c7b9463 · streamly · git.iko.soy

git.iko.soy/streamly

Add the monadic iterate function

commitc7b94637c91a464ca6dd3a0875b143264a2450e1 authorAbhiroop Sarkar <asiamgenius@gmail.com> dateThu 22 Mar 2018, 22:33 (9 years ago) parent4a6f946

2 files changed+10−2

unifiedsplit

Changelog.md+1−1

@@ -7,7 +7,7 @@

88### Enhancements

99* Make `cons` right associative and provide an operator form `.:` for it

10−* Add `iterate`, `null`, `tail`, `reverse`, `replicateM`, `scan` stream operations

10+* Add `iterateM`, `iterate`, `null`, `tail`, `reverse`, `replicateM`, `scan` stream operations

1111* Improve performance of some stream operations (`foldl`, `dropWhile`)

1212

1313### Bug Fixes

src/Streamly/Prelude.hs+9−1

@@ -25,6 +25,7 @@ module Streamly.Prelude

2525 , unfoldrM

2626 , each

2727 , iterate

28+ , iterateM

2829

2930 -- * Elimination

3031 -- ** General Folds

@@ -126,8 +127,15 @@ each = Prelude.foldr cons nil

126127iterate :: Streaming t => (a -> a) -> a -> t m a

127128iterate step = fromStream . go

128129 where

129− go s = scons s (Just (go (step s)))

130+ go s = scons s (Just (go (step s)))

130131

132+-- | Iterate a monadic function from a seed value, streaming the results forever

133+iterateM :: (Streaming t, Monad m) => (a -> m a) -> m a -> t m a

134+iterateM step = fromStream . go

135+ where

136+ go ms = Stream $ \_ _ yld -> do

137+ s <- ms

138+ yld s (Just (go (step s)))

131139

132140-- | Read lines from an IO Handle into a stream of Strings.

133141fromHandle :: (Streaming t, MonadIO m) => IO.Handle -> t m String