streamly/Changelog.md

Unreleased

Breaking changes

• Change the signature of foldrM to ensure that it is lazy
• Change the signature of iterateM to ensure that it is lazy.
• scanx would now require an additional Monad m constraint.

Behavior change

• Earlier ParallelT was unaffected by maxBuffer directive, now maxBuffer can limit the buffer of a ParallelT stream as well. When the buffer becomes full, the producer threads block.
• ParallelT streams no longer have an unlimited buffer by default. Now the buffer for parallel streams is limited to 1500 by default, the same as other concurrent stream types.

Deprecations

• In Streamly.Prelude:

  • runStream has been replaced by drain
  • runN has been replaced by drainN
  • runWhile has been replaced by drainWhile
  • fromHandle has been deprecated. Please use Streamly.FileSystem.Handle.read, Streamly.String.decodeUtf8 and Streamly.String.lines to split the stream into lines. Use Streamly.String.foldLine with Streamly.Fold.toList if you want to convert the stream to a stream of String.
  • toHandle has been deprecated. Please use intersperse and concat to add newlines to a stream, Streamly.String.encodeUtf8 for encoding and Streamly.FileSystem.Handle.write for writing to a file handle.
  • Deprecate scanx, foldx, foldxM, foldr1
  • Remove deprecated APIs scan, foldl, foldlM

• In Streamly module:

  • runStream has been deprecated, please use Streamly.Prelude.drain
  • foldWith, foldMapWith, forEachWith have been moved to Streamly.Prelude module.

Bug Fixes

• Fix a bug that caused uniq function to yield the same element twice.

Major Enhancements

This release contains a lot of new features and major enhancements. For more details on the new features described below please see the haddock docs of the modules on hackage.

Exception Handling

See Streamly.Prelude for new exception handling combinators like before, after, bracket, onException, finally, handle etc.

Composable Folds

Streamly.Fold module provides composable folds (stream consumers). Folds allow splitting, grouping, partitioning, unzipping and nesting a stream onto multiple folds without breaking the stream. Combinators are provided for temporal and spatial window based fold operations, for example, to support folding and aggregating data for timeout or inactivity based sessions.

Streaming File IO

Streamly.FileSystem.Handle provides handle based streaming file IO operations.

Streaming Network IO

Streamly.Network.Socket provides socket based streaming network IO operations.

Concurrent concatMap

The new concatMapWith combinator performs a concatMap using a supplied merge/concat strategy. This is a very powerful combinator as you can, for example, concat streams concurrently using this.

Other Enhancements

• Add the following new features/modules:

  • Unicode Strings: Streamly.String module provides encoding/decoding of character streams and other character stream operations.
  • Arrays: Streamly.Memory.Array module provides arrays for efficient in-memory buffering and efficient interfacing with IO.
  • Streamly.Memory.ArrayStream module provide combinators to work on streams of arrays.

• Add the following to Streamly.Prelude:

  • runFold, runScan and runPostscan
  • intervalsOf and chunksOf
  • splitOn, splitOnSuffix, splitWithSuffix, and wordsBy
  • groups, groupsBy and groupsByRolling
  • postscanl' and postscanlM'
  • intersperse intersperse an element in between consecutive elements in stream
  • trace combinator maps a monadic function on a stream just for side effects
  • tap redirects a copy of the stream to a Fold

0.6.1

Bug Fixes

• Fix a bug that caused maxThreads directive to be ignored when rate control was not used.

Enhancements

• Add GHCJS support
• Remove dependency on "clock" package

0.6.0

Breaking changes

• Monad constraint may be needed on some of the existing APIs (findIndices and elemIndices).

Enhancements

• Add the following functions to Streamly.Prelude:
  • Generation: replicate, fromIndices, fromIndicesM
  • Enumeration: Enumerable type class, enumerateFrom, enumerateFromTo, enumerateFromThen, enumerateFromThenTo, enumerate, enumerateTo
  • Running: runN, runWhile
  • Folds: (!!), maximumBy, minimumBy, the
  • Scans: scanl1', `scanl1M'
  • Filters: uniq, insertBy, deleteBy, findM
  • Multi-stream: eqBy, cmpBy, mergeBy, mergeByM, mergeAsyncBy, mergeAsyncByM, isPrefixOf, isSubsequenceOf, stripPrefix, concatMap, concatMapM, indexed, indexedR
• Following instances were added for SerialT m, WSerialT m and ZipSerialM m:
  • When m ~ Identity: IsList, Eq, Ord, Show, Read, IsString, NFData, NFData1, Traversable
  • When m is Foldable: Foldable
• Performance improvements
• Add benchmarks to measure composed and iterated operations

0.5.2

Bug Fixes

• Cleanup any pending threads when an exception occurs.
• Fixed a livelock in ahead style streams. The problem manifests sometimes when multiple streams are merged together in ahead style and one of them is a nil stream.
• As per expected concurrency semantics each forked concurrent task must run with the monadic state captured at the fork point. This release fixes a bug, which, in some cases caused an incorrect monadic state to be used for a concurrent action, leading to unexpected behavior when concurrent streams are used in a stateful monad e.g. StateT. Particularly, this bug cannot affect ReaderT.

0.5.1

• Performance improvements, especially space consumption, for concurrent streams

0.5.0

Bug Fixes

• Leftover threads are now cleaned up as soon as the consumer is garbage collected.
• Fix a bug in concurrent function application that in certain cases would unnecessarily share the concurrency state resulting in incorrect output stream.
• Fix passing of state across parallel, async, wAsync, ahead, serial, wSerial combinators. Without this fix combinators that rely on state passing e.g. maxThreads and maxBuffer won't work across these combinators.

Enhancements

• Added rate limiting combinators rate, avgRate, minRate, maxRate and constRate to control the yield rate of a stream.
• Add foldl1', foldr1, intersperseM, find, lookup, and, or, findIndices, findIndex, elemIndices, elemIndex, init to Prelude

Deprecations

• The Streamly.Time module is now deprecated, its functionality is subsumed by the new rate limiting combinators.

0.4.1

Bug Fixes

• foldxM was not fully strict, fixed.

0.4.0

Breaking changes

• Signatures of zipWithM and zipAsyncWithM have changed
• Some functions in prelude now require an additional Monad constraint on the underlying type of the stream.

Deprecations

• once has been deprecated and renamed to yieldM

Enhancements

• Add concurrency control primitives maxThreads and maxBuffer.
• Concurrency of a stream with bounded concurrency when used with take is now limited by the number of elements demanded by take.
• Significant performance improvements utilizing stream fusion optimizations.
• Add yield to construct a singleton stream from a pure value
• Add repeat to generate an infinite stream by repeating a pure value
• Add fromList and fromListM to generate streams from lists, faster than fromFoldable and fromFoldableM
• Add map as a synonym of fmap
• Add scanlM', the monadic version of scanl'
• Add takeWhileM and dropWhileM
• Add filterM

0.3.0

Breaking changes

• Some prelude functions, to whom concurrency capability has been added, will now require a MonadAsync constraint.

Bug Fixes

• Fixed a race due to which, in a rare case, we might block indefinitely on an MVar due to a lost wakeup.
• Fixed an issue in adaptive concurrency. The issue caused us to stop creating more worker threads in some cases due to a race. This bug would not cause any functional issue but may reduce concurrency in some cases.

Enhancements

• Added a concurrent lookahead stream type Ahead
• Added fromFoldableM API that creates a stream from a container of monadic actions
• Monadic stream generation functions consM, |:, unfoldrM, replicateM, repeatM, iterateM and fromFoldableM can now generate streams concurrently when used with concurrent stream types.
• Monad transformation functions mapM and sequence can now map actions concurrently when used at appropriate stream types.
• Added concurrent function application operators to run stages of a stream processing function application pipeline concurrently.
• Added mapMaybe and mapMaybeM.

0.2.1

Bug Fixes

• Fixed a bug that caused some transformation ops to return incorrect results when used with concurrent streams. The affected ops are take, filter, takeWhile, drop, dropWhile, and reverse.

0.2.0

Breaking changes

• Changed the semantics of the Semigroup instance for InterleavedT, AsyncT and ParallelT. The new semantics are as follows:

  • For InterleavedT, <> operation interleaves two streams
  • For AsyncT, <> now concurrently merges two streams in a left biased manner using demand based concurrency.
  • For ParallelT, the <> operation now concurrently meges the two streams in a fairly parallel manner.

  To adapt to the new changes, replace <> with serial wherever it is used for stream types other than StreamT.

• Remove the Alternative instance. To adapt to this change replace any usage of <|> with parallel and empty with nil.

• Stream type now defaults to the SerialT type unless explicitly specified using a type combinator or a monomorphic type. This change reduces puzzling type errors for beginners. It includes the following two changes:

  • Change the type of all stream elimination functions to use SerialT instead of a polymorphic type. This makes sure that the stream type is always fixed at all exits.
  • Change the type combinators (e.g. parallely) to only fix the argument stream type and the output stream type remains polymorphic.

  Stream types may have to be changed or type combinators may have to be added or removed to adapt to this change.

• Change the type of foldrM to make it consistent with foldrM in base.

• async is renamed to mkAsync and async is now a new API with a different meaning.

• ZipAsync is renamed to ZipAsyncM and ZipAsync is now ZipAsyncM specialized to the IO Monad.

• Remove the MonadError instance as it was not working correctly for parallel compositions. Use MonadThrow instead for error propagation.

• Remove Num/Fractional/Floating instances as they are not very useful. Use fmap and liftA2 instead.

Deprecations

• Deprecate and rename the following symbols:
  • Streaming to IsStream
  • runStreaming to runStream
  • StreamT to SerialT
  • InterleavedT to WSerialT
  • ZipStream to ZipSerialM
  • ZipAsync to ZipAsyncM
  • interleaving to wSerially
  • zipping to zipSerially
  • zippingAsync to zipAsyncly
  • <=> to wSerial
  • <| to async
  • each to fromFoldable
  • scan to scanx
  • foldl to foldx
  • foldlM to foldxM
• Deprecate the following symbols for future removal:
  • runStreamT
  • runInterleavedT
  • runAsyncT
  • runParallelT
  • runZipStream
  • runZipAsync

Enhancements

• Add the following functions:
  • consM and |: operator to construct streams from monadic actions
  • once to create a singleton stream from a monadic action
  • repeatM to construct a stream by repeating a monadic action
  • scanl' strict left scan
  • foldl' strict left fold
  • foldlM' strict left fold with a monadic fold function
  • serial run two streams serially one after the other
  • async run two streams asynchronously
  • parallel run two streams in parallel (replaces <|>)
  • WAsyncT stream type for BFS version of AsyncT composition
• Add simpler stream types that are specialized to the IO monad
• Put a bound (1500) on the output buffer used for asynchronous tasks
• Put a limit (1500) on the number of threads used for Async and WAsync types

0.1.2

Enhancements

• Add iterate, iterateM stream operations

Bug Fixes

• Fixed a bug that casued unexpected behavior when pure was used to inject values in Applicative composition of ZipStream and ZipAsync types.

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