60d13da · streamly · git.iko.soy

git.iko.soy/streamly

add mapMaybe combinator in Fold

Add benchmarking and test case for mapMaybe combinator of Data.Fold Fix review comments

commit60d13da0d65b7f193b22050d6efacba44b478096 authorRanjeet Ranjan <ranjeetr@composewell.com> dateSat 17 Oct 2020, 15:06 (6 years ago) parent9444e3e

3 files changed+23−1

compare with master

unifiedsplit

benchmark/Streamly/Benchmark/Data/Fold.hs+7 src/Streamly/Internal/Data/Fold.hs+12−1 test/Streamly/Test/Data/Fold.hs+4

benchmark/Streamly/Benchmark/Data/Fold.hs+7

@@ -159,6 +159,13 @@ o_1_space_serial_transformation value =

159159 [ bgroup "serially"

160160 [ bgroup "transformation"

161161 [ benchIOSink value "lmap" (S.fold (IFL.lmap (+ 1) FL.drain))

162+ , benchIOSink

163+ value

164+ "mapMaybe"

165+ (S.fold

166+ (IFL.mapMaybe

167+ (\x -> case x of 1 -> Just x ; _ -> Nothing)

168+ FL.drain))

162169 , benchIOSink

163170 value

164171 "sequence"

src/Streamly/Internal/Data/Fold.hs+12−1

@@ -102,7 +102,7 @@ module Streamly.Internal.Data.Fold

102102 -- , ldeleteBy

103103 -- , luniq

104104 , lcatMaybes

105−

105+ , mapMaybe

106106 {-

107107 -- ** Mapping Filters

108108 , lmapMaybe

@@ -208,6 +208,7 @@ import Control.Monad.IO.Class (MonadIO(..))

208208import Data.Functor.Identity (Identity(..))

209209import Data.Int (Int64)

210210import Data.Map.Strict (Map)

211+import Data.Maybe (isJust, fromJust)

211212#if __GLASGOW_HASKELL__ < 804

212213import Data.Semigroup (Semigroup((<>)))

213214#endif

@@ -314,6 +315,16 @@ sequence (Fold step initial extract) = Fold step initial extract'

314315mapM :: Monad m => (b -> m c) -> Fold m a b -> Fold m a c

315316mapM f = sequence . fmap f

316317

318+-- | @(mapMaybe f fold)@ maps a 'Maybe' returning function @f@ on the input of the fold,

319+-- filter out the 'Nothing' elements, and return a values extracted from 'Just'.

320+-- >>> S.fold (FL.mapMaybe (\x -> case x of 5 -> Just x ; _ -> Nothing) FL.sum)

321+-- (S.enumerateFromTo 1 10)

322+-- 5

323+-- /Internal/

324+{-# INLINE mapMaybe #-}

325+mapMaybe :: (Monad m) => (a -> Maybe b) -> Fold m b r -> Fold m a r

326+mapMaybe f = lmap f . lfilter isJust . lmap fromJust

327+

317328------------------------------------------------------------------------------

318329-- Transformations on fold inputs

319330------------------------------------------------------------------------------

test/Streamly/Test/Data/Fold.hs+4

@@ -96,6 +96,9 @@ safeLast (_:xs) = safeLast xs

9696last :: [String] -> Expectation

9797last ls = S.fold FL.last (S.fromList ls) `shouldReturn` safeLast ls

9898

99+mapMaybe :: [Int] -> Expectation

100+mapMaybe ls = S.fold (F.mapMaybe (\x -> if even x then Just x else Nothing) FL.toList)

101+ (S.fromList ls) `shouldReturn` filter even ls

99102

100103nth :: Int -> [a] -> Maybe a

101104nth idx (x:xs) = if idx == 0

@@ -213,3 +216,4 @@ main = hspec $

213216 prop "Any" $ Main.any predicate

214217 prop "And" Main.and

215218 prop "Or" Main.or

219+ prop "mapMaybe" mapMaybe