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# Changelog for [`base` package](http://hackage.haskell.org/package/base)

## 4.7.0.0  *Feb 2014*

  * Bundled with GHC 7.8.1

  * 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 is now a `Monoid` instance for `Const`.

  * There is now a `Data` instance for `Data.Version`.

  * There are now `Eq`, `Ord`, `Show` and `Read` 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`,
    `(:+:)`, `(:*:)`, `(:.:)`).

  * 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.

  * `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.

  * There are now byte endian-swapping primitives 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.

  * 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.