# Changelog for [`base` package](http://hackage.haskell.org/package/base)
## 4.9.0.0 *TBA*
* Bundled with GHC 8.0
* `error` and `undefined` now print a partial stack-trace alongside the error message.
* New `errorWithoutStackTrace` function throws an error without printing the stack trace.
* The restore operation provided by `mask` and `uninterruptibleMask` now
restores the previous masking state whatever the current masking state is.
* New `GHC.Generics.packageName` operation
* Redesigned `GHC.Stack.CallStack` data type. As a result, `CallStack`'s
`Show` instance produces different output, and `CallStack` no longer has an
`Eq` instance.
* New `GHC.Generics.packageName` operation
* New `GHC.Stack.Types` module now contains the definition of
`CallStack` and `SrcLoc`
* New `GHC.Stack.Types.emptyCallStack` function builds an empty `CallStack`
* New `GHC.Stack.Types.freezeCallStack` function freezes a `CallStack` preventing future `pushCallStack` operations from having any effect
* New `GHC.Stack.Types.pushCallStack` function pushes a call-site onto a `CallStack`
* New `GHC.Stack.Types.fromCallSiteList` function creates a `CallStack` from
a list of call-sites (i.e., `[(String, SrcLoc)]`)
* `GHC.SrcLoc` has been removed
* `GHC.Stack.showCallStack` and `GHC.SrcLoc.showSrcLoc` are now called
`GHC.Stack.prettyCallStack` and `GHC.Stack.prettySrcLoc` respectively
* add `Data.List.NonEmpty` and `Data.Semigroup` (to become
super-class of `Monoid` in the future). These modules were
provided by the `semigroups` package previously. (#10365)
* Add `selSourceUnpackedness`, `selSourceStrictness`, and
`selDecidedStrictness`, three functions which look up strictness
information of a field in a data constructor, to the `Selector` type class
in `GHC.Generics` (#10716)
* Add `URec`, `UAddr`, `UChar`, `UDouble`, `UFloat`, `UInt`, and `UWord` to
`GHC.Generics` as part of making GHC generics capable of handling
unlifted types (#10868)
* Keep `shift{L,R}` on `Integer` with negative shift-arguments from
segfaulting (#10571)
* Add `forkOSWithUnmask` to `Control.Concurrent`, which is like
`forkIOWithUnmask`, but the child is run in a bound thread.
* The `MINIMAL` definition of `Arrow` is now `arr AND (first OR (***))`.
* The `MINIMAL` definition of `ArrowChoice` is now `left OR (+++)`.
* Exported `GiveGCStats`, `DoCostCentres`, `DoHeapProfile`, `DoTrace`,
`RtsTime`, and `RtsNat` from `GHC.RTS.Flags`
* New function `GHC.IO.interruptible` used to correctly implement
`Control.Exception.allowInterrupt` (#9516)
* Made `PatternMatchFail`, `RecSelError`, `RecConError`, `RecUpdError`,
`NoMethodError`, and `AssertionFailed` newtypes (#10738)
* New module `Control.Monad.IO.Class` (previously provided by `transformers`
package). (#10773)
* New modules `Data.Functor.Classes`, `Data.Functor.Compose`,
`Data.Functor.Product`, and `Data.Functor.Sum` (previously provided by
`transformers` package). (#11135)
* New module `Control.Monad.Fail` providing new `MonadFail(fail)`
class (#10751)
* Add `GHC.TypeLits.TypeError` and `ErrorMessage` to allow users
to define custom compile-time error messages.
* Redesign `GHC.Generics` to use type-level literals to represent the
metadata of generic representation types (#9766)
* The `IsString` instance for `[Char]` has been modified to eliminate
ambiguity arising from overloaded strings and functions like `(++)`.
* Move `Const` from `Control.Applicative` to its own module in
`Data.Functor.Const`. (#11135)
* Re-export `Const` from `Control.Applicative` for backwards compatibility.
* Expand `Floating` class to include operations that allow for better
precision: `log1p`, `expm1`, `log1pexp` and `log1mexp`. These are not
available from `Prelude`, but the full class is exported from `Numeric`.
* New `Control.Exception.TypeError` datatype, which is thrown when an
expression fails to typecheck when run using `-fdefer-type-errors` (#10284)
### New instances
* `Alt`, `Dual`, `First`, `Last`, `Product`, and `Sum` now have `Data`,
`MonadZip`, and `MonadFix` instances
* `Maybe` now has a `MonadZip` instance
* `All` and `Any` now have `Data` instances
* `Dual`, `First`, `Last`, `Product`, and `Sum` now have `Foldable` and
`Traversable` instances
* `Dual`, `Product`, and `Sum` now have `Functor`, `Applicative`, and
`Monad` instances
* `(,) a` now has a `Monad` instance
* `ZipList` now has `Foldable` and `Traversable` instances
* `Identity` now has `Semigroup` and `Monoid` instances
* `Identity` and `Const` now have `Bounded`, `Enum` and `Ix` instances
* `Identity` and `Const` now have `Storable` instances
* `()` now has a `Storable` instance
* `Complex` now has `Generic`, `Generic1`, `Functor`, `Foldable`, `Traversable`,
`Applicative`, and `Monad` instances
* `System.Exit.ExitCode` now has a `Generic` instance
* `Data.Version.Version` now has a `Generic` instance
* `IO` now has a `Monoid` instance
* Add `MonadPlus IO` and `Alternative IO` instances
(previously orphans in `transformers`) (#10755)
* `CallStack` now has an `IsList` instance
### Generalizations
* Generalize `Debug.Trace.{traceM, traceShowM}` from `Monad` to `Applicative`
(#10023)
* Redundant typeclass constraints have been removed:
- `Data.Ratio.{denominator,numerator}` have no `Integral` constraint anymore
- **TODO**
* Generalise `forever` from `Monad` to `Applicative`
* Generalize `filterM`, `mapAndUnzipM`, `zipWithM`, `zipWithM_`, `replicateM`,
`replicateM_` from `Monad` to `Applicative` (#10168)
* The `Generic` instance for `Proxy` is now poly-kinded (#10775)
* Enable `PolyKinds` in the `Data.Functor.Const` module to give `Const`
the kind `* -> k -> *`. (#10039)
## 4.8.2.0 *Oct 2015*
* Bundled with GHC 7.10.3
* The restore operation provided by `mask` and `uninterruptibleMask` now
restores the previous masking state whatever the current masking state is.
* Exported `GiveGCStats`, `DoCostCentres`, `DoHeapProfile`, `DoTrace`,
`RtsTime`, and `RtsNat` from `GHC.RTS.Flags`
## 4.8.1.0 *Jul 2015*
* Bundled with GHC 7.10.2
* `Lifetime` is now exported from `GHC.Event`
* Implicit-parameter based source location support exposed in `GHC.SrcLoc` and `GHC.Stack`.
See GHC User's Manual for more information.
## 4.8.0.0 *Mar 2015*
* Bundled with GHC 7.10.1
* Make `Applicative` a superclass of `Monad`
* Add reverse application operator `Data.Function.(&)`
* Add `Data.List.sortOn` sorting function
* Add `System.Exit.die`
* Deprecate `versionTags` field of `Data.Version.Version`.
Add `makeVersion :: [Int] -> Version` constructor function to aid
migration to a future `versionTags`-less `Version`.
* Add `IsList Version` instance
* Weaken RealFloat constraints on some `Data.Complex` functions
* Add `Control.Monad.(<$!>)` as a strict version of `(<$>)`
* The `Data.Monoid` module now has the `PolyKinds` extension
enabled, so that the `Monoid` instance for `Proxy` are polykinded
like `Proxy` itself is.
* Make `abs` and `signum` handle (-0.0) correctly per IEEE-754.
* Re-export `Data.Word.Word` from `Prelude`
* Add `countLeadingZeros` and `countTrailingZeros` methods to
`Data.Bits.FiniteBits` class
* Add `Data.List.uncons` list destructor (#9550)
* Export `Monoid(..)` from `Prelude`
* Export `Foldable(..)` from `Prelude`
(hiding `fold`, `foldl'`, `foldr'`, and `toList`)
* Export `Traversable(..)` from `Prelude`
* Set fixity for `Data.Foldable.{elem,notElem}` to match the
conventional one set for `Data.List.{elem,notElem}` (#9610)
* Turn `toList`, `elem`, `sum`, `product`, `maximum`, and `minimum`
into `Foldable` methods (#9621)
* Replace the `Data.List`-exported functions
```
all, and, any, concat, concatMap, elem, find, product, sum,
mapAccumL, mapAccumR
```
by re-exports of their generalised `Data.Foldable`/`Data.Traversable`
counterparts. In other words, unqualified imports of `Data.List`
and `Data.Foldable`/`Data.Traversable` no longer lead to conflicting
definitions. (#9586)
* New (unofficial) module `GHC.OldList` containing only list-specialised
versions of the functions from `Data.List` (in other words, `GHC.OldList`
corresponds to `base-4.7.0.2`'s `Data.List`)
* Replace the `Control.Monad`-exported functions
```
sequence_, msum, mapM_, forM_,
forM, mapM, sequence
```
by re-exports of their generalised `Data.Foldable`/`Data.Traversable`
counterparts. In other words, unqualified imports of `Control.Monad`
and `Data.Foldable`/`Data.Traversable` no longer lead to conflicting
definitions. (#9586)
* Generalise `Control.Monad.{when,unless,guard}` from `Monad` to
`Applicative` and from `MonadPlus` to `Alternative` respectively.
* Generalise `Control.Monad.{foldM,foldM_}` to `Foldable`
* `scanr`, `mapAccumL` and `filterM` now take part in list fusion (#9355,
#9502, #9546)
* Remove deprecated `Data.OldTypeable` (#9639)
* New module `Data.Bifunctor` providing the `Bifunctor(bimap,first,second)`
class (previously defined in `bifunctors` package) (#9682)
* New module `Data.Void` providing the canonical uninhabited type `Void`
(previously defined in `void` package) (#9814)
* Update Unicode class definitions to Unicode version 7.0
* Add `Alt`, an `Alternative` wrapper, to `Data.Monoid`. (#9759)
* Add `isSubsequenceOf` to `Data.List` (#9767)
* The arguments to `==` and `eq` in `Data.List.nub` and `Data.List.nubBy`
are swapped, such that `Data.List.nubBy (<) [1,2]` now returns `[1]`
instead of `[1,2]` (#2528, #3280, #7913)
* New module `Data.Functor.Identity` (previously provided by `transformers`
package). (#9664)
* Add `scanl'`, a strictly accumulating version of `scanl`, to `Data.List`
and `Data.OldList`. (#9368)
* Add `fillBytes` to `Foreign.Marshal.Utils`.
* Add new `displayException` method to `Exception` typeclass. (#9822)
* Add `Data.Bits.toIntegralSized`, a size-checked version of
`fromIntegral`. (#9816)
* New module `Numeric.Natural` providing new `Natural` type
representing non-negative arbitrary-precision integers. The `GHC.Natural`
module exposes additional GHC-specific primitives. (#9818)
* Add `(Storable a, Integeral a) => Storable (Ratio a)` instance (#9826)
* Add `Storable a => Storable (Complex a)` instance (#9826)
* New module `GHC.RTS.Flags` that provides accessors to runtime flags.
* Expose functions for per-thread allocation counters and limits in `GHC.Conc`
disableAllocationLimit :: IO ()
enableAllocationLimit :: IO ()
getAllocationCounter :: IO Int64
setAllocationCounter :: Int64 -> IO ()
together with a new exception `AllocationLimitExceeded`.
* Make `read . show = id` for `Data.Fixed` (#9240)
* Add `calloc` and `callocBytes` to `Foreign.Marshal.Alloc`. (#9859)
* Add `callocArray` and `callocArray0` to `Foreign.Marshal.Array`. (#9859)
* Restore invariant in `Data (Ratio a)` instance (#10011)
* Add/expose `rnfTypeRep`, `rnfTyCon`, `typeRepFingerprint`, and
`tyConFingerprint` helpers to `Data.Typeable`.
* Define proper `MINIMAL` pragma for `class Ix`. (#10142)
## 4.7.0.2 *Dec 2014*
* Bundled with GHC 7.8.4
* Fix performance bug in `Data.List.inits` (#9345)
* Fix handling of null bytes in `Debug.Trace.trace` (#9395)
## 4.7.0.1 *Jul 2014*
* Bundled with GHC 7.8.3
* Unhide `Foreign.ForeignPtr` in Haddock (#8475)
* Fix recomputation of `TypeRep` in `Typeable` type-application instance
(#9203)
* Fix regression in Data.Fixed Read instance (#9231)
* Fix `fdReady` to honor `FD_SETSIZE` (#9168)
## 4.7.0.0 *Apr 2014*
* Bundled with GHC 7.8.1
* Add `/Since: 4.[4567].0.0/` Haddock annotations to entities
denoting the package version, when the given entity was introduced
(or its type signature changed in a non-compatible way)
* The `Control.Category` module now has the `PolyKinds` extension
enabled, meaning that instances of `Category` no longer need be of
kind `* -> * -> *`.
* There are now `Foldable` and `Traversable` instances for `Either a`,
`Const r`, and `(,) a`.
* There are now `Show`, `Read`, `Eq`, `Ord`, `Monoid`, `Generic`, and
`Generic1` instances for `Const`.
* There is now a `Data` instance for `Data.Version`.
* A new `Data.Bits.FiniteBits` class has been added to represent
types with fixed bit-count. The existing `Bits` class is extended
with a `bitSizeMaybe` method to replace the now obsolete
`bitsize` method.
* `Data.Bits.Bits` gained a new `zeroBits` method which completes the
`Bits` API with a direct way to introduce a value with all bits cleared.
* There are now `Bits` and `FiniteBits` instances for `Bool`.
* There are now `Eq`, `Ord`, `Show`, `Read`, `Generic`. and `Generic1`
instances for `ZipList`.
* There are now `Eq`, `Ord`, `Show` and `Read` instances for `Down`.
* There are now `Eq`, `Ord`, `Show`, `Read` and `Generic` instances
for types in GHC.Generics (`U1`, `Par1`, `Rec1`, `K1`, `M1`,
`(:+:)`, `(:*:)`, `(:.:)`).
* `Data.Monoid`: There are now `Generic` instances for `Dual`, `Endo`,
`All`, `Any`, `Sum`, `Product`, `First`, and `Last`; as well as
`Generic1` instances for `Dual`, `Sum`, `Product`, `First`, and `Last`.
* The `Data.Monoid.{Product,Sum}` newtype wrappers now have `Num` instances.
* There are now `Functor` instances for `System.Console.GetOpt`'s
`ArgOrder`, `OptDescr`, and `ArgDescr`.
* A zero-width unboxed poly-kinded `Proxy#` was added to
`GHC.Prim`. It can be used to make it so that there is no the
operational overhead for passing around proxy arguments to model
type application.
* New `Data.Proxy` module providing a concrete, poly-kinded proxy type.
* New `Data.Coerce` module which exports the new `Coercible` class
together with the `coerce` primitive which provide safe coercion
(wrt role checking) between types with same representation.
* `Control.Concurrent.MVar` has a new implementation of `readMVar`,
which fixes a long-standing bug where `readMVar` is only atomic if
there are no other threads running `putMVar`. `readMVar` now is
atomic, and is guaranteed to return the value from the first
`putMVar`. There is also a new `tryReadMVar` which is a
non-blocking version.
* New `Control.Concurrent.MVar.withMVarMasked` which executes
`IO` action with asynchronous exceptions masked in the same style
as the existing `modifyMVarMasked` and `modifyMVarMasked_`.
* New `threadWait{Read,Write}STM :: Fd -> IO (STM (), IO ())`
functions added to `Control.Concurrent` for waiting on FD
readiness with STM actions.
* Expose `Data.Fixed.Fixed`'s constructor.
* There are now byte endian-swapping primitives
`byteSwap{16,32,64}` available in `Data.Word`, which use
optimized machine instructions when available.
* `Data.Bool` now exports `bool :: a -> a -> Bool -> a`, analogously
to `maybe` and `either` in their respective modules.
* `Data.Either` now exports `isLeft, isRight :: Either a b -> Bool`.
* `Debug.Trace` now exports `traceId`, `traceShowId`, `traceM`,
and `traceShowM`.
* `Data.Functor` now exports `($>)` and `void`.
* Rewrote portions of `Text.Printf`, and made changes to `Numeric`
(added `Numeric.showFFloatAlt` and `Numeric.showGFloatAlt`) and
`GHC.Float` (added `formatRealFloatAlt`) to support it. The
rewritten version is extensible to user types, adds a "generic"
format specifier "`%v`", extends the `printf` spec to support much
of C's `printf(3)` functionality, and fixes the spurious warnings
about using `Text.Printf.printf` at `(IO a)` while ignoring the
return value. These changes were contributed by Bart Massey.
* The minimal complete definitions for all type-classes with cyclic
default implementations have been explicitly annotated with the
new `{-# MINIMAL #-}` pragma.
* `Control.Applicative.WrappedMonad`, which can be used to convert a
`Monad` to an `Applicative`, has now a
`Monad m => Monad (WrappedMonad m)` instance.
* There is now a `Generic` and a `Generic1` instance for `WrappedMonad`
and `WrappedArrow`.
* Handle `ExitFailure (-sig)` on Unix by killing process with signal `sig`.
* New module `Data.Type.Bool` providing operations on type-level booleans.
* Expose `System.Mem.performMinorGC` for triggering minor GCs.
* New `System.Environment.{set,unset}Env` for manipulating
environment variables.
* Add `Typeable` instance for `(->)` and `RealWorld`.
* Declare CPP header `` officially obsolete as GHC 7.8+
does not support hand-written `Typeable` instances anymore.
* Remove (unmaintained) Hugs98 and NHC98 specific code.
* Optimize `System.Timeout.timeout` for the threaded RTS.
* Remove deprecated functions `unsafeInterleaveST`, `unsafeIOToST`,
and `unsafeSTToIO` from `Control.Monad.ST`.
* Add a new superclass `SomeAsyncException` for all asynchronous exceptions
and makes the existing `AsyncException` and `Timeout` exception children
of `SomeAsyncException` in the hierarchy.
* Remove deprecated functions `blocked`, `unblock`, and `block` from
`Control.Exception`.
* Remove deprecated function `forkIOUnmasked` from `Control.Concurrent`.
* Remove deprecated function `unsafePerformIO` export from `Foreign`
(still available via `System.IO.Unsafe.unsafePerformIO`).
* Various fixes and other improvements (see Git history for full details).