> S.toList $ S.take 2 $ repeatM getLine one two ["one","two"] -} repeatM :: Monad m => m a -> Stream (Of a) m r repeatM ma = loop where loop = do a <- lift ma yield a loop {-# INLINABLE repeatM #-} -- --------------- -- replicate -- --------------- -- | Repeat an element several times. replicate :: Monad m => Int -> a -> Stream (Of a) m () replicate n _ | n <= 0 = return () replicate n a = loop n where loop 0 = Return () loop m = Effect (return (Step (a :> loop (m-1)))) {-# INLINABLE replicate #-} {-| Repeat an action several times, streaming its results. >>> S.print $ S.replicateM 2 getCurrentTime 2015-08-18 00:57:36.124508 UTC 2015-08-18 00:57:36.124785 UTC -} replicateM :: Monad m => Int -> m a -> Stream (Of a) m () replicateM n _ | n <= 0 = return () replicateM n ma = loop n where loop 0 = Return () loop m = Effect $ do a <- ma return (Step (a :> loop (m-1))) {-# INLINABLE replicateM #-} {-| Read an @IORef (Maybe a)@ or a similar device until it reads @Nothing@. @reread@ provides convenient exit from the @io-streams@ library > reread readIORef :: IORef (Maybe a) -> Stream (Of a) IO () > reread Streams.read :: System.IO.Streams.InputStream a -> Stream (Of a) IO () -} reread :: Monad m => (s -> m (Maybe a)) -> s -> Stream (Of a) m () reread step s = loop where loop = Effect $ do m <- step s case m of Nothing -> return (Return ()) Just a -> return (Step (a :> loop)) {-# INLINABLE reread #-} {-| Strict left scan, streaming, e.g. successive partial results. The seed is yielded first, before any action of finding the next element is performed. >>> S.print $ S.scan (++) "" id $ each (words "a b c d") "" "a" "ab" "abc" "abcd" 'scan' is fitted for use with @Control.Foldl@, thus: >>> S.print $ L.purely S.scan L.list $ each [3..5] [] [3] [3,4] [3,4,5] -} scan :: Monad m => (x -> a -> x) -> x -> (x -> b) -> Stream (Of a) m r -> Stream (Of b) m r scan step begin done str = Step (done begin :> loop begin str) where loop !acc stream = case stream of Return r -> Return r Effect m -> Effect (fmap (loop acc) m) Step (a :> rest) -> let !acc' = step acc a in Step (done acc' :> loop acc' rest) {-# INLINABLE scan #-} {-| Strict left scan, accepting a monadic function. It can be used with 'FoldM's from @Control.Foldl@ using 'impurely'. Here we yield a succession of vectors each recording >>> let v = L.impurely scanM L.vectorM $ each [1..4::Int] :: Stream (Of (Vector Int)) IO () >>> S.print v [] [1] [1,2] [1,2,3] [1,2,3,4] -} scanM :: Monad m => (x -> a -> m x) -> m x -> (x -> m b) -> Stream (Of a) m r -> Stream (Of b) m r scanM step begin done str = Effect $ do x <- begin b <- done x return (Step (b :> loop x str)) where loop !x stream = case stream of -- note we have already yielded from x Return r -> Return r Effect m -> Effect (do stream' <- m return (loop x stream') ) Step (a :> rest) -> Effect (do x' <- step x a b <- done x' return (Step (b :> loop x' rest)) ) {-# INLINABLE scanM #-} {-| Label each element in a stream with a value accumulated according to a fold. >>> S.print $ S.scanned (*) 1 id $ S.each [100,200,300] (100,100) (200,20000) (300,6000000) >>> S.print $ L.purely S.scanned L.product $ S.each [100,200,300] (100,100) (200,20000) (300,6000000) -} scanned :: Monad m => (x -> a -> x) -> x -> (x -> b) -> Stream (Of a) m r -> Stream (Of (a,b)) m r scanned step begin done = loop Nothing' begin where loop !m !x stream = case stream of Return r -> return r Effect mn -> Effect $ fmap (loop m x) mn Step (a :> rest) -> case m of Nothing' -> do let !acc = step x a yield (a, done acc) loop (Just' a) acc rest Just' _ -> do let !acc = done (step x a) yield (a, acc) loop (Just' a) (step x a) rest {-# INLINABLE scanned #-} data Maybe' a = Just' a | Nothing' -- --------------- -- sequence -- --------------- {-| Like the 'Data.List.sequence' but streaming. The result type is a stream of a\'s, /but is not accumulated/; the effects of the elements of the original stream are interleaved in the resulting stream. Compare: > sequence :: Monad m => [m a] -> m [a] > sequence :: Monad m => Stream (Of (m a)) m r -> Stream (Of a) m r This obeys the rule -} sequence :: Monad m => Stream (Of (m a)) m r -> Stream (Of a) m r sequence = loop where loop stream = case stream of Return r -> Return r Effect m -> Effect $ fmap loop m Step (ma :> rest) -> Effect $ do a <- ma return (Step (a :> loop rest)) {-# INLINABLE sequence #-} -- --------------- -- show -- --------------- show :: (Monad m, Show a) => Stream (Of a) m r -> Stream (Of String) m r show = map Prelude.show {-# INLINE show #-} -- --------------- -- sum -- --------------- -- | Fold a 'Stream' of numbers into their sum sum_ :: (Monad m, Num a) => Stream (Of a) m () -> m a sum_ = fold_ (+) 0 id {-# INLINE sum_ #-} {-| Fold a 'Stream' of numbers into their sum with the return value > mapped S.sum :: Stream (Stream (Of Int)) m r -> Stream (Of Int) m r >>> S.sum $ each [1..10] 55 :> () >>> (n :> rest) <- S.sum $ S.splitAt 3 $ each [1..10] >>> System.IO.print n 6 >>> (m :> rest') <- S.sum $ S.splitAt 3 rest >>> System.IO.print m 15 >>> S.print rest' 7 8 9 10 -} sum :: (Monad m, Num a) => Stream (Of a) m r -> m (Of a r) sum = fold (+) 0 id {-# INLINABLE sum #-} -- --------------- -- span -- --------------- -- | Stream elements until one fails the condition, return the rest. span :: Monad m => (a -> Bool) -> Stream (Of a) m r -> Stream (Of a) m (Stream (Of a) m r) span thePred = loop where loop str = case str of Return r -> Return (Return r) Effect m -> Effect $ fmap loop m Step (a :> rest) -> if thePred a then Step (a :> loop rest) else Return (Step (a :> rest)) {-# INLINABLE span #-} {-| Split a stream of elements wherever a given element arises. The action is like that of 'Prelude.words'. >>> S.stdoutLn $ mapped S.toList $ S.split ' ' $ each "hello world " hello world -} split :: (Eq a, Monad m) => a -> Stream (Of a) m r -> Stream (Stream (Of a) m) m r split t = loop where loop stream = case stream of Return r -> Return r Effect m -> Effect (fmap loop m) Step (a :> rest) -> if a /= t then Step (fmap loop (yield a >> break (== t) rest)) else loop rest {-# INLINABLE split #-} {-| Split a succession of layers after some number, returning a streaming or effectful pair. This function is the same as the 'splitsAt' exported by the @Streaming@ module, but since this module is imported qualified, it can usurp a Prelude name. It specializes to: > splitAt :: (Monad m, Functor f) => Int -> Stream (Of a) m r -> Stream (Of a) m (Stream (Of a) m r) -} splitAt :: (Monad m, Functor f) => Int -> Stream f m r -> Stream f m (Stream f m r) splitAt = splitsAt {-# INLINE splitAt #-} -- ------- -- subst -- ------- {-| Replace each element in a stream of individual values with a functorial layer of any sort. @subst = flip with@ and is more convenient in a sequence of compositions that transform a stream. > with = flip subst > for str f = concats $ subst f str > subst f = maps (\(a:>r) -> r <$ f a) > S.concat = concats . subst each -} subst :: (Monad m, Functor f) => (a -> f x) -> Stream (Of a) m r -> Stream f m r subst f s = loop s where loop str = case str of Return r -> Return r Effect m -> Effect (fmap loop m) Step (a :> rest) -> Step (loop rest <$ f a) {-# INLINABLE subst #-} -- --------------- -- take -- --------------- {-| End a stream after n elements; the original return value is thus lost. 'splitAt' preserves this information. Note that, like @splitAt@, this function is functor-general, so that, for example, you can @take@ not just a number of items from a stream of elements, but a number of substreams and the like. >>> S.toList $ S.take 3 $ each "with" "wit" :> () >>> S.readFile "stream.hs" (S.stdoutLn . S.take 3) import Streaming import qualified Streaming.Prelude as S import Streaming.Prelude (each, next, yield) -} take :: (Monad m, Functor f) => Int -> Stream f m r -> Stream f m () take n0 _ | n0 <= 0 = return () take n0 str = loop n0 str where loop 0 _ = return () loop n p = case p of Step fas -> Step (fmap (loop (n-1)) fas) Effect m -> Effect (fmap (loop n) m) Return _ -> Return () {-# INLINABLE take #-} -- --------------- -- takeWhile -- --------------- {-| End stream when an element fails a condition; the original return value is lost. By contrast 'span' preserves this information, and is generally more desirable. > S.takeWhile thus = void . S.span thus To preserve the information - but thus also force the rest of the stream to be developed - write > S.drained . S.span thus as @dropWhile thus@ is > S.effects . S.span thus -} takeWhile :: Monad m => (a -> Bool) -> Stream (Of a) m r -> Stream (Of a) m () takeWhile thePred = loop where loop str = case str of Step (a :> as) -> when (thePred a) (Step (a :> loop as)) Effect m -> Effect (fmap loop m) Return _ -> Return () {-# INLINE takeWhile #-} {-| Like 'takeWhile', but takes a monadic predicate. -} takeWhileM :: Monad m => (a -> m Bool) -> Stream (Of a) m r -> Stream (Of a) m () takeWhileM thePred = loop where loop str = case str of Step (a :> as) -> do b <- lift (thePred a) when b (Step (a :> loop as)) Effect m -> Effect (fmap loop m) Return _ -> Return () {-# INLINE takeWhileM #-} {-| Convert an effectful @Stream (Of a)@ into a list of @as@ Note: Needless to say, this function does not stream properly. It is basically the same as Prelude 'mapM' which, like 'replicateM', 'sequence' and similar operations on traversable containers is a leading cause of space leaks. -} toList_ :: Monad m => Stream (Of a) m r -> m [a] toList_ = fold_ (\diff a ls -> diff (a: ls)) id (\diff -> diff []) {-# INLINE toList_ #-} {-| Convert an effectful 'Stream' into a list alongside the return value > mapped toList :: Stream (Stream (Of a) m) m r -> Stream (Of [a]) m r Like 'toList_', 'toList' breaks streaming; unlike 'toList_' it /preserves the return value/ and thus is frequently useful with e.g. 'mapped' >>> S.print $ mapped S.toList $ chunksOf 3 $ each [1..9] [1,2,3] [4,5,6] [7,8,9] >>> S.print $ mapped S.toList $ chunksOf 2 $ S.replicateM 4 getLine s t ["s","t"] u v ["u","v"] -} toList :: Monad m => Stream (Of a) m r -> m (Of [a] r) toList = fold (\diff a ls -> diff (a: ls)) id (\diff -> diff []) {-# INLINE toList #-} {-| Inspect the first item in a stream of elements, without a return value. @uncons@ provides convenient exit into another streaming type: > IOStreams.unfoldM uncons :: Stream (Of a) IO b -> IO (InputStream a) > Conduit.unfoldM uncons :: Stream (Of a) m r -> Conduit.Source m a -} uncons :: Monad m => Stream (Of a) m r -> m (Maybe (a, Stream (Of a) m r)) uncons = loop where loop stream = case stream of Return _ -> return Nothing Effect m -> m >>= loop Step (a :> rest) -> return (Just (a,rest)) {-# INLINABLE uncons #-} {-| Build a @Stream@ by unfolding steps starting from a seed. In particular note that @S.unfoldr S.next = id@. The seed can of course be anything, but this is one natural way to consume a @pipes@ 'Pipes.Producer'. Consider: >>> S.stdoutLn $ S.take 2 $ S.unfoldr Pipes.next Pipes.stdinLn hello hello goodbye goodbye >>> S.stdoutLn $ S.unfoldr Pipes.next (Pipes.stdinLn >-> Pipes.take 2) hello hello goodbye goodbye >>> S.effects $ S.unfoldr Pipes.next (Pipes.stdinLn >-> Pipes.take 2 >-> Pipes.stdoutLn) hello hello goodbye goodbye @Pipes.unfoldr S.next@ similarly unfolds a @Pipes.Producer@ from a stream. -} unfoldr :: Monad m => (s -> m (Either r (a, s))) -> s -> Stream (Of a) m r unfoldr step = loop where loop s0 = Effect (do e <- step s0 case e of Left r -> return (Return r) Right (a,s) -> return (Step (a :> loop s))) {-# INLINABLE unfoldr #-} -- --------------------------------------- -- untilLeft -- --------------------------------------- untilLeft :: Monad m => m (Either r a) -> Stream (Of a) m r untilLeft act = Effect loop where loop = do e <- act case e of Right a -> return (Step (a :> Effect loop)) Left r -> return (Return r) {-# INLINABLE untilLeft #-} -- --------------------------------------- -- untilRight -- --------------------------------------- untilRight :: Monad m => m (Either a r) -> Stream (Of a) m r untilRight act = Effect loop where loop = do e <- act case e of Right r -> return (Return r) Left a -> return (Step (a :> Effect loop)) {-# INLINABLE untilRight #-} -- --------------------------------------- -- with -- --------------------------------------- {-| Replace each element in a stream of individual Haskell values (a @Stream (Of a) m r@) with an associated 'functorial' step. > for str f = concats (with str f) > with str f = for str (yields . f) > with str f = maps (\(a:>r) -> r <$ f a) str > with = flip subst > subst = flip with >>> with (each [1..3]) (yield . Prelude.show) & intercalates (yield "--") & S.stdoutLn 1 -- 2 -- 3 -} with :: (Monad m, Functor f) => Stream (Of a) m r -> (a -> f x) -> Stream f m r with s f = loop s where loop str = case str of Return r -> Return r Effect m -> Effect (fmap loop m) Step (a :> rest) -> Step (loop rest <$ f a) {-# INLINABLE with #-} -- --------------------------------------- -- yield -- --------------------------------------- {-| A singleton stream >>> stdoutLn $ yield "hello" hello >>> S.sum $ do {yield 1; yield 2; yield 3} 6 :> () >>> let number = lift (putStrLn "Enter a number:") >> lift readLn >>= yield :: Stream (Of Int) IO () >>> S.toList $ do {number; number; number} Enter a number: 1 Enter a number: 2 Enter a number: 3 [1,2,3] :> () -} yield :: Monad m => a -> Stream (Of a) m () yield a = Step (a :> Return ()) {-# INLINE yield #-} -- | Zip two 'Stream's zip :: Monad m => Stream (Of a) m r -> Stream (Of b) m r -> Stream (Of (a,b)) m r zip = zipWith (,) {-# INLINE zip #-} -- | Zip two 'Stream's using the provided combining function zipWith :: Monad m => (a -> b -> c) -> Stream (Of a) m r -> Stream (Of b) m r -> Stream (Of c) m r zipWith f = loop where loop str0 str1 = case str0 of Return r -> Return r Effect m -> Effect $ fmap (\str -> loop str str1) m Step (a :> rest0) -> case str1 of Return r -> Return r Effect m -> Effect $ fmap (loop str0) m Step (b :> rest1) -> Step (f a b :>loop rest0 rest1) {-# INLINABLE zipWith #-} -- | Zip three 'Stream's with a combining function zipWith3 :: Monad m => (a -> b -> c -> d) -> Stream (Of a) m r -> Stream (Of b) m r -> Stream (Of c) m r -> Stream (Of d) m r zipWith3 op = loop where loop str0 str1 str2 = do e0 <- lift (next str0) case e0 of Left r0 -> return r0 Right (a0,rest0) -> do e1 <- lift (next str1) case e1 of Left r1 -> return r1 Right (a1,rest1) -> do e2 <- lift (next str2) case e2 of Left r2 -> return r2 Right (a2,rest2) -> do yield (op a0 a1 a2) loop rest0 rest1 rest2 {-# INLINABLE zipWith3 #-} -- | Zip three 'Stream's together zip3 :: Monad m => Stream (Of a) m r -> Stream (Of b) m r -> Stream (Of c) m r -> Stream (Of (a,b,c)) m r zip3 = zipWith3 (,,) {-# INLINABLE zip3 #-} -- -------------- -- IO fripperies -- -------------- {-| View standard input as a @Stream (Of String) m r@. By contrast, 'stdoutLn' renders a @Stream (Of String) m r@ to standard output. The names follow @Pipes.Prelude@ >>> stdoutLn stdinLn hello hello world world ^CInterrupted. >>> stdoutLn $ S.map reverse stdinLn hello olleh world dlrow ^CInterrupted. -} stdinLn :: MonadIO m => Stream (Of String) m () stdinLn = fromHandle IO.stdin {-# INLINABLE stdinLn #-} {-| Read values from 'IO.stdin', ignoring failed parses. >>> :set -XTypeApplications >>> S.sum $ S.take 2 (S.readLn @IO @Int) 10 12 22 :> () >>> S.toList $ S.take 2 (S.readLn @IO @Int) 10 1@#$%^&*\ 12 [10,12] :> () -} readLn :: (MonadIO m, Read a) => Stream (Of a) m () readLn = loop where loop = do eof <- liftIO IO.isEOF unless eof $ do str <- liftIO getLine case readMaybe str of Nothing -> readLn Just n -> yield n >> loop {-# INLINABLE readLn #-} {-| Read 'String's from a 'IO.Handle' using 'IO.hGetLine' Terminates on end of input >>> IO.withFile "/usr/share/dict/words" IO.ReadMode $ S.stdoutLn . S.take 3 . S.drop 50000 . S.fromHandle deflagrator deflate deflation -} fromHandle :: MonadIO m => IO.Handle -> Stream (Of String) m () fromHandle h = go where go = do eof <- liftIO $ IO.hIsEOF h unless eof $ do str <- liftIO $ IO.hGetLine h yield str go {-# INLINABLE fromHandle #-} {-| Write a succession of strings to a handle as separate lines. >>> S.toHandle IO.stdout $ each (words "one two three") one two three -} toHandle :: MonadIO m => IO.Handle -> Stream (Of String) m r -> m r toHandle handle = loop where loop str = case str of Return r -> return r Effect m -> m >>= loop Step (s :> rest) -> do liftIO (IO.hPutStrLn handle s) loop rest {-# INLINABLE toHandle #-} {-| Print the elements of a stream as they arise. >>> S.print $ S.take 2 S.stdinLn hello "hello" world "world" -} print :: (MonadIO m, Show a) => Stream (Of a) m r -> m r print = loop where loop stream = case stream of Return r -> return r Effect m -> m >>= loop Step (a :> rest) -> do liftIO (Prelude.print a) loop rest {-| Write 'String's to 'IO.stdout' using 'putStrLn'; terminates on a broken output pipe (The name and implementation are modelled on the @Pipes.Prelude@ @stdoutLn@). >>> S.stdoutLn $ S.take 3 $ S.each $ words "one two three four five" one two three -} stdoutLn :: MonadIO m => Stream (Of String) m () -> m () stdoutLn = loop where loop stream = case stream of Return _ -> return () Effect m -> m >>= loop Step (s :> rest) -> do x <- liftIO $ try (putStrLn s) case x of Left (G.IOError { G.ioe_type = G.ResourceVanished , G.ioe_errno = Just ioe }) | Errno ioe == ePIPE -> return () Left e -> liftIO (throwIO e) Right () -> loop rest {-# INLINABLE stdoutLn #-} {-| Read the lines of a file, using a function of the type: \'@'Stream' ('Of' 'String') 'IO' () -> 'IO' a@\' to turn the stream into a value of type \''IO' a\'. >>> S.writeFile "lines.txt" $ S.take 2 S.stdinLn hello world >>> S.readFile "lines.txt" S.print "hello" "world" -} readFile :: FilePath -> (Stream (Of String) IO () -> IO a) -> IO a readFile f s = IO.withFile f IO.ReadMode $ \h -> s (fromHandle h) {-| Write a series of 'String's as lines to a file. >>> S.writeFile "lines.txt" $ S.take 2 S.stdinLn hello world >>> S.readFile "lines.txt" S.stdoutLn hello world -} writeFile :: FilePath -> Stream (Of String) IO r -> IO r writeFile f = IO.withFile f IO.WriteMode . flip toHandle {-| Write 'String's to 'IO.stdout' using 'putStrLn' Unlike @stdoutLn@, @stdoutLn'@ does not handle a broken output pipe. Thus it can have a polymorphic return value, rather than @()@, and this kind of \"connect and resume\" is possible: >>> rest <- S.stdoutLn' $ S.show $ S.splitAt 3 (each [1..5]) 1 2 3 >>> S.toList rest [4,5] :> () -} stdoutLn' :: MonadIO m => Stream (Of String) m r -> m r stdoutLn' = toHandle IO.stdout distinguish :: (a -> Bool) -> Of a r -> Sum (Of a) (Of a) r distinguish predicate (a :> b) = if predicate a then InR (a :> b) else InL (a :> b) {-# INLINE distinguish #-} sumToEither ::Sum (Of a) (Of b) r -> Of (Either a b) r sumToEither s = case s of InL (a :> r) -> Left a :> r InR (b :> r) -> Right b :> r {-# INLINE sumToEither #-} eitherToSum :: Of (Either a b) r -> Sum (Of a) (Of b) r eitherToSum s = case s of Left a :> r -> InL (a :> r) Right b :> r -> InR (b :> r) {-# INLINE eitherToSum #-} composeToSum :: Compose (Of Bool) f r -> Sum f f r composeToSum x = case x of Compose (True :> f) -> InR f Compose (False :> f) -> InL f {-# INLINE composeToSum #-} sumToCompose :: Sum f f r -> Compose (Of Bool) f r sumToCompose x = case x of InR f -> Compose (True :> f) InL f -> Compose (False :> f) {-# INLINE sumToCompose #-} {-| Store the result of any suitable fold over a stream, keeping the stream for further manipulation. @store f = f . copy@ : >>> S.print $ S.store S.product $ each [1..4] 1 2 3 4 24 :> () >>> S.print $ S.store S.sum $ S.store S.product $ each [1..4] 1 2 3 4 10 :> (24 :> ()) Here the sum (10) and the product (24) have been \'stored\' for use when finally we have traversed the stream with 'print' . Needless to say, a second 'pass' is excluded conceptually, so the folds that you apply successively with @store@ are performed simultaneously, and in constant memory -- as they would be if, say, you linked them together with @Control.Fold@: >>> L.impurely S.foldM (liftA3 (\a b c -> (b, c)) (L.sink Prelude.print) (L.generalize L.sum) (L.generalize L.product)) $ each [1..4] 1 2 3 4 (10,24) :> () Fusing folds after the fashion of @Control.Foldl@ will generally be a bit faster than the corresponding succession of uses of 'store', but by constant factor that will be completely dwarfed when any IO is at issue. But 'store' \/ 'copy' is /much/ more powerful, as you can see by reflecting on uses like this: >>> S.sum $ S.store (S.sum . mapped S.product . chunksOf 2) $ S.store (S.product . mapped S.sum . chunksOf 2) $ each [1..6] 21 :> (44 :> (231 :> ())) It will be clear that this cannot be reproduced with any combination of lenses, @Control.Fold@ folds, or the like. (See also the discussion of 'copy'.) It would conceivably be clearer to import a series of specializations of 'store'. It is intended to be used at types like these: > storeM :: (forall s m . Monad m => Stream (Of a) m s -> m (Of b s)) > -> (Monad n => Stream (Of a) n r -> Stream (Of a) n (Of b r)) > storeM = store > > storeMIO :: (forall s m . MonadIO m => Stream (Of a) m s -> m (Of b s)) > -> (MonadIO n => Stream (Of a) n r -> Stream (Of a) n (Of b r) > storeMIO = store It is clear from these types that we are just using the general instances: > instance (Functor f, Monad m) => Monad (Stream f m) > instance (Functor f, MonadIO m) => MonadIO (Stream f m) We thus can't be touching the elements of the stream, or the final return value. It is the same with other constraints that @Stream (Of a)@ inherits from the underlying monad, like 'MonadResource'. Thus I can independently filter and write to one file, but nub and write to another, or interact with a database and a logfile and the like: >>> (S.writeFile "hello2.txt" . S.nubOrd) $ store (S.writeFile "hello.txt" . S.filter (/= "world")) $ each ["hello", "world", "goodbye", "world"] >>> :! cat hello.txt hello goodbye >>> :! cat hello2.txt hello world goodbye -} store :: Monad m => (Stream (Of a) (Stream (Of a) m) r -> t) -> Stream (Of a) m r -> t store f x = f (copy x) {-# INLINE store #-} {-| Duplicate the content of stream, so that it can be acted on twice in different ways, but without breaking streaming. Thus, with @each [1,2]@ I might do: >>> S.print $ each ["one","two"] "one" "two" >>> S.stdoutLn $ each ["one","two"] one two With copy, I can do these simultaneously: >>> S.print $ S.stdoutLn $ S.copy $ each ["one","two"] "one" one "two" two 'copy' should be understood together with 'effects' and is subject to the rules > S.effects . S.copy = id > hoist S.effects . S.copy = id The similar operations in 'Data.ByteString.Streaming' obey the same rules. Where the actions you are contemplating are each simple folds over the elements, or a selection of elements, then the coupling of the folds is often more straightforwardly effected with `Control.Foldl`, e.g. >>> L.purely S.fold (liftA2 (,) L.sum L.product) $ each [1..10] (55,3628800) :> () rather than >>> S.sum $ S.product . S.copy $ each [1..10] 55 :> (3628800 :> ()) A @Control.Foldl@ fold can be altered to act on a selection of elements by using 'Control.Foldl.handles' on an appropriate lens. Some such manipulations are simpler and more 'Data.List'-like, using 'copy': >>> L.purely S.fold (liftA2 (,) (L.handles (L.filtered odd) L.sum) (L.handles (L.filtered even) L.product)) $ each [1..10] (25,3840) :> () becomes >>> S.sum $ S.filter odd $ S.product $ S.filter even $ S.copy $ each [1..10] 25 :> (3840 :> ()) or using 'store' >>> S.sum $ S.filter odd $ S.store (S.product . S.filter even) $ each [1..10] 25 :> (3840 :> ()) But anything that fold of a @Stream (Of a) m r@ into e.g. an @m (Of b r)@ that has a constraint on @m@ that is carried over into @Stream f m@ - e.g. @Monad@, @MonadIO@, @MonadResource@, etc. can be used on the stream. Thus, I can fold over different groupings of the original stream: >>> (S.toList . mapped S.toList . chunksOf 5) $ (S.toList . mapped S.toList . chunksOf 3) $ S.copy $ each [1..10] [[1,2,3,4,5],[6,7,8,9,10]] :> ([[1,2,3],[4,5,6],[7,8,9],[10]] :> ()) The procedure can be iterated as one pleases, as one can see from this (otherwise unadvisable!) example: >>> (S.toList . mapped S.toList . chunksOf 4) $ (S.toList . mapped S.toList . chunksOf 3) $ S.copy $ (S.toList . mapped S.toList . chunksOf 2) $ S.copy $ each [1..12] [[1,2,3,4],[5,6,7,8],[9,10,11,12]] :> ([[1,2,3],[4,5,6],[7,8,9],[10,11,12]] :> ([[1,2],[3,4],[5,6],[7,8],[9,10],[11,12]] :> ())) @copy@ can be considered a special case of 'expand': @ copy = 'expand' $ \p (a :> as) -> a :> p (a :> as) @ If 'Of' were an instance of 'Control.Comonad.Comonad', then one could write @ copy = 'expand' extend @ -} copy :: Monad m => Stream (Of a) m r -> Stream (Of a) (Stream (Of a) m) r copy = Effect . return . loop where loop str = case str of Return r -> Return r Effect m -> Effect (fmap loop (lift m)) Step (a :> rest) -> Effect (Step (a :> Return (Step (a :> loop rest)))) {-# INLINABLE copy#-} {-| An alias for @copy@. -} duplicate :: Monad m => Stream (Of a) m r -> Stream (Of a) (Stream (Of a) m) r duplicate = copy {-# INLINE duplicate #-} {-| The type > Data.List.unzip :: [(a,b)] -> ([a],[b]) might lead us to expect > Streaming.unzip :: Stream (Of (a,b)) m r -> Stream (Of a) m (Stream (Of b) m r) which would not stream, since it would have to accumulate the second stream (of @b@s). Of course, @Data.List@ 'Data.List.unzip' doesn't stream either. This @unzip@ does stream, though of course you can spoil this by using e.g. 'toList': >>> let xs = Prelude.map (\x -> (x, Prelude.show x)) [1..5 :: Int] >>> S.toList $ S.toList $ S.unzip (S.each xs) ["1","2","3","4","5"] :> ([1,2,3,4,5] :> ()) >>> Prelude.unzip xs ([1,2,3,4,5],["1","2","3","4","5"]) Note the difference of order in the results. It may be of some use to think why. The first application of 'toList' was applied to a stream of integers: >>> :t S.unzip $ S.each xs S.unzip $ S.each xs :: Monad m => Stream (Of Int) (Stream (Of String) m) () Like any fold, 'toList' takes no notice of the monad of effects. > toList :: Monad m => Stream (Of a) m r -> m (Of [a] r) In the case at hand (since I am in @ghci@) @m = Stream (Of String) IO@. So when I apply 'toList', I exhaust that stream of integers, folding it into a list: >>> :t S.toList $ S.unzip $ S.each xs S.toList $ S.unzip $ S.each xs :: Monad m => Stream (Of String) m (Of [Int] ()) When I apply 'toList' to /this/, I reduce everything to an ordinary action in @IO@, and return a list of strings: >>> S.toList $ S.toList $ S.unzip (S.each xs) ["1","2","3","4","5"] :> ([1,2,3,4,5] :> ()) 'unzip' can be considered a special case of either 'unzips' or 'expand': @ unzip = 'unzips' . 'maps' (\((a,b) :> x) -> Compose (a :> b :> x)) unzip = 'expand' $ \p ((a,b) :> abs) -> b :> p (a :> abs) @ -} unzip :: Monad m => Stream (Of (a,b)) m r -> Stream (Of a) (Stream (Of b) m) r unzip = loop where loop str = case str of Return r -> Return r Effect m -> Effect (fmap loop (lift m)) Step ((a,b):> rest) -> Step (a :> Effect (Step (b :> Return (loop rest)))) {-# INLINABLE unzip #-} {- $merging These functions combine two sorted streams of orderable elements into one sorted stream. The elements of the merged stream are guaranteed to be in a sorted order if the two input streams are also sorted. The merge operation is /left-biased/: when merging two elements that compare as equal, the left element is chosen first. -} {- | Merge two streams of elements ordered with their 'Ord' instance. The return values of both streams are returned. >>> S.print $ merge (each [1,3,5]) (each [2,4]) 1 2 3 4 5 ((), ()) -} merge :: (Monad m, Ord a) => Stream (Of a) m r -> Stream (Of a) m s -> Stream (Of a) m (r, s) merge = mergeBy compare {-# INLINE merge #-} {- | Merge two streams, ordering them by applying the given function to each element before comparing. The return values of both streams are returned. -} mergeOn :: (Monad m, Ord b) => (a -> b) -> Stream (Of a) m r -> Stream (Of a) m s -> Stream (Of a) m (r, s) mergeOn f = mergeBy (comparing f) {-# INLINE mergeOn #-} {- | Merge two streams, ordering the elements using the given comparison function. The return values of both streams are returned. -} mergeBy :: Monad m => (a -> a -> Ordering) -> Stream (Of a) m r -> Stream (Of a) m s -> Stream (Of a) m (r, s) mergeBy cmp = loop where loop str0 str1 = case str0 of Return r0 -> (\ r1 -> (r0, r1)) <$> str1 Effect m -> Effect $ fmap (\ str -> loop str str1) m Step (a :> rest0) -> case str1 of Return r1 -> (\ r0 -> (r0, r1)) <$> str0 Effect m -> Effect $ fmap (loop str0) m Step (b :> rest1) -> case cmp a b of LT -> Step (a :> loop rest0 str1) EQ -> Step (a :> loop rest0 str1) -- left-biased GT -> Step (b :> loop str0 rest1) {-# INLINABLE mergeBy #-} {- $maybes These functions discard the 'Nothing's that they encounter. They are analogous to the functions from @Data.Maybe@ that share their names. -} {-| The 'catMaybes' function takes a 'Stream' of 'Maybe's and returns a 'Stream' of all of the 'Just' values. 'concat' has the same behavior, but is more general; it works for any foldable container type. -} catMaybes :: Monad m => Stream (Of (Maybe a)) m r -> Stream (Of a) m r catMaybes = loop where loop stream = case stream of Return r -> Return r Effect m -> Effect (fmap loop m) Step (ma :> snext) -> case ma of Nothing -> loop snext Just a -> Step (a :> loop snext) {-# INLINABLE catMaybes #-} {-| The 'mapMaybe' function is a version of 'map' which can throw out elements. In particular, the functional argument returns something of type @'Maybe' b@. If this is 'Nothing', no element is added on to the result 'Stream'. If it is @'Just' b@, then @b@ is included in the result 'Stream'. -} mapMaybe :: Monad m => (a -> Maybe b) -> Stream (Of a) m r -> Stream (Of b) m r mapMaybe phi = loop where loop stream = case stream of Return r -> Return r Effect m -> Effect (fmap loop m) Step (a :> snext) -> case phi a of Nothing -> loop snext Just b -> Step (b :> loop snext) {-# INLINABLE mapMaybe #-} {-| 'slidingWindow' accumulates the first @n@ elements of a stream, update thereafter to form a sliding window of length @n@. It follows the behavior of the slidingWindow function in . >>> S.print $ S.slidingWindow 4 $ S.each "123456" fromList "1234" fromList "2345" fromList "3456" -} slidingWindow :: Monad m => Int -> Stream (Of a) m b -> Stream (Of (Seq.Seq a)) m b slidingWindow n = setup (max 1 n :: Int) mempty where window !sequ str = do e <- lift (next str) case e of Left r -> return r Right (a,rest) -> do yield (sequ Seq.|> a) window (Seq.drop 1 $ sequ Seq.|> a) rest setup 0 !sequ str = do yield sequ window (Seq.drop 1 sequ) str setup m sequ str = do e <- lift $ next str case e of Left r -> yield sequ >> return r Right (x,rest) -> setup (m-1) (sequ Seq.|> x) rest {-# INLINABLE slidingWindow #-} -- | Map monadically over a stream, producing a new stream -- only containing the 'Just' values. mapMaybeM :: Monad m => (a -> m (Maybe b)) -> Stream (Of a) m r -> Stream (Of b) m r mapMaybeM phi = loop where loop stream = case stream of Return r -> Return r Effect m -> Effect (fmap loop m) Step (a :> snext) -> Effect $ flip fmap (phi a) $ \x -> case x of Nothing -> loop snext Just b -> Step (b :> loop snext) {-# INLINABLE mapMaybeM #-}