Changelog.md

# Changelog

## 0.10.0 (Nov 2023)

See
[0.9.0-0.10.0 API Changelog](https://github.com/composewell/streamly/blob/streamly-0.10.0/docs/User/Project/ApiChangelogs/0.9.0-0.10.0.txt)
for a full list of API changes in this release. Only a few significant
changes are mentioned here. For changes to the core functionality
please see the changelog of the `streamly-core` package.

### Breaking Changes

* `MonadTrans` and `MonadBase` instances have been removed for `AsyncT`,
`ParallelT`, `AheadT` for GHC versions 9.6 onwards. This is due to a
breaking change in `transformers` 0.6. You can replace `lift` with
`fromEffect` when using these as top level monads in a monad stack.

### Enhancements

* __Concurrent Folds__: `Streamly.Data.Fold.Prelude` module added with
concurrent fold APIs and a container fold API to fold a key value
stream to a HashMap.

## 0.9.0 (Mar 2023)

Also see the following:

* [streamly-0.9.0 Upgrade Guide](https://github.com/composewell/streamly/blob/streamly-0.10.0/docs/User/Project/Upgrading-0.8-to-0.9.md) or
https://hackage.haskell.org/package/streamly-0.9.0/docs/docs/User/ProjectRelated/Upgrading.md
* [streamly-0.9.0 API Changelog](https://github.com/composewell/streamly/blob/streamly-0.10.0/docs/User/Project/ApiChangelogs/0.8.3-0.9.0.txt) or
https://hackage.haskell.org/package/streamly-0.9.0/docs/docs/User/ProjectRelated/ApiChangelogs/0.8.3-0.9.0.txt
* [streamly-core-0.1.0 API Changelog](https://github.com/composewell/streamly/blob/streamly-0.10.0/core/docs/ApiChangelogs/0.1.0.txt) or
https://hackage.haskell.org/package/streamly-core-0.1.0/docs/docs/ApiChangelogs/0.1.0.txt

### Package split

`streamly` package is split into two packages, (1) `streamly-core` that
has only GHC boot library depdendecies, and (2) `streamly` that contains
higher level operations (including concurrent ones) with additional
dependencies. Make sure you add a dependency on `streamly-core` to keep old
code working.

* Moved the following modules from `streamly` package to the
`streamly-core` package:
* Streamly.Console.Stdio
* Streamly.Data.Fold
* Streamly.Data.Unfold
* Streamly.FileSystem.Handle
* Streamly.Unicode.Stream

### Breaking Changes

* Unboxed arrays now require `Unbox` constraint instead of `Storable`.
The `Unbox` typeclass can be imported from `Streamly.Data.Array`. You
can use generic deriving to derive Unbox instances.
* Stream type in all modules has been changed to the new `Stream` type
replacing the existing `IsStream t` or `SerialT` types. Use `fromStream`,
`toStream` from `Streamly.Prelude` module to adapt the types.
* Signatures changed in `Streamly.Data.Unfold`:
* `fromStream`
* `replicateM`

### Major Changes

`Streamly.Prelude` module has been deprecated, equivalent
functionality is covered by the `Streamly.Data.Stream`,
`Streamly.Data.Stream.Prelude`, and `Streamly.Data.Fold` modules. The
new modules use a monomorphic `Stream` type instead of the polymorphic
`IsStream t` type.

`Streamly.Data.Stream` module and the `Stream` type are meant for
writing high-performance fused pipelines not involving explicit
recursion. For writing code that may require recursive function calls,
`Streamly.Data.Stream.StreamK` module and the `StreamK` type have been
added which provide a CPS based stream implementation. `Stream` and
`StreamK` types can be easily interconverted.

The old code can be adapted to use the new modules with some changes.
See the
[streamly-0.9.0 Upgrade Guide](https://github.com/composewell/streamly/blob/streamly-0.10.0/docs/User/Project/Upgrading-0.8-to-0.9.md)
for more details on how to adapt your existing code to the new release.

### Enhancements

* Added the following new modules to the `streamly` package:
* Streamly.Data.Stream.MkType
* Streamly.Data.Stream.Prelude
* Added the following new modules to the `streamly-core` package:
* Streamly.Data.Array
* Streamly.Data.Array.Generic
* Streamly.Data.MutArray
* Streamly.Data.MutArray.Generic
* Streamly.Data.Parser
* Streamly.Data.ParserK
* Streamly.Data.Stream
* Streamly.Data.StreamK
* Streamly.FileSystem.Dir
* Streamly.FileSystem.File
* Streamly.Unicode.Parser
* Streamly.Unicode.String

### Deprecations

* Remove support for GHC 8.4.*

Several modules and functions have been deprecated, equivalent modules or
functions are suggested in the deprecation warning messages by the compiler.

### Internal module changes

If you cannot find an internal module that you were using, it may have
been moved to the `streamly-core` package or may have been renamed.

Following modules are moved to `streamly-core` package and renamed:
* Streamly.Internal.Data.Array.Stream.Foreign -> Streamly.Internal.Data.Stream.Chunked
* Streamly.Internal.Data.Array.Stream.Mut.Foreign -> Streamly.Internal.Data.Array.Mut.Stream

## 0.8.3 (September 2022)

* Fix build with GHC 9.4

## 0.8.2 (Mar 2022)

* Fix performance issues for GHC-9. These changes coupled with GHC changes
expected to land in 9.2.2 will bring the performance back to the same levels
as before.

## 0.8.1.1 (Dec 2021)

* Disable building FileSystem.Events where FS Events isn't supported.

## 0.8.1 (Nov 2021)

See ApiChangelogs/0.8.3.txt for new APIs introduced.

### Bug Fixes

* Several bug fixes in the Array module:
* Fix writeN fold eating away one element when applied multiple times
[#1258](https://github.com/composewell/streamly/issues/1258).
* Fix potentially writing beyond allocated memory when shrinking. Likely
cause of [#944](https://github.com/composewell/streamly/issues/944).
* Fix potentially writing beyond allocated memory when writing the last
element. Likely cause of
[#944](https://github.com/composewell/streamly/issues/944).
* Fix missing pointer touch could potentially cause use of freed memory.
* Fix unnecessary additional allocation due to a bug
* Fix a bug in classifySessionsBy, see
[PR #1311](https://github.com/composewell/streamly/pull/1311). The bug
could cause premature ejection of a session when input events with the
same key are split into multiple sessions.

### Notable Internal API Changes

* `tapAsync` from `Streamly.Internal.Data.Stream.Parallel` has been moved to
`Streamly.Internal.Data.Stream.IsStream` and renamed to `tapAsyncK`.
* `Fold2` has now been renamed to `Refold` and the corresponding `Fold2`
combinators have been either renamed or removed.

## 0.8.0 (Jun 2021)

See [API Changelog](/docs/User/Project/ApiChangelogs/0.8.3.txt) for a complete list of signature
changes and new APIs introduced.

### Breaking changes

* `Streamly.Prelude`
* `fold`: this function may now terminate early without consuming
the entire stream. For example, `fold Fold.head stream` would
now terminate immediately after consuming the head element from
`stream`. This may result in change of behavior in existing programs
if the program relies on the evaluation of the full stream.
* `Streamly.Data.Unicode.Stream`
* The following APIs no longer throw errors on invalid input, use new
APIs suffixed with a prime for strict behavior:
* decodeUtf8
* encodeLatin1
* encodeUtf8
* `Streamly.Data.Fold`:
* Several instances have been moved to the `Streamly.Data.Fold.Tee`
module, please use the `Tee` type to adapt to the changes.

### Bug Fixes

* Concurrent Streams: The monadic state for the stream is now propagated across
threads. Please refer to
[#369](https://github.com/composewell/streamly/issues/369) for more info.
* `Streamly.Prelude`:
* `bracket`, `handle`, and `finally` now also work correctly on streams
that aren't fully drained. Also, the resource acquisition and release is
atomic with respect to async exceptions.
* `iterate`, `iterateM` now consume O(1) space instead of O(n).
* `fromFoldableM` is fixed to be concurrent.
* `Streamly.Network.Inet.TCP`: `accept` and `connect` APIs now close the socket
if an exception is thrown.
* `Streamly.Network.Socket`: `accept` now closes the socket if an exception is
thrown.

### Enhancements

* See [API Changelog](/docs/User/Project/ApiChangelogs/0.8.3.txt) for a complete list of new
modules and APIs introduced.
* The Fold type is now more powerful, the new termination behavior allows
to express basic parsing of streams using folds.
* Many new Fold and Unfold APIs are added.
* A new module for console IO APIs is added.
* Experimental modules for the following are added:
* Parsing
* Deserialization
* File system event handling (fsnotify/inotify)
* Folds for streams of arrays
* Experimental `use-c-malloc` build flag to use the c library `malloc` for
array allocations. This could be useful to avoid pinned memory fragmentation.

### Notable Internal/Pre-release API Changes

Breaking changes:

* The `Fold` type has changed to accommodate terminating folds.
* Rename: `Streamly.Internal.Prelude` => `Streamly.Internal.Data.Stream.IsStream`
* Several other internal modules have been renamed and re-factored.

Bug fixes:

* A bug was fixed in the conversion of `MicroSecond64` and `MilliSecond64`
(commit e5119626)
* Bug fix: `classifySessionsBy` now flushes sessions at the end and terminates.

### Miscellaneous

* Drop support for GHC 7.10.3.
* The examples in this package are moved to a new github repo
[streamly-examples](https://github.com/composewell/streamly-examples)

## 0.7.3 (February 2021)

### Build Issues

* Fix build issues with primitive package version >= 0.7.1.
* Fix build issues on armv7.

## 0.7.2 (April 2020)

### Bug Fixes

* Fix a bug in the `Applicative` and `Functor` instances of the `Fold`
data type.

### Build Issues

* Fix a bug that occasionally caused a build failure on windows when
used with `stack` or `stack ghci`.
* Now builds on 32-bit machines.
* Now builds with `primitive` package version >= 0.5.4 && <= 0.6.4.0
* Now builds with newer `QuickCheck` package version >= 2.14 && < 2.15.
* Now builds with GHC 8.10.

## 0.7.1 (February 2020)

### Bug Fixes

* Fix a bug that caused `findIndices` to return wrong indices in some
cases.
* Fix a bug in `tap`, `chunksOf` that caused memory consumption to
increase in some cases.
* Fix a space leak in concurrent streams (`async`, `wAsync`, and `ahead`) that
caused memory consumption to increase with the number of elements in the
stream, especially when built with `-threaded` and used with `-N` RTS option.
The issue occurs only in cases when a worker thread happens to be used
continuously for a long time.
* Fix scheduling of WAsyncT stream style to be in round-robin fashion.
* Now builds with `containers` package version < 0.5.8.
* Now builds with `network` package version >= 3.0.0.0 && < 3.1.0.0.

### Behavior change

* Combinators in `Streamly.Network.Inet.TCP` no longer use TCP `NoDelay` and
`ReuseAddr` socket options by default. These options can now be specified
using appropriate combinators.

### Performance

* Now uses `fusion-plugin` package for predictable stream fusion optimizations
* Significant improvement in performance of concurrent stream operations.
* Improved space and time performance of `Foldable` instance.

## 0.7.0 (November 2019)

### 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.Data.Unicode.Stream.decodeUtf8` and
`splitOnSuffix` with `Streamly.Data.Fold.toList` to split the
stream to a stream of `String` separated by a newline.
* `toHandle` has been deprecated. Please use `intersperse` and `concatUnfold` to
add newlines to a stream, `Streamly.Data.Unicode.Stream.encodeUtf8` for encoding and
`Streamly.FileSystem.Handle.write` for writing to a file handle.
* Deprecate `scanx`, `foldx`, `foldxM`, `foldr1`
* Remove deprecated APIs `foldl`, `foldlM`
* Replace deprecated API `scan` with a new signature, to scan using Fold.

* In `Streamly` module:
* `runStream` has been deprecated, please use `Streamly.Prelude.drain`

* Remove deprecated module `Streamly.Time` (moved to Streamly.Internal.Data.Time)
* Remove module `Streamly.Internal` (functionality moved to the Internal hierarchy)

### Bug Fixes

* Fix a bug that caused `uniq` function to yield the same element twice.
* Fix a bug that caused "thread blocked indefinitely in an MVar operation"
exception in a parallel stream.
* Fix unbounded memory usage (leak) in `parallel` combinator. The bug manifests
when large streams are combined using `parallel`.

### 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.Data.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.

#### Composable Unfolds

`Streamly.Data.Unfold` module provides composable stream generators. Unfolds allow
high performance merging/flattening/combining of stream generators.

#### 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.

* `Streamly.Network.Inet.TCP` provides combinators to build Inet/TCP
clients and servers.

#### Concurrent concatMap

The new `concatMapWith` in `Streamly.Prelude` 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.Data.Unicode.Stream` 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.

* Add the following to `Streamly.Prelude`:
* `unfold`, `fold`, `scan` and `postscan`
* `concatUnfold` to concat a stream after unfolding each element
* `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 (March 2019)

### 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 (December 2018)

### 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 (October 2018)

### 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 (September 2018)

* Performance improvements, especially space consumption, for concurrent
streams

## 0.5.0 (September 2018)

### 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 (July 2018)

### Bug Fixes

* foldxM was not fully strict, fixed.

## 0.4.0 (July 2018)

### 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 (June 2018)

### 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 (June 2018)

### 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 (May 2018)

### 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 (March 2018)

### Enhancements
* Add `iterate`, `iterateM` stream operations

### Bug Fixes
* Fixed a bug that caused unexpected behavior when `pure` was used to inject
values in Applicative composition of `ZipStream` and `ZipAsync` types.

## 0.1.1 (March 2018)

### 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 (December 2017)

* Initial release