Add changelog.

Author: foxik

changelog.md

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+# Changelog for [`containers` package](http://github.com/haskell/containers)
+
+## 0.5.7.1  *Dec 2015*
+
+  * Planned to bundle with GHC 8.0.1.
+
+  * Add `IsString` instance to `Data.Sequence`.
+
+  * Define `Semigroup` instances for ``Data.Map`, `Data.Set`, `Data.IntMap`,
+    `Data.IntSet` and `Data.Sequence`.
+
+## 0.5.6.2  *Dec 2014*
+
+  * Bundled with GHC 7.10.1.
+
+  * Add role annotations for `Data.Map` and `Data.Set`.
+
+  * Add `IsList` instances for `Data.Map`, `Data.Set`, `Data.IntMap` and
+    `Data.IntSet`.
+
+  * Several performance improvements for `Data.Sequence`.
+
+  * Add `Data.Sequence.fromFunction` and `Data.Sequence.fromArray`.
+
+## 0.5.4.0  *Jan 2014*
+
+  * Bundled with GHC 7.8.1.
+
+  * The `Data.Map.fromList` and `Data.Set.fromList` now use linear-time
+    algorithm if the input is sorted, without need to call `fromDistinctAscList`.
+
+  * Implement indexing operations (`lookupIndex`, `findIndex`, `elemAt`,
+    `deletaAt`) for `Data.Set` too.
+
+  * Add `Applicative` and `Alternative` instances for `Data.Sequence`.
+
+  * Add `foldMapWithKey` to `Data.Map` and `Data.IntMap`.
+
+  * Implement poly-kinded `Typeable`.
+
+  * Add `Functor` instance for `Data.Graph.SCC`.
+
+  * Add `Data.Map.splitRoot` and `Data.Set.splitRoot`.
+
+## 0.5.0.0  *May 2012*
+
+  * Bundled with GHC 7.6.1.
+
+  * Major improvements since last release:
+    * a clearer distinction between value-lazy and value-strict containers,
+    * performance improvements across the board,
+    * a big internal clean-up, and
+    * new functions for e.g. merging, updating, and searching containers.
+
+  * While the old `Data.Map` and
+    `Data.IntMap` modules will continue to exist for the foreseeable future, we've
+    abandoned the practice of having the strict and lazy versions of each
+    function distinguished by an apostrophe. The distinction is instead made at
+    the module level, by introducing four new modules:
+    * Data.Map.Strict
+    * Data.Map.Lazy
+    * Data.IntMap.Strict
+    * Data.IntMap.Lazy
+
+    This split has three benefits:
+    * It makes the choice between value-strict and value-lazy containers
+      more declarative; you pick once at import time, instead of having to
+      remember to use the strict or lazy versions of a function every time
+      you modify the container.
+    * It alleviates a common source of performance issues, by forcing the
+      user to think about the strictness properties upfront. For example,
+      using insertWith instead of insertWith' is a common source of
+      containers-related performance bugs.
+    * There are fewer functions per module, making it easier to get an
+      overview of each module.
+
+  * Note that the types used in the strict and lazy APIs are the same, so
+    you can still use the same container in a "mixed" manner, if needed.
+
+  * The `Data.IntSet` representation changed to store small sets using
+    bits in an `Word`. Larger sets are stored as a collection of such
+    dense small sets, connected together by a prefix trie.
+
+## 0.4.2.1  *Feb 2012*
+
+  * Bundled with GHC 7.4.1.
+
+  * `Data.Map now exports `foldr`, `foldr'`, `foldl` and `foldl'`.
+
+  * `Data.Set now exports `foldr`, `foldr'`, `foldl` and `foldl'`.
+
+  * `Data.IntMap now exports `foldr`, `foldr'`, `foldl`, `foldl'`, `foldrWithKey`, `foldrWithKey'`, `foldlWithKey` and `foldlWithKey'`.
+
+  * `Data.IntSet now exports `foldr`, `foldr'`, `foldl` and `foldl'`.
+
+  * `Data.Map.foldWithKey` is no longer deprecated, although it is expected to be deprecated again in the future.
+
+  * There are now `NFData` instance for `Data.Map.Map`, `Data.Set.Set`, `Data.IntMap.IntMap`, `Data.IntSet.IntSet` and `Data.Tree.Tree`.
+
+## 0.4.1.0  *Aug 2011*
+
+  * Bundled with GHC 7.2.1.
+
+  * `Data.Map` now exports new functions `foldrWithKey'` and `foldlWithKey'`, which are strict variants of `foldrWithKey` and `foldlWithKey` respectively.
+
+  * `Data.IntMap` now exports new functions `insertWith'` and `insertWithKey'`, which are strict variants of `insertWith` and `insertWithKey` respectively.
+
+## 0.4.0.0  *Nov 2010*
+
+  * Bundled with GHC 7.0.1.
+
+  * Strictness is now more consistent, with containers being strict in their elements even in singleton cases.
+
+  * There is a new function `insertLookupWithKey'` in `Data.Map`.
+
+  * The `foldWithKey` function in `Data.Map` has been deprecated in favour of `foldrWithKey`.
+
+## 0.3.0.0  *Dec 2009*
+
+  * Bundled with GHC 6.12.1.
+
+  * `mapAccumRWithKey` has been added to `Data.IntMap`.
+
+  * A `Traversable` instance has been added to `Data.IntMap.IntMap`.
+
+  * The types of `Data.IntMap.intersectionWith` and `Data.IntMap.intersectionWithKey` have been changed from
+    `intersectionWith :: (a -> b -> a) -> IntMap a -> IntMap b -> IntMap a`
+    `intersectionWithKey :: (Key -> a -> b -> a) -> IntMap a -> IntMap b -> IntMap a`
+    to
+    `intersectionWith :: (a -> b -> c) -> IntMap a -> IntMap b -> IntMap c`
+    `intersectionWithKey :: (Key -> a -> b -> c) -> IntMap a -> IntMap b -> IntMap c`
+
+  * The types of `Data.IntMap.findMin` and `Data.IntMap.findMax` have been changed from
+    `findMin :: IntMap a -> a`
+    `findMax :: IntMap a -> a`
+    to
+    `findMin :: IntMap a -> (Int,a)`
+    `findMax :: IntMap a -> (Int,a)`
+
+  * `Data.Map` now exports `mapAccumRWithKey`, `foldrWithKey`, `foldlWithKey` and `toDescList`.
+
+  * `Data.Sequence` now exports `replicate`, `replicateA`, `replicateM`, `iterateN`, `unfoldr`, `unfoldl`, `scanl`, `scanl1`, `scanr`, `scanr1`, `tails`, `inits`, `takeWhileL`, `takeWhileR`, `dropWhileL`, `dropWhileR`, `spanl`, `spanr`, `breakl`, `breakr`, `partition`, `filter`, `sort`, `sortBy`, `unstableSort`, `unstableSortBy`, `elemIndexL`, `elemIndicesL`, `elemIndexR`, `elemIndicesR`, `findIndexL`, `findIndicesL`, `findIndexR`, `findIndicesR`, `foldlWithIndex`, `foldrWithIndex`, `mapWithIndex`, `zip`, `zipWith`, `zip3`, `zipWith3`, `zip4` and `zipWith4`.
+
+## 0.2.0.0  *Nov 2008*
+
+  * Bundled with GHC 6.10.1.
+
+  * Various result type now use `Maybe` rather than allowing any `Monad`.
+
+## 0.1.0.0  *Nov 2007*
+
+  * Bundled with GHC 6.8.1.
+
+  * Initial split off from GHC base.