3ae0b40 · streamly · git.iko.soy

git.iko.soy/streamly

Expose postscanl' and postscanlM'

commit3ae0b40dc7c9ba94c7cf2ccf828f3a8aee76e123 authorHarendra Kumar <harendra.kumar@gmail.com> dateWed 19 Jun 2019, 21:09 (7 years ago) parent24b044a

3 files changed+14−23

compare with master

unifiedsplit

Changelog.md+1 src/Streamly/Prelude.hs+13−14 src/Streamly/Streams/StreamD.hs−9

Changelog.md+1

@@ -63,6 +63,7 @@ example, concat streams concurrently using this.

6363* Add the following to `Streamly.Prelude`:

6464 * `foldrS` to fold a stream to a stream

6565 * `foldrT` to fold a stream to an arbitrary transformer monad

66+ * `postscanl'` and `postscanlM'`

6667 * `reverse'` a several times faster reverse using Storable instance

6768 * `intersperseByTime` intersperse a mondadic action in a stream

6869 periodically

src/Streamly/Prelude.hs+13−14

@@ -313,8 +313,8 @@ module Streamly.Prelude

313313

314314 , scanl'

315315 , scanlM'

316− -- , postscanl'

317− -- , postscanlM'

316+ , postscanl'

317+ , postscanlM'

318318 -- , prescanl'

319319 -- , prescanlM'

320320 , scanl1'

@@ -1659,23 +1659,22 @@ scanlM' step begin m = fromStreamD $ D.scanlM' step begin $ toStreamD m

16591659scanl' :: (IsStream t, Monad m) => (b -> a -> b) -> b -> t m a -> t m b

16601660scanl' step z m = fromStreamS $ S.scanl' step z $ toStreamS m

16611661

1662−-- XXX enable once the signature (monadic zero) change is settled

1663−-- | Like scanl' but does not stream the initial value of the accumulator.

1662+-- | Like 'scanl'' but does not stream the initial value of the accumulator.

16641663--

1665−-- > postscanl' f z xs = S.drop 1 $ scanl' f z xs

1664+-- > postscanl' f z xs = S.drop 1 $ S.scanl' f z xs

16661665--

1667−-- @since 0.6.0

1668−{-# INLINE _postscanl' #-}

1669−_postscanl' :: (IsStream t, Monad m) => (b -> a -> b) -> b -> t m a -> t m b

1670−_postscanl' step z m = fromStreamD $ D.postscanl' step z $ toStreamD m

1666+-- @since 0.7.0

1667+{-# INLINE postscanl' #-}

1668+postscanl' :: (IsStream t, Monad m) => (b -> a -> b) -> b -> t m a -> t m b

1669+postscanl' step z m = fromStreamD $ D.postscanl' step z $ toStreamD m

16711670

16721671-- XXX this needs to be concurrent

1673−-- | Like postscanl' but with a monadic step function.

1672+-- | Like 'postscanl'' but with a monadic step function.

16741673--

1675−-- @since 0.6.0

1676−{-# INLINE _postscanlM' #-}

1677−_postscanlM' :: (IsStream t, Monad m) => (b -> a -> m b) -> b -> t m a -> t m b

1678−_postscanlM' step z m = fromStreamD $ D.postscanlM' step z $ toStreamD m

1674+-- @since 0.7.0

1675+{-# INLINE postscanlM' #-}

1676+postscanlM' :: (IsStream t, Monad m) => (b -> a -> m b) -> b -> t m a -> t m b

1677+postscanlM' step z m = fromStreamD $ D.postscanlM' step z $ toStreamD m

16791678

16801679-- XXX prescanl does not sound very useful, enable only if there is a

16811680-- compelling use case.

src/Streamly/Streams/StreamD.hs−9

@@ -1912,15 +1912,6 @@ scanlx' fstep begin done s =

19121912-- postscans

19131913------------------------------------------------------------------------------

19141914

1915−-- XXX if we make the initial value of the accumulator monadic then should we

1916−-- execute it even if the stream is empty? In that case we would have generated

1917−-- the effect but discarded the value, but that is what a fold does when the

1918−-- stream is empty. Whatever we decide, need to reconcile this with prescan.

1919−-- If we execute the initial value here without even using it then it is ok to

1920−-- execute the last step there as well without using the value.

1921−-- Looking at the duality with right fold, in case of right fold we always

1922−-- perform the action when the construction terminates, so in case of left fold

1923−-- we should perform it only when the reduction starts.

19241915{-# INLINE_NORMAL postscanlM' #-}

19251916postscanlM' :: Monad m => (b -> a -> m b) -> b -> Stream m a -> Stream m b

19261917postscanlM' fstep begin (Stream step state) =