c7b9463 · streamly · git.iko.soy

git.iko.soy/streamly

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Add the monadic iterate function

c7b9463Abhiroop Sarkar9 years ago

Changelog.md+1−1

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

8### Enhancements

9* 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

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

13### Bug Fixes

src/Streamly/Prelude.hs+9−1

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

25 , unfoldrM

26 , each

27 , iterate

28+ , iterateM

29 -- * Elimination

30 -- * Elimination

30 -- ** General Folds

31 -- ** General Folds

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

126iterate :: Streaming t => (a -> a) -> a -> t m a

127iterate :: Streaming t => (a -> a) -> a -> t m a

127iterate step = fromStream . go

128iterate step = fromStream . go

128 where

129 where

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

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

130

131

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)))

131

139

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

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

133fromHandle :: (Streaming t, MonadIO m) => IO.Handle -> t m String

141fromHandle :: (Streaming t, MonadIO m) => IO.Handle -> t m String