41e9492 · streamly · git.iko.soy

git.iko.soy/streamly

Add headElse

commit41e94929564e69473dccbe82477ba175fd514962 authorHarendra Kumar <harendra.kumar@gmail.com> dateSat 23 Nov 2019, 17:03 (7 years ago) parent35ba2c3

2 files changed+15

compare with master

unifiedsplit

src/Streamly/Internal/Prelude.hs+10 src/Streamly/Streams/StreamD.hs+5

src/Streamly/Internal/Prelude.hs+10

@@ -104,6 +104,7 @@ module Streamly.Internal.Prelude

104104 -- -- | Folds that extract selected elements of a stream or their properties.

105105 , (!!)

106106 , head

107+ , headElse

107108 , findM

108109 , find

109110 , lookup

@@ -1115,6 +1116,15 @@ null = S.null . toStreamS

11151116head :: Monad m => SerialT m a -> m (Maybe a)

11161117head = S.head . toStreamS

11171118

1119+-- | Extract the first element of the stream, if any, otherwise use the

1120+-- supplied default value. It can help avoid one branch in high performance

1121+-- code.

1122+--

1123+-- /Internal/

1124+{-# INLINE headElse #-}

1125+headElse :: Monad m => a -> SerialT m a -> m a

1126+headElse x = D.headElse x . toStreamD

1127+

11181128-- |

11191129-- > tail = fmap (fmap snd) . uncons

11201130--

src/Streamly/Streams/StreamD.hs+5

@@ -122,6 +122,7 @@ module Streamly.Streams.StreamD

122122 , drain

123123 , null

124124 , head

125+ , headElse

125126 , tail

126127 , last

127128 , elem

@@ -896,6 +897,10 @@ null m = foldrM (\_ _ -> return False) (return True) m

896897head :: Monad m => Stream m a -> m (Maybe a)

897898head m = foldrM (\x _ -> return (Just x)) (return Nothing) m

898899

900+{-# INLINE_NORMAL headElse #-}

901+headElse :: Monad m => a -> Stream m a -> m a

902+headElse a m = foldrM (\x _ -> return x) (return a) m

903+

899904-- Does not fuse, has the same performance as the StreamK version.

900905{-# INLINE_NORMAL tail #-}

901906tail :: Monad m => Stream m a -> m (Maybe (Stream m a))