3cca597 · streamly · git.iko.soy

git.iko.soy/streamly

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optimize dropWhile and add tests

3cca597Harendra Kumar9 years ago

src/Streamly/Prelude.hs+2−5

compare with master

unifiedsplit

@@ -216,10 +216,6 @@ take n m = fromStream $ go n (toStream m)

216 yield a (Just x) = yld a (Just (go (n1 - 1) x))

217 in if n1 <= 0 then stp else (runStream m1) ctx stp yield

218

219−-- XXX This is not as efficient as it could be. We need a short circuiting at

220−-- a lower level. Compare with simple-conduit, filtering there cuts down time

221−-- due to short circuting whereas the time spent remains the same here.

222−

223-- | Include only those elements that pass a predicate.

219-- | Include only those elements that pass a predicate.

224{-# INLINE filter #-}

220{-# INLINE filter #-}

225filter :: Streaming t => (a -> Bool) -> t m a -> t m a

221filter :: Streaming t => (a -> Bool) -> t m a -> t m a

@@ -256,13 +252,14 @@ drop n m = fromStream $ go n (toStream m)

256

252

257-- | Drop elements in the stream as long as the predicate succeeds and then

253-- | Drop elements in the stream as long as the predicate succeeds and then

258-- take the rest of the stream.

254-- take the rest of the stream.

255+{-# INLINE dropWhile #-}

259dropWhile :: Streaming t => (a -> Bool) -> t m a -> t m a

256dropWhile :: Streaming t => (a -> Bool) -> t m a -> t m a

260dropWhile p m = fromStream $ go (toStream m)

257dropWhile p m = fromStream $ go (toStream m)

261 where

258 where

262 go m1 = Stream $ \ctx stp yld ->

259 go m1 = Stream $ \ctx stp yld ->

263 let yield a Nothing | p a = stp

260 let yield a Nothing | p a = stp

264 | otherwise = yld a Nothing

261 | otherwise = yld a Nothing

265− yield a (Just x) | p a = (runStream (go x)) ctx stp yield

262+ yield a (Just x) | p a = (runStream x) ctx stp yield

266 | otherwise = yld a (Just x)

263 | otherwise = yld a (Just x)

267 in (runStream m1) ctx stp yield

264 in (runStream m1) ctx stp yield

268

265

test/Main.hs+6

@@ -622,6 +622,12 @@ transformOps f = do

622 it "drop none" $ testOp (A.drop 0) (drop 0)

623 it "drop 5" $ testOp (A.drop 5) (drop 5)

624

625+ it "dropWhile true" $ testOp (A.dropWhile (const True))

626+ (dropWhile (const True))

627+ it "dropWhile false" $ testOp (A.dropWhile (const False))

628+ (dropWhile (const False))

629+ it "dropWhile < 5" $ testOp (A.dropWhile (< 5)) (dropWhile (< 5))

630+

625 it "filter all out" $ testOp (A.filter (> 10)) (filter (> 10))

631 it "filter all out" $ testOp (A.filter (> 10)) (filter (> 10))

626 it "filter all in" $ testOp (A.filter (<= 10)) (filter (<= 10))

632 it "filter all in" $ testOp (A.filter (<= 10)) (filter (<= 10))

627 it "filter even" $ testOp (A.filter even) (filter even)

633 it "filter even" $ testOp (A.filter even) (filter even)