a9a7ea3 · streamly · git.iko.soy

git.iko.soy/streamly

Merge pull request #36 from Abhiroop/iterate

Iterate

commita9a7ea3aee2f7297dd0a6dd2d859ce3546ae90b3 authorHarendra Kumar <harendra.kumar@gmail.com> dateSun 25 Mar 2018, 03:15 (9 years ago) parent398022e 9cac526

3 files changed+29−1

compare with master

unifiedsplit

Changelog.md+1 src/Streamly/Prelude.hs+18−1 test/Main.hs+10

Changelog.md+1

@@ -1,4 +1,5 @@

11## Unreleased

2+* Add `iterate`, `iterateM` stream operations

34### Bug Fixes

45* Fix Zip/AsyncZip applicative instances to handle applicative injection of function like `pure f <*> s1 <*> s2`

src/Streamly/Prelude.hs+18−1

@@ -24,6 +24,8 @@ module Streamly.Prelude

2424 , unfoldr

2525 , unfoldrM

2626 , each

27+ , iterate

28+ , iterateM

2729

2830 -- * Elimination

2931 -- ** General Folds

@@ -85,7 +87,8 @@ import Prelude hiding (filter, drop, dropWhile, take,

8587 mapM, mapM_, sequence, all, any,

8688 sum, product, elem, notElem,

8789 maximum, minimum, head, last,

88− tail, length, null, reverse)

90+ tail, length, null, reverse,

91+ iterate)

8992import qualified Prelude

9093import qualified System.IO as IO

9194

@@ -120,6 +123,20 @@ unfoldrM step = fromStream . go

120123each :: (Streaming t, Foldable f) => f a -> t m a

121124each = Prelude.foldr cons nil

122125

126+-- | Iterate a pure function from a seed value, streaming the results forever

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

128+iterate step = fromStream . go

129+ where

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

131+

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

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

134+iterateM step = fromStream . go

135+ where

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

137+ a <- step s

138+ yld s (Just (go a))

139+

123140-- | Read lines from an IO Handle into a stream of Strings.

124141fromHandle :: (Streaming t, MonadIO m) => IO.Handle -> t m String

125142fromHandle h = fromStream go

test/Main.hs+10

@@ -651,6 +651,16 @@ streamOperations (stream, list, len) = do

651651 return $ str == lst

652652 `shouldReturn` True

653653

654+ it "iterate" $

655+ (A.toList . serially . (A.take len) $ (A.iterate (+ 1) (0 :: Int)))

656+ `shouldReturn` (take len $ iterate (+ 1) 0)

657+

658+ it "iterateM" $ do

659+ let addM = (\ y -> return (y + 1))

660+ A.toList . serially . (A.take len) $ A.iterateM addM (0 :: Int)

661+ `shouldReturn` (take len $ iterate (+ 1) 0)

662+

663+

654664 -- Filtering

655665 it "filter all out" $ transform (A.filter (> len)) (filter (> len))

656666 it "filter all in" $ transform (A.filter (<= len)) (filter (<= len))