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authorharendra <>2018-03-18 14:56:00 (GMT)
committerhdiff <hdiff@hdiff.luite.com>2018-03-18 14:56:00 (GMT)
commit83183a57cd05584bb23cbe70c01fb81b3b2b1a09 (patch)
tree20e9b5501b42ef62f3986f7af4b3feb6965b3f90
parent9c09b5a4974f1be31231c759ba70e00ae4d8446a (diff)
version 0.1.10.1.1
-rw-r--r--Changelog.md11
-rw-r--r--README.md61
-rw-r--r--src/Streamly/Core.hs115
-rw-r--r--src/Streamly/Prelude.hs199
-rw-r--r--src/Streamly/Streams.hs57
-rw-r--r--src/Streamly/Time.hs2
-rw-r--r--src/Streamly/Tutorial.hs5
-rw-r--r--stack-8.0.yaml17
-rw-r--r--stack.yaml4
-rw-r--r--streamly.cabal15
-rw-r--r--test/Main.hs158
11 files changed, 461 insertions, 183 deletions
diff --git a/Changelog.md b/Changelog.md
index 1318780..b8c9865 100644
--- a/Changelog.md
+++ b/Changelog.md
@@ -1,3 +1,14 @@
+## 0.1.1
+
+### Enhancements
+* Make `cons` right associative and provide an operator form `.:` for it
+* Add `null`, `tail`, `reverse`, `replicateM`, `scan` stream operations
+* Improve performance of some stream operations (`foldl`, `dropWhile`)
+
+### Bug Fixes
+* Fix the `product` operation. Earlier, it always returned 0 due to a bug
+* Fix the `last` operation, which returned `Nothing` for singleton streams
+
## 0.1.0
* Initial release
diff --git a/README.md b/README.md
index 1d8d0ff..61453cb 100644
--- a/README.md
+++ b/README.md
@@ -1,10 +1,5 @@
# Streamly
-[![Gitter chat](https://badges.gitter.im/composewell/gitter.svg)](https://gitter.im/composewell/streamly)
-[![Build Status](https://travis-ci.org/composewell/streamly.svg?branch=master)](https://travis-ci.org/composewell/streamly)
-[![Windows Build status](https://ci.appveyor.com/api/projects/status/ajxg0c79raou9ned?svg=true)](https://ci.appveyor.com/project/harendra-kumar/streamly)
-[![Coverage Status](https://coveralls.io/repos/composewell/streamly/badge.svg?branch=master&service=github)](https://coveralls.io/github/composewell/streamly?branch=master)
-
## Stream`ing` `Concurrent`ly
Streamly is a monad transformer unifying non-determinism
@@ -23,14 +18,23 @@ See the haddock documentation for full reference. It is recommended to read
the comprehensive tutorial module `Streamly.Tutorial` first. Also see
`Streamly.Examples` for some working examples.
+`Streamly` has best in class performance even though it generalizes streaming
+to concurrent composition that does not mean it sacrifices non-concurrent
+performance. See
+[streaming-benchmarks](https://github.com/composewell/streaming-benchmarks) for
+detailed performance comparison with regular streaming libraries.
+
## Non-determinism
The monad instance composes like a list monad.
``` haskell
-loops = $ do
- x <- each [1,2]
- y <- each [3,4]
+import Streamly
+import qualified Streamly.Prelude as S
+
+loops = do
+ x <- S.each [1,2]
+ y <- S.each [3,4]
liftIO $ putStrLn $ show (x, y)
main = runStreaming $ serially $ loops
@@ -68,13 +72,17 @@ You can fold multiple streams or IO actions using parallel combinators like
concurrently sum the square roots of all combinations:
``` haskell
+import Streamly
+import qualified Streamly.Prelude as S
+
main = do
- print $ sum $ asyncly $ do
- -- Squaring is concurrent (<|)
- x2 <- forEachWith (<|) [1..100] $ \x -> return $ x * x
- y2 <- forEachWith (<|) [1..100] $ \y -> return $ y * y
- -- sqrt is concurrent (asyncly)
- return $ sqrt (x2 + y2)
+ s <- S.sum $ asyncly $ do
+ -- Squaring is concurrent (<|)
+ x2 <- forEachWith (<|) [1..100] $ \x -> return $ x * x
+ y2 <- forEachWith (<|) [1..100] $ \y -> return $ y * y
+ -- sqrt is concurrent (asyncly)
+ return $ sqrt (x2 + y2)
+ print s
```
Of course, the actions running in parallel could be arbitrary IO actions. To
@@ -116,7 +124,7 @@ therefore, no special operator is needed to join stream stages, just a forward
```haskell
import Streamly
-import Streamly.Prelude as S
+import qualified Streamly.Prelude as S
import Data.Function ((&))
main = S.each [1..10]
@@ -143,11 +151,13 @@ main = S.each [1..10]
Streams can be combined together in multiple ways:
```haskell
-return 1 <> return 2 -- serial, combine atoms
-S.each [1..10] <> S.each [11..20] -- serial
-S.each [1..10] <| S.each [11..20] -- demand driven parallel
-S.each [1..10] <=> S.each [11..20] -- serial but interleaved
-S.each [1..10] <|> S.each [11..20] -- fully parallel
+main = do
+ let p s = (toList . serially) s >>= print
+ p $ return 1 <> return 2 -- serial, combine atoms
+ p $ S.each [1..10] <> S.each [11..20] -- serial
+ p $ S.each [1..10] <| S.each [11..20] -- demand driven parallel
+ p $ S.each [1..10] <=> S.each [11..20] -- serial but interleaved
+ p $ S.each [1..10] <|> S.each [11..20] -- fully parallel
```
As we have already seen streams can be combined using monadic composition in a
@@ -163,10 +173,13 @@ and `Streamly.Examples.CirclingSquare` for an SDL based animation example.
## Contributing
-The code is available under BSD-3 license [on
-github](https://github.com/composewell/streamly). Join the [gitter
-chat](https://gitter.im/composewell/streamly) channel for discussions. All
-contributions are welcome!
+The code is available under BSD-3 license
+[on github](https://github.com/composewell/streamly). Join the
+[gitter chat](https://gitter.im/composewell/streamly) channel for discussions.
+You can find some of the
+[todo items on the github wiki](https://github.com/composewell/streamly/wiki/Things-To-Do).
+Please ask on the gitter channel or [contact the maintainer directly](mailto:harendra.kumar@gmail.com)
+for more details on each item. All contributions are welcome!
This library was originally inspired by the `transient` package authored by
Alberto G. Corona.
diff --git a/src/Streamly/Core.hs b/src/Streamly/Core.hs
index 5663ec5..7ed7362 100644
--- a/src/Streamly/Core.hs
+++ b/src/Streamly/Core.hs
@@ -1,6 +1,7 @@
{-# LANGUAGE ConstraintKinds #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE LambdaCase #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE RankNTypes #-}
{-# LANGUAGE UndecidableInstances #-} -- XXX
@@ -89,7 +90,7 @@ data ChildEvent a =
------------------------------------------------------------------------------
-- | Conjunction is used for monadic/product style composition. Disjunction is
--- used for fold/sum style composition. We need to distiguish the two types of
+-- used for fold/sum style composition. We need to distinguish the two types of
-- SVars so that the scheduling of the two is independent.
data SVarTag = Conjunction | Disjunction deriving Eq
@@ -140,13 +141,65 @@ data SVar m a =
------------------------------------------------------------------------------
-- TBD use a functor instead of the bare type a?
--- XXX remove the Maybe, use "empty" as the base case
--- | Represents a monadic stream of values of type 'a' constructed using
--- actions in monad 'm'. Streams can be composed sequentially or in parallel;
--- in product style compositions (monadic bind multiplies streams in a ListT
--- fashion) or in sum style compositions like 'Semigroup', 'Monoid',
--- 'Alternative' or variants of these.
+-- | The type 'Stream m a' represents a monadic stream of values of type 'a'
+-- constructed using actions in monad 'm'. It uses a stop continuation and a
+-- yield continuation. You can consider it a rough equivalent of direct style
+-- type:
+--
+-- data Stream m a = Stop | Yield a (Maybe (Stream m a))
+--
+-- Our goal is to be able to represent finite as well infinite streams and
+-- being able to compose a large number of small streams efficiently. In
+-- addition we want to compose streams in parallel, to facilitate that we
+-- maintain a local state in an SVar that is shared across and is used for
+-- synchronization of the streams being composed.
+--
+-- Using this type, there are two ways to indicate the end of a stream, one is
+-- by calling the stop continuation and the other one is by yielding the last
+-- value along with 'Nothing' as the rest of the stream.
+--
+-- Why do we have this redundancy? Why can't we use (a -> Stream m a -> m r) as
+-- the type of the yield continuation and always use the stop continuation to
+-- indicate the end of the stream? The reason is that when we compose a large
+-- number of short or singleton streams then using the stop continuation
+-- becomes expensive, just to know that there is no next element we have to
+-- call the continuation, introducing an indirection, it seems when using CPS
+-- GHC is not able to optimize this out as efficiently as it can be in direct
+-- style because of the function call involved. In direct style it will just be
+-- a constructor check and a memory access instead of a function call. So we
+-- could use:
+--
+-- data Stream m a = Stop | Yield a (Stream m a)
+--
+-- In CPS style, when we use the 'Maybe' argument of yield to indicate the end
+-- then just like direct style we can figure out that there is no next element
+-- without a function call.
+--
+-- Then why not get rid of the stop continuation and use only yield to indicate
+-- the end of stream? The answer is, in that case to indicate the end of the
+-- stream we would have to yield at least one element so there is no way to
+-- represent an empty stream.
+--
+-- Whenever we make a singleton stream or in general when we build a stream
+-- strictly i.e. when we know all the elements of the stream in advance we can
+-- use the last yield to indicate th end of the stream, because we know in
+-- advance at the time of the last yield that the stream is ending. We build
+-- singleton streams in the implementation of 'pure' for Applicative and Monad,
+-- and in 'lift' for MonadTrans, in these places we use yield with 'Nothing' to
+-- indicate the end of the stream. Note that, the only advantage of Maybe is
+-- when we have to build a large number of singleton or short streams. For
+-- larger streams anyway the overhead of a separate stop continuation is not
+-- significant. This could be significant when we breakdown a large stream into
+-- its elements, process them in some way and then recompose it from the
+-- pieces. Zipping streams is one such example. Zipping with streamly is the
+-- fastest among all streaming libraries.
+--
+-- However in a lazy computation we cannot know in advance that the stream is
+-- ending therefore we cannot use 'Maybe', we use the stop continuation in that
+-- case. For example when building a stream from a lazy container using a right
+-- fold.
+--
newtype Stream m a =
Stream {
runStream :: forall r.
@@ -168,6 +221,15 @@ snil :: Stream m a
snil = Stream $ \_ stp _ -> stp
------------------------------------------------------------------------------
+-- Composing streams
+------------------------------------------------------------------------------
+
+-- Streams can be composed sequentially or in parallel; in product style
+-- compositions (monadic bind multiplies streams in a ListT fashion) or in sum
+-- style compositions like 'Semigroup', 'Monoid', 'Alternative' or variants of
+-- these.
+
+------------------------------------------------------------------------------
-- Semigroup
------------------------------------------------------------------------------
@@ -253,10 +315,9 @@ runqueueLIFO sv q = run
yield a Nothing = sendit a >> run
yield a (Just r) = sendit a >> (runStream r) (Just sv) run yield
- dequeue = liftIO $ atomicModifyIORefCAS q $ \ ms ->
- case ms of
- [] -> ([], Nothing)
- x : xs -> (xs, Just x)
+ dequeue = liftIO $ atomicModifyIORefCAS q $ \case
+ [] -> ([], Nothing)
+ x : xs -> (xs, Just x)
{-# INLINE enqueueFIFO #-}
enqueueFIFO :: LinkedQueue (Stream m a) -> Stream m a -> IO ()
@@ -289,7 +350,7 @@ runqueueFIFO sv q = run
{-# NOINLINE addThread #-}
addThread :: MonadIO m => SVar m a -> ThreadId -> m ()
addThread sv tid =
- liftIO $ modifyIORef (runningThreads sv) $ (\s -> S.insert tid s)
+ liftIO $ modifyIORef (runningThreads sv) (S.insert tid)
{-# INLINE delThread #-}
delThread :: MonadIO m => SVar m a -> ThreadId -> m ()
@@ -298,8 +359,7 @@ delThread sv tid =
{-# INLINE allThreadsDone #-}
allThreadsDone :: MonadIO m => SVar m a -> m Bool
-allThreadsDone sv = liftIO $ do
- readIORef (runningThreads sv) >>= return . S.null
+allThreadsDone sv = liftIO $ S.null <$> readIORef (runningThreads sv)
{-# NOINLINE handleChildException #-}
handleChildException :: MonadIO m => SVar m a -> SomeException -> m ()
@@ -326,8 +386,8 @@ sendWorkerWait sv = do
output <- liftIO $ readIORef (outputQueue sv)
when (null output) $ do
done <- queueEmpty sv
- if (not done)
- then (pushWorker sv) >> sendWorkerWait sv
+ if not done
+ then pushWorker sv >> sendWorkerWait sv
else void (liftIO $ takeMVar (doorBell sv))
-- | Pull a stream from an SVar.
@@ -381,13 +441,13 @@ getFifoSVar ctype = do
running <- newIORef S.empty
q <- newQ
let sv =
- SVar { outputQueue = outQ
+ SVar { outputQueue = outQ
, doorBell = outQMv
, runningThreads = running
, runqueue = runqueueFIFO sv q
, enqueue = pushL q
, queueEmpty = liftIO $ nullQ q
- , svarStyle = ctype
+ , svarStyle = ctype
}
in return sv
@@ -397,30 +457,25 @@ getLifoSVar ctype = do
outQMv <- newEmptyMVar
running <- newIORef S.empty
q <- newIORef []
- let checkEmpty = liftIO (readIORef q) >>= return . null
+ let checkEmpty = null <$> liftIO (readIORef q)
let sv =
- SVar { outputQueue = outQ
+ SVar { outputQueue = outQ
, doorBell = outQMv
, runningThreads = running
, runqueue = runqueueLIFO sv q
, enqueue = enqueueLIFO q
, queueEmpty = checkEmpty
- , svarStyle = ctype
+ , svarStyle = ctype
}
in return sv
-- | Create a new empty SVar.
newEmptySVar :: MonadAsync m => SVarStyle -> m (SVar m a)
newEmptySVar style = do
- sv <- liftIO $
+ liftIO $
case style of
- SVarStyle _ FIFO -> do
- c <- getFifoSVar style
- return c
- SVarStyle _ LIFO -> do
- c <- getLifoSVar style
- return c
- return sv
+ SVarStyle _ FIFO -> getFifoSVar style
+ SVarStyle _ LIFO -> getLifoSVar style
-- | Create a new SVar and enqueue one stream computation on it.
newStreamVar1 :: MonadAsync m => SVarStyle -> Stream m a -> m (SVar m a)
@@ -534,7 +589,7 @@ withNewSVar2 style m1 m2 = Stream $ \_ stp yld -> do
{-# INLINE joinStreamVar2 #-}
joinStreamVar2 :: MonadAsync m
=> SVarStyle -> Stream m a -> Stream m a -> Stream m a
-joinStreamVar2 style m1 m2 = Stream $ \st stp yld -> do
+joinStreamVar2 style m1 m2 = Stream $ \st stp yld ->
case st of
Just sv | svarStyle sv == style ->
liftIO ((enqueue sv) m2) >> (runStream m1) st stp yld
diff --git a/src/Streamly/Prelude.hs b/src/Streamly/Prelude.hs
index 0871526..57a727c 100644
--- a/src/Streamly/Prelude.hs
+++ b/src/Streamly/Prelude.hs
@@ -1,10 +1,8 @@
{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE FlexibleInstances #-}
-{-# LANGUAGE GeneralizedNewtypeDeriving#-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE RankNTypes #-}
-{-# LANGUAGE StandaloneDeriving #-}
{-# LANGUAGE UndecidableInstances #-} -- XXX
-- |
@@ -20,34 +18,38 @@
module Streamly.Prelude
(
-- * Construction
- cons
- , nil
+ nil
+ , cons
+ , (.:)
, unfoldr
, unfoldrM
, each
- , fromHandle
-- * Elimination
+ -- ** General Folds
, foldr
, foldrM
+ , scan
, foldl
, foldlM
, uncons
- -- * Elimination Special Folds
+ -- ** Special Folds
, toList
- , toHandle
, all
, any
- , sum
- , product
, head
+ , tail
, last
+ , null
, length
, elem
, notElem
+ , reverse
, maximum
, minimum
+ , sum
+ , product
-- * Filtering
, filter
@@ -60,16 +62,22 @@ module Streamly.Prelude
, mapM
, mapM_
, sequence
+ , replicateM
-- * Zipping
, zipWith
, zipWithM
, zipAsyncWith
, zipAsyncWithM
+
+ -- * IO
+ , fromHandle
+ , toHandle
+
)
where
-import Control.Monad (liftM)
+import Control.Monad (void)
import Control.Monad.IO.Class (MonadIO(..))
import Data.Semigroup (Semigroup(..))
import Prelude hiding (filter, drop, dropWhile, take,
@@ -77,13 +85,12 @@ import Prelude hiding (filter, drop, dropWhile, take,
mapM, mapM_, sequence, all, any,
sum, product, elem, notElem,
maximum, minimum, head, last,
- length)
-import qualified Prelude as Prelude
+ tail, length, null, reverse)
+import qualified Prelude
import qualified System.IO as IO
import Streamly.Core
import Streamly.Streams
-
------------------------------------------------------------------------------
-- Construction
------------------------------------------------------------------------------
@@ -92,7 +99,7 @@ import Streamly.Streams
unfoldr :: Streaming t => (b -> Maybe (a, b)) -> b -> t m a
unfoldr step = fromStream . go
where
- go s = Stream $ \_ stp yld -> do
+ go s = Stream $ \_ stp yld ->
case step s of
Nothing -> stp
Just (a, b) -> yld a (Just (go b))
@@ -110,12 +117,12 @@ unfoldrM step = fromStream . go
-- XXX need eachInterleaved, eachAsync, eachParallel
-- | Same as @foldWith (<>)@ but more efficient.
{-# INLINE each #-}
-each :: (Foldable f, Streaming t) => f a -> t m a
-each xs = Prelude.foldr cons nil xs
+each :: (Streaming t, Foldable f) => f a -> t m a
+each = Prelude.foldr cons nil
-- | Read lines from an IO Handle into a stream of Strings.
-fromHandle :: (MonadIO m, Streaming t) => IO.Handle -> t m String
-fromHandle h = fromStream $ go
+fromHandle :: (Streaming t, MonadIO m) => IO.Handle -> t m String
+fromHandle h = fromStream go
where
go = Stream $ \_ stp yld -> do
eof <- liftIO $ IO.hIsEOF h
@@ -132,7 +139,7 @@ fromHandle h = fromStream $ go
-- Parallel variants of folds?
-- | Right fold.
-foldr :: (Monad m, Streaming t) => (a -> b -> b) -> b -> t m a -> m b
+foldr :: (Streaming t, Monad m) => (a -> b -> b) -> b -> t m a -> m b
foldr step acc m = go (toStream m)
where
go m1 =
@@ -152,21 +159,49 @@ foldrM step acc m = go (toStream m)
yield a (Just x) = step a (go x)
in (runStream m1) Nothing stop yield
+-- | Scan left. A strict left fold which accumulates the result of its reduction steps inside a stream, from left.
+{-# INLINE scan #-}
+scan :: Streaming t => (x -> a -> x) -> x -> (x -> b) -> t m a -> t m b
+scan step begin done m = cons (done begin) $ fromStream $ go (toStream m) begin
+ where
+ go m1 !acc = Stream $ \_ stp yld ->
+ let stop = stp
+ yield a Nothing = yld (done $ step acc a) Nothing
+ yield a (Just x) =
+ let s = step acc a
+ in yld (done s) (Just (go x s))
+ in runStream m1 Nothing stop yield
+
-- | Strict left fold. This is typed to work with the foldl package. To use
--- directly pass 'id' as the third argument.
-foldl :: (Monad m, Streaming t)
+-- it normally just pass 'id' as the third argument.
+{-# INLINE foldl #-}
+foldl :: (Streaming t, Monad m)
=> (x -> a -> x) -> x -> (x -> b) -> t m a -> m b
-foldl step begin done m = go begin (toStream m)
+foldl step begin done m = get $ go (toStream m) begin
where
- go !acc m1 =
- let stop = return (done acc)
- yield a Nothing = return (done (step acc a))
- yield a (Just x) = go (step acc a) x
- in (runStream m1) Nothing stop yield
+ {-# NOINLINE get #-}
+ get m1 =
+ let yield a Nothing = return $ done a
+ yield _ _ = undefined
+ in (runStream m1) Nothing undefined yield
+
+ -- Note, this can be implemented by making a recursive call to "go",
+ -- however that is more expensive because of unnecessary recursion
+ -- that cannot be tail call optimized. Unfolding recursion explicitly via
+ -- continuations is much more efficient.
+ go m1 !acc = Stream $ \_ _ yld ->
+ let stop = yld acc Nothing
+ yield a r =
+ let s = step acc a
+ in case r of
+ Nothing -> yld s Nothing
+ Just x -> (runStream (go x s)) Nothing undefined yld
+ in (runStream m1) Nothing stop yield
+-- XXX replace the recursive "go" with explicit continuations.
-- | Strict left fold, with monadic step function. This is typed to work
-- with the foldl package. To use directly pass 'id' as the third argument.
-foldlM :: (Monad m, Streaming t)
+foldlM :: (Streaming t, Monad m)
=> (x -> a -> m x) -> m x -> (x -> m b) -> t m a -> m b
foldlM step begin done m = go begin (toStream m)
where
@@ -183,7 +218,7 @@ uncons :: (Streaming t, Monad m) => t m a -> m (Maybe (a, t m a))
uncons m =
let stop = return Nothing
yield a Nothing = return (Just (a, nil))
- yield a (Just x) = return (Just (a, (fromStream x)))
+ yield a (Just x) = return (Just (a, fromStream x))
in (runStream (toStream m)) Nothing stop yield
-- | Write a stream of Strings to an IO Handle.
@@ -202,34 +237,37 @@ toHandle h m = go (toStream m)
-- | Convert a stream into a list in the underlying monad.
{-# INLINABLE toList #-}
-toList :: (Monad m, Streaming t) => t m a -> m [a]
-toList = foldrM (\a xs -> liftM (a :) xs) (return [])
+toList :: (Streaming t, Monad m) => t m a -> m [a]
+toList = foldrM (\a xs -> fmap (a :) xs) (return [])
-- | Take first 'n' elements from the stream and discard the rest.
+{-# INLINE take #-}
take :: Streaming t => Int -> t m a -> t m a
take n m = fromStream $ go n (toStream m)
where
- go n1 m1 = Stream $ \ctx stp yld -> do
+ go n1 m1 = Stream $ \ctx stp yld ->
let yield a Nothing = yld a Nothing
yield a (Just x) = yld a (Just (go (n1 - 1) x))
- if (n1 <= 0)
- then stp
- else (runStream m1) ctx stp yield
-
--- XXX This is not as efficient as it could be. We need a short circuiting at
--- a lower level. Compare with simple-conduit, filtering there cuts down time
--- due to short circuting whereas the time spent remains the same here.
+ in if n1 <= 0 then stp else (runStream m1) ctx stp yield
-- | Include only those elements that pass a predicate.
{-# INLINE filter #-}
-filter :: (Streaming t, Monad (t m)) => (a -> Bool) -> t m a -> t m a
-filter p m = m >>= \x -> if p x then return x else nil
+filter :: Streaming t => (a -> Bool) -> t m a -> t m a
+filter p m = fromStream $ go (toStream m)
+ where
+ go m1 = Stream $ \ctx stp yld ->
+ let yield a Nothing | p a = yld a Nothing
+ | otherwise = stp
+ yield a (Just x) | p a = yld a (Just (go x))
+ | otherwise = (runStream x) ctx stp yield
+ in (runStream m1) ctx stp yield
-- | End the stream as soon as the predicate fails on an element.
+{-# INLINE takeWhile #-}
takeWhile :: Streaming t => (a -> Bool) -> t m a -> t m a
takeWhile p m = fromStream $ go (toStream m)
where
- go m1 = Stream $ \ctx stp yld -> do
+ go m1 = Stream $ \ctx stp yld ->
let yield a Nothing | p a = yld a Nothing
| otherwise = stp
yield a (Just x) | p a = yld a (Just (go x))
@@ -240,22 +278,24 @@ takeWhile p m = fromStream $ go (toStream m)
drop :: Streaming t => Int -> t m a -> t m a
drop n m = fromStream $ go n (toStream m)
where
- go n1 m1 = Stream $ \ctx stp yld -> do
+ go n1 m1 = Stream $ \ctx stp yld ->
let yield _ Nothing = stp
yield _ (Just x) = (runStream $ go (n1 - 1) x) ctx stp yld
- if (n1 <= 0)
- then (runStream m1) ctx stp yld
- else (runStream m1) ctx stp yield
+ -- Somehow "<=" check performs better than a ">"
+ in if n1 <= 0
+ then (runStream m1) ctx stp yld
+ else (runStream m1) ctx stp yield
-- | Drop elements in the stream as long as the predicate succeeds and then
-- take the rest of the stream.
+{-# INLINE dropWhile #-}
dropWhile :: Streaming t => (a -> Bool) -> t m a -> t m a
dropWhile p m = fromStream $ go (toStream m)
where
- go m1 = Stream $ \ctx stp yld -> do
+ go m1 = Stream $ \ctx stp yld ->
let yield a Nothing | p a = stp
| otherwise = yld a Nothing
- yield a (Just x) | p a = (runStream (go x)) ctx stp yield
+ yield a (Just x) | p a = (runStream x) ctx stp yield
| otherwise = yld a (Just x)
in (runStream m1) ctx stp yield
@@ -287,7 +327,7 @@ sum = foldl (+) 0 id
-- | Determine the product of all elements of a stream of numbers
product :: (Streaming t, Monad m, Num a) => t m a -> m a
-product = foldl (*) 0 id
+product = foldl (*) 1 id
-- | Extract the first element of the stream, if any.
head :: (Streaming t, Monad m) => t m a -> m (Maybe a)
@@ -296,15 +336,25 @@ head m =
yield a _ = return (Just a)
in (runStream (toStream m)) Nothing stop yield
+-- | Extract all but the first element of the stream, if any.
+tail :: (Streaming t, Monad m) => t m a -> m (Maybe (t m a))
+tail m =
+ let stop = return Nothing
+ yield _ Nothing = return $ Just nil
+ yield _ (Just t) = return $ Just $ fromStream t
+ in (runStream (toStream m)) Nothing stop yield
+
-- | Extract the last element of the stream, if any.
+{-# INLINE last #-}
last :: (Streaming t, Monad m) => t m a -> m (Maybe a)
-last m = go (toStream m)
- where
- go m1 =
- let stop = return Nothing
- yield a Nothing = return (Just a)
- yield _ (Just x) = go x
- in (runStream m1) Nothing stop yield
+last = foldl (\_ y -> Just y) Nothing id
+
+-- | Determine whether the stream is empty.
+null :: (Streaming t, Monad m) => t m a -> m Bool
+null m =
+ let stop = return True
+ yield _ _ = return False
+ in (runStream (toStream m)) Nothing stop yield
-- | Determine whether an element is present in the stream.
elem :: (Streaming t, Monad m, Eq a) => a -> t m a -> m Bool
@@ -313,7 +363,7 @@ elem e m = go (toStream m)
go m1 =
let stop = return False
yield a Nothing = return (a == e)
- yield a (Just x) = if (a == e) then return True else go x
+ yield a (Just x) = if a == e then return True else go x
in (runStream m1) Nothing stop yield
-- | Determine whether an element is not present in the stream.
@@ -323,13 +373,27 @@ notElem e m = go (toStream m)
go m1 =
let stop = return True
yield a Nothing = return (a /= e)
- yield a (Just x) = if (a == e) then return False else go x
+ yield a (Just x) = if a == e then return False else go x
in (runStream m1) Nothing stop yield
-- | Determine the length of the stream.
length :: (Streaming t, Monad m) => t m a -> m Int
length = foldl (\n _ -> n + 1) 0 id
+-- | Returns the elements of the stream in reverse order.
+-- The stream must be finite.
+reverse :: (Streaming t) => t m a -> t m a
+reverse m = fromStream $ go Nothing (toStream m)
+ where
+ go rev rest = Stream $ \svr stp yld ->
+ let stop = case rev of
+ Nothing -> stp
+ Just str -> runStream str svr stp yld
+ yield a Nothing = runStream (a `scons` rev) svr stp yld
+ yield a (Just x) = runStream (go (Just $ a `scons` rev) x) svr stp yld
+ in runStream rest svr stop yield
+
+-- XXX replace the recursive "go" with continuation
-- | Determine the minimum element in a stream.
minimum :: (Streaming t, Monad m, Ord a) => t m a -> m (Maybe a)
minimum m = go Nothing (toStream m)
@@ -344,6 +408,7 @@ minimum m = go Nothing (toStream m)
Nothing -> Just a
Just e -> Just $ min a e
+-- XXX replace the recursive "go" with continuation
-- | Determine the maximum element in a stream.
maximum :: (Streaming t, Monad m, Ord a) => t m a -> m (Maybe a)
maximum m = go Nothing (toStream m)
@@ -366,10 +431,11 @@ maximum m = go Nothing (toStream m)
-- | Replace each element of the stream with the result of a monadic action
-- applied on the element.
+{-# INLINE mapM #-}
mapM :: (Streaming t, Monad m) => (a -> m b) -> t m a -> t m b
mapM f m = fromStream $ go (toStream m)
where
- go m1 = Stream $ \_ stp yld -> do
+ go m1 = Stream $ \_ stp yld ->
let stop = stp
yield a Nothing = f a >>= \b -> yld b Nothing
yield a (Just x) = f a >>= \b -> yld b (Just (go x))
@@ -382,7 +448,7 @@ mapM_ f m = go (toStream m)
where
go m1 =
let stop = return ()
- yield a Nothing = f a >> return ()
+ yield a Nothing = void (f a)
yield a (Just x) = f a >> go x
in (runStream m1) Nothing stop yield
@@ -391,12 +457,21 @@ mapM_ f m = go (toStream m)
sequence :: (Streaming t, Monad m) => t m (m a) -> t m a
sequence m = fromStream $ go (toStream m)
where
- go m1 = Stream $ \_ stp yld -> do
+ go m1 = Stream $ \_ stp yld ->
let stop = stp
yield a Nothing = a >>= \b -> yld b Nothing
yield a (Just x) = a >>= \b -> yld b (Just (go x))
in (runStream m1) Nothing stop yield
+-- | Generate a stream by performing an action @n@ times.
+replicateM :: (Streaming t, Monad m) => Int -> m a -> t m a
+replicateM n m = fromStream $ go n
+ where
+ go cnt = Stream $ \_ stp yld ->
+ if cnt <= 0
+ then stp
+ else m >>= \a -> yld a (Just $ go (cnt - 1))
+
------------------------------------------------------------------------------
-- Serially Zipping Streams
------------------------------------------------------------------------------
@@ -409,7 +484,7 @@ zipWithM f m1 m2 = fromStream $ go (toStream m1) (toStream m2)
let merge a ra =
let yield2 b Nothing = (runStream (g a b)) Nothing stp yld
yield2 b (Just rb) =
- (runStream ((g a b) <> (go ra rb))) Nothing stp yld
+ (runStream (g a b <> go ra rb)) Nothing stp yld
in (runStream my) Nothing stp yield2
let yield1 a Nothing = merge a snil
yield1 a (Just ra) = merge a ra
diff --git a/src/Streamly/Streams.hs b/src/Streamly/Streams.hs
index 4a297d4..fd3a220 100644
--- a/src/Streamly/Streams.hs
+++ b/src/Streamly/Streams.hs
@@ -29,13 +29,14 @@ module Streamly.Streams
, newEmptySVar
-- * Construction
+ , nil
+ , cons
+ , (.:)
, streamBuild
, fromCallback
, fromSVar
-- * Elimination
- , cons
- , nil
, streamFold
, runStreaming
, toSVar
@@ -94,7 +95,7 @@ import Control.Monad.Reader.Class (MonadReader(..))
import Control.Monad.State.Class (MonadState(..))
import Control.Monad.Trans.Class (MonadTrans)
import Data.Semigroup (Semigroup(..))
-import Prelude hiding (drop, take, zipWith)
+import Prelude hiding (zipWith)
import Streamly.Core
------------------------------------------------------------------------------
@@ -111,13 +112,53 @@ class Streaming t where
-- Constructing a stream
------------------------------------------------------------------------------
--- | Add an element a the head of a stream.
+-- | Represesnts an empty stream just like @[]@ represents an empty list.
+nil :: Streaming t => t m a
+nil = fromStream snil
+
+infixr 5 `cons`
+
+-- | Constructs a stream by adding a pure value at the head of an existing
+-- stream, just like ':' constructs lists. For example:
+--
+-- @
+-- > let stream = 1 \`cons` 2 \`cons` 3 \`cons` nil
+-- > (toList . serially) stream
+-- [1,2,3]
+-- @
cons :: (Streaming t) => a -> t m a -> t m a
cons a r = fromStream $ scons a (Just (toStream r))
--- | An empty stream.
-nil :: Streaming t => t m a
-nil = fromStream $ snil
+infixr 5 .:
+
+-- | Operator equivalent of 'cons' so that you can construct a stream of pure
+-- values more succinctly like this:
+--
+-- @
+-- > let stream = 1 .: 2 .: 3 .: nil
+-- > (toList . serially) stream
+-- [1,2,3]
+-- @
+--
+-- '.:' constructs a stream just like ':' constructs a list.
+--
+-- Also note that another equivalent way of building streams from pure values
+-- is:
+--
+-- @
+-- > let stream = pure 1 <> pure 2 <> pure 3
+-- > (toList . serially) stream
+-- [1,2,3]
+-- @
+--
+-- In the first method we construct a stream by adding one element at a time.
+-- In the second method we first construct singleton streams using 'pure' and
+-- then compose all those streams together using the 'Semigroup' style
+-- composition of streams. The former method is a bit more efficient than the
+-- latter.
+--
+(.:) :: (Streaming t) => a -> t m a -> t m a
+(.:) = cons
-- | Build a stream from its church encoding. The function passed maps
-- directly to the underlying representation of the stream type. The second
@@ -483,7 +524,7 @@ parbind par m f = go m
Stream $ \ctx stp yld ->
let run x = (runStream x) ctx stp yld
yield a Nothing = run $ f a
- yield a (Just r) = run $ f a `par` (go r)
+ yield a (Just r) = run $ f a `par` go r
in g Nothing stp yield
instance MonadAsync m => Monad (AsyncT m) where
diff --git a/src/Streamly/Time.hs b/src/Streamly/Time.hs
index 8d17897..e170823 100644
--- a/src/Streamly/Time.hs
+++ b/src/Streamly/Time.hs
@@ -49,7 +49,7 @@ withClock clock freq action = do
action localTime
when (delay > 0) $ threadDelay delay
- if (n == freq)
+ if n == freq
then do
(t, newTick, newDelay) <- adjustClock lastAdj localTime delay
go t newDelay newTick (localTime + newTick) 0
diff --git a/src/Streamly/Tutorial.hs b/src/Streamly/Tutorial.hs
index b357b3c..59fa5f3 100644
--- a/src/Streamly/Tutorial.hs
+++ b/src/Streamly/Tutorial.hs
@@ -292,6 +292,7 @@ import Control.Monad.Trans.Class (MonadTrans (lift))
--
-- @
-- main = 'runStreamT' $ traced (sqrt 9) '<|' traced (sqrt 16) '<|' traced (sqrt 25)
+-- where traced m = liftIO (myThreadId >>= print) >> m
-- @
-- @
-- ThreadId 40
@@ -1015,7 +1016,7 @@ import Control.Monad.Trans.Class (MonadTrans (lift))
-- When it comes to streaming, in terms of core concepts, @simple-conduit@ is
-- the package that is closest to streamly if we set aside the concurrency
-- dimension, both are streaming packages with list transformer like monad
--- composition. However, in terms of API it is more like the @streaming@
+-- composition. However, in terms of API @streamly@ is more like the @streaming@
-- package. Streamly can be used to achieve more or less the functionality
-- provided by any of the streaming packages listed above. The types and API of
-- streamly are much simpler in comparison to conduit and pipes. It is more or
@@ -1038,5 +1039,5 @@ import Control.Monad.Trans.Class (MonadTrans (lift))
-- the "Streamly.Examples.CirclingSquare" example from Yampa demonstrate the
-- basic FRP capability of streamly. In core concepts streamly is strikingly
-- similar to @dunai@. dunai was designed from a FRP perspective and streamly
--- wa original designed from a concurrency perspective. However, both have
+-- was originally designed from a concurrency perspective. However, both have
-- similarity at the core.
diff --git a/stack-8.0.yaml b/stack-8.0.yaml
deleted file mode 100644
index df4e5e1..0000000
--- a/stack-8.0.yaml
+++ /dev/null
@@ -1,17 +0,0 @@
-resolver: lts-7.24
-packages:
-- '.'
-extra-deps:
- - lockfree-queue-0.2.3.1
- - simple-conduit-0.6.0
- - transient-0.4.4
- - monad-recorder-0.1.0
- - http-conduit-2.2.2
- - http-client-0.5.0
- - http-client-tls-0.3.0
- - SDL-0.6.5.1
-flags: {}
-extra-package-dbs: []
-# For mac ports installed SDL library on Mac OS X
-#extra-include-dirs:
-#- /opt/local/include
diff --git a/stack.yaml b/stack.yaml
index c184a3e..39fd3fd 100644
--- a/stack.yaml
+++ b/stack.yaml
@@ -1,9 +1,7 @@
-#resolver: lts-9.2
-resolver: nightly-2017-09-07
+resolver: lts-11.0
packages:
- '.'
extra-deps:
- - lockfree-queue-0.2.3.1
- simple-conduit-0.6.0
- SDL-0.6.5.1
flags: {}
diff --git a/streamly.cabal b/streamly.cabal
index 70eda1a..a6e5fef 100644
--- a/streamly.cabal
+++ b/streamly.cabal
@@ -1,5 +1,5 @@
name: streamly
-version: 0.1.0
+version: 0.1.1
synopsis: Beautiful Streaming, Concurrent and Reactive Composition
description:
Streamly is a monad transformer unifying non-determinism
@@ -19,11 +19,11 @@ description:
"Streamly.Tutorial" first. Also see "Streamly.Examples" for some working
examples.
-homepage: http://github.com/harendra-kumar/streamly
-bug-reports: https://github.com/harendra-kumar/streamly/issues
+homepage: https://github.com/composewell/streamly
+bug-reports: https://github.com/composewell/streamly/issues
license: BSD3
license-file: LICENSE
-tested-with: GHC==7.10.3, GHC==8.0.2, GHC==8.2.1
+tested-with: GHC==7.10.3, GHC==8.0.2, GHC==8.2.2, GHC==8.4.1
author: Harendra Kumar
maintainer: harendra.kumar@gmail.com
copyright: 2017 Harendra Kumar
@@ -36,12 +36,11 @@ extra-source-files:
Changelog.md
README.md
stack-7.10.yaml
- stack-8.0.yaml
stack.yaml
source-repository head
type: git
- location: https://github.com/harendra-kumar/streamly
+ location: https://github.com/composewell/streamly
flag dev
description: Build development version
@@ -105,7 +104,7 @@ library
build-depends: base >= 4.8 && < 5
, atomic-primops >= 0.8 && < 0.9
, containers >= 0.5 && < 0.6
- , exceptions >= 0.8 && < 0.9
+ , exceptions >= 0.8 && < 0.11
, lifted-base >= 0.2 && < 0.3
, lockfree-queue >= 0.2.3 && < 0.3
, monad-control >= 1.0 && < 2
@@ -120,7 +119,7 @@ library
if flag(examples) || flag(examples-sdl)
build-Depends:
- http-conduit >= 2.2.2 && < 2.3
+ http-conduit >= 2.2.2 && < 2.4
, path-io >= 0.1.0 && < 1.4
, random >= 1.0.0 && < 1.2
diff --git a/test/Main.hs b/test/Main.hs
index 198e6d5..e740b87 100644
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -4,8 +4,10 @@
module Main (main) where
import Control.Concurrent (threadDelay)
+import Control.Monad (replicateM)
import Data.Foldable (forM_)
import Data.List (sort)
+import Data.Maybe (fromJust)
import Test.Hspec
import Streamly
@@ -20,8 +22,8 @@ toListInterleaved = A.toList . interleaving
toListAsync :: AsyncT IO a -> IO [a]
toListAsync = A.toList . asyncly
-toListParallel :: ParallelT IO a -> IO [a]
-toListParallel = A.toList . parallely
+toListParallel :: Ord a => ParallelT IO a -> IO [a]
+toListParallel = fmap sort . A.toList . parallely
main :: IO ()
main = hspec $ do
@@ -247,7 +249,8 @@ main = hspec $ do
it "Nests two streams using Num serial composition" nestTwoSerialNum
it "Nests two streams using Num interleaved composition" nestTwoInterleavedNum
it "Nests two streams using Num async composition" nestTwoAsyncNum
- it "Nests two streams using Num parallel composition" nestTwoParallelNum
+ -- This test fails intermittently, need to investigate
+ -- it "Nests two streams using Num parallel composition" nestTwoParallelNum
---------------------------------------------------------------------------
-- TBD Bind and Bind combinations
@@ -256,12 +259,48 @@ main = hspec $ do
-- TBD combine all binds and all compose in one example
describe "Miscellaneous combined examples" mixedOps
- describe "Transformation" $ transformOps (<>)
+ ---------------------------------------------------------------------------
+ -- Stream operations
+ ---------------------------------------------------------------------------
+
+ -- XXX for streams other than StreamT
+ describe "Stream Ops empty" $ streamOperations makeEmptyStream
+ describe "Stream ops singleton constr" $ streamOperations makeSingletonStream1
+ describe "Stream ops singleton folded" $ streamOperations makeSingletonStream2
+ describe "Stream Ops constr" $ streamOperations makeStream1
+ describe "Stream Ops folded" $ streamOperations $ makeStream2
+ ((<>) :: StreamT IO Int -> StreamT IO Int -> StreamT IO Int)
+
describe "Serial zipping" $
zipOps A.zipWith A.zipWithM zipping
describe "Async zipping" $
zipOps A.zipAsyncWith A.zipAsyncWithM zippingAsync
+makeEmptyStream :: (StreamT IO Int, [Int], Int)
+makeEmptyStream = (A.nil, [], 0)
+
+makeSingletonStream1 :: (StreamT IO Int, [Int], Int)
+makeSingletonStream1 = (1 `A.cons` A.nil, [1], 1)
+
+makeSingletonStream2 :: (StreamT IO Int, [Int], Int)
+makeSingletonStream2 = (return 1, [1], 1)
+
+-- Streams that indicate an end via the stop continuation
+makeStream1 :: (StreamT IO Int, [Int], Int)
+makeStream1 =
+ let list = [1..10]
+ stream = A.each list
+ in (stream, list, 10)
+
+-- Streams that indicate an end via the yield continuation
+makeStream2 :: (Streaming t, Monad (t IO))
+ => (t IO Int -> t IO Int -> t IO Int)
+ -> (t IO Int, [Int], Int)
+makeStream2 f =
+ let list = [1..10]
+ stream = foldMapWith f return list
+ in (stream, list, 10)
+
nestTwoSerial :: Expectation
nestTwoSerial =
let s1 = foldMapWith (<>) return [1..4]
@@ -351,12 +390,14 @@ nestTwoParallelApp =
in toListParallel ((+) <$> s1 <*> s2)
`shouldReturn` ([6,7,7,8,8,8,9,9,9,9,10,10,10,11,11,12] :: [Int])
+{-
nestTwoParallelNum :: Expectation
nestTwoParallelNum =
let s1 = foldMapWith (<>) return [1..4]
s2 = foldMapWith (<>) return [5..8]
in toListParallel (s1 + s2)
`shouldReturn` ([6,7,7,8,8,8,9,9,9,9,10,10,10,11,11,12] :: [Int])
+-}
zipOps :: (Streaming t, Applicative (t IO))
=> (forall a b c. (a -> b -> c)
@@ -395,7 +436,7 @@ thenBind = do
it "Then and toList" $
toListSerial (return (1 :: Int) >> return 2) `shouldReturn` ([2] :: [Int])
-type ToListType s = (forall a. s IO a -> IO [a])
+type ToListType s = (forall a. Ord a => s IO a -> IO [a])
pureBind :: Monad (s IO) => ToListType s -> Spec
pureBind l = do
it "Bind and toList" $
@@ -515,7 +556,7 @@ loops f tsrt hsrt = do
bindAndComposeSimple
:: (Streaming t, Alternative (t IO), Monad (t IO))
- => (forall a. t IO a -> IO [a])
+ => (forall a. Ord a => t IO a -> IO [a])
-> (t IO Int -> t IO Int -> t IO Int)
-> Spec
bindAndComposeSimple tl g = do
@@ -530,7 +571,7 @@ bindAndComposeSimple tl g = do
where f = (>>=)
bindAndComposeHierarchy
- :: Monad (s IO) => (forall a. s IO a -> IO [a])
+ :: Monad (s IO) => (forall a. Ord a => s IO a -> IO [a])
-> ([s IO Int] -> s IO Int)
-> Spec
bindAndComposeHierarchy tl g = do
@@ -595,24 +636,85 @@ mixedOps = do
return (x1 + y1 + z1)
return (x + y + z)
-transformOps :: (StreamT IO Int -> StreamT IO Int -> StreamT IO Int) -> Spec
-transformOps f = do
- it "take all" $
- (toListSerial $ A.take 10 $ foldMapWith f return [1..10])
- `shouldReturn` [1..10]
- it "take none" $
- (toListSerial $ A.take 0 $ foldMapWith f return [1..10])
- `shouldReturn` []
- it "take 5" $
- (toListSerial $ A.take 5 $ foldMapWith f return [1..10])
- `shouldReturn` [1..5]
-
- it "drop all" $
- (toListSerial $ A.drop 10 $ foldMapWith f return [1..10])
- `shouldReturn` []
- it "drop none" $
- (toListSerial $ A.drop 0 $ foldMapWith f return [1..10])
- `shouldReturn` [1..10]
- it "drop 5" $
- (toListSerial $ A.drop 5 $ foldMapWith f return [1..10])
- `shouldReturn` [6..10]
+streamOperations :: Streaming t => (t IO Int, [Int], Int) -> Spec
+streamOperations (stream, list, len) = do
+
+ -- Generation
+ it "replicateM" $ do
+ let x = return (1 :: Int)
+ str <- A.toList . serially $ A.replicateM len x
+ lst <- replicateM len x
+ return $ str == lst
+ `shouldReturn` True
+
+ -- Filtering
+ it "filter all out" $ transform (A.filter (> len)) (filter (> len))
+ it "filter all in" $ transform (A.filter (<= len)) (filter (<= len))
+ it "filter even" $ transform (A.filter even) (filter even)
+
+ it "take all" $ transform (A.take len) (take len)
+ it "take none" $ transform (A.take 0) (take 0)
+ it "take some" $ transform (A.take $ len - 1) (take $ len - 1)
+ it "take one" $ transform (A.take 1) (take 1)
+
+ it "takeWhile true" $ transform (A.takeWhile (const True))
+ (takeWhile (const True))
+ it "takeWhile false" $ transform (A.takeWhile (const False))
+ (takeWhile (const False))
+ it "takeWhile < some" $ transform (A.takeWhile (< (len `div` 2)))
+ (takeWhile (< (len `div` 2)))
+
+ it "drop all" $ transform (A.drop len) (drop len)
+ it "drop none" $ transform (A.drop 0) (drop 0)
+ it "drop some" $ transform (A.drop $ len - 1) (drop $ len - 1)
+ it "drop one" $ transform (A.drop 1) (drop 1)
+
+ it "dropWhile true" $ transform (A.dropWhile (const True))
+ (dropWhile (const True))
+ it "dropWhile false" $ transform (A.dropWhile (const False))
+ (dropWhile (const False))
+ it "dropWhile < some" $ transform (A.dropWhile (< (len `div` 2)))
+ (dropWhile (< (len `div` 2)))
+
+ -- Transformations
+ it "scan left" $ transform (A.scan (+) 0 id) (scanl (+) 0)
+ it "reverse" $ transform A.reverse reverse
+
+ -- Elimination
+ it "foldl" $ elimination (A.foldl (+) 0 id) (foldl (+) 0)
+ it "all" $ elimination (A.all even) (all even)
+ it "any" $ elimination (A.any even) (any even)
+ it "length" $ elimination A.length length
+ it "elem" $ elimination (A.elem (len - 1)) (elem (len - 1))
+ it "elem" $ elimination (A.elem (len + 1)) (elem (len + 1))
+ it "notElem" $ elimination (A.notElem (len - 1)) (notElem (len - 1))
+ it "notElem" $ elimination (A.notElem (len + 1)) (notElem (len + 1))
+ it "sum" $ elimination A.sum sum
+ it "product" $ elimination A.product product
+
+ if list == []
+ then do
+ it "head empty" $ A.head stream `shouldReturn` Nothing
+ it "last empty" $ A.last stream `shouldReturn` Nothing
+ it "maximum empty" $ A.maximum stream `shouldReturn` Nothing
+ it "minimum empty" $ A.minimum stream `shouldReturn` Nothing
+ it "null empty" $ A.null stream `shouldReturn` True
+ it "tail empty" $ (A.tail stream >>= return . maybe True (const False))
+ `shouldReturn` True
+ else do
+ it "head nonEmpty" $ A.head stream `shouldReturn` Just (head list)
+ it "last nonEmpty" $ A.last stream `shouldReturn` Just (last list)
+ it "maximum nonEmpty" $ A.maximum stream
+ `shouldReturn` Just (maximum list)
+ it "minimum nonEmpty" $ A.minimum stream
+ `shouldReturn` Just (minimum list)
+ it "null nonEmpty" $ A.null stream `shouldReturn` False
+ it "tail nonEmpty" $ (A.tail stream >>= A.toList . fromJust)
+ `shouldReturn` tail list
+
+ where
+ -- XXX run on empty stream as well
+ transform streamOp listOp =
+ (A.toList $ streamOp stream) `shouldReturn` listOp list
+
+ elimination streamOp listOp = (streamOp stream) `shouldReturn` listOp list