[ANNOUNCE] GHC 8.0.1 release candidate 4 available

[Ben Gamari]

Hello Haskellers,

The GHC team is happy to announce the availability of fourth release
candidate of the Glasgow Haskell Compiler's 8.0.1 release. Source and
binary distributions can be found at,

    http://downloads.haskell.org/~ghc/8.0.1-rc4/

This is the last of four candidates leading up to the 8.0.1 release,
addressing nearly all of the known issues of the previous candidates.
These include,

  * A type-checker panic triggered by use of Typeable on a
    kind-polymorphic type constructor (#11334)

  * A type-checker explosion where -XTypeInType would gobble up massive
    amounts of memory when used in a data instance (#11407)

  * A variety of other typechecker issues (#11811, #11797, #11813,
    #11814)

  * A build issue seen on OS X (#11828)

  * Template Haskell can now produce instances with
    OVERLAPP{ING,ABLE,ED} pragmas

  * Autoconf has improved version checks for libdw (#11820)

  * Typeable and hs-boot files now interact nicely (#11824)

  * The build system now checks for the broken Apple `nm` utility
    (#11823, #11744)

  * Various issues involving unexpected laziness resulting in exception
    handlers not being invoked (#11555)

  * GHC now fails more gracefully when used with an older cabal-install
    release (#11558)

  * TypeInType now has proper documentation in the users guide (#11614)

  * The story surrounding type `RuntimeRep`s (formerly known as
    `Levity`) is now far better developed, closing several doors to
    unsafe behavior that TypeInType previously opened (#11473, #11723)

  * A long-standing bug in the constant-folding rules for `mod` for the
    `Word` type has been resolved (#11702)

  * Various issues introduced by OverloadedRecordFields have been fixed
    (#11662, #11401) 

  * A regression in the typechecker resulting in the rejection of code
    in the `free` and `microlens` packages has been fixed (#11608)

  * A bug in the LLVM code generator which caused some programs to emit
    unbuildable LLVM IR has been fixed (#11649)

  * A bug where pattern synonyms defined in terms of a pattern match on
    a record would be rejected if the fields weren't written in the same order
    as they were defined has been resolved (#11633)

  * A bug in the runtime system's treatment of weak references which
    could result in segmentation faults in some cases has been fixed (#11108)

  * a variety of optimizations improving compiler performance have been
    merged

  * and many others

Mac OS X users should be aware that the recent XCode 7.3 release ships
with a broken `nm` utility which breaks the GHC build (#11744, #11823).
The build system will check for this condition and request that the tree
is configured to use the `nm-classic` utility if found. OS X users
running XCode 7.3 are encouraged to open a ticket with Apple so that
this issue may be fixed in future XCode releases.

If no major issues pop up we expect that this will be the last release
candidate before the final release, which we hope to push out in the
coming weeks. Thanks to everyone who has contributed code, testing,
builds, and bug reports thusfar!

Cheers and happy testing,

- Ben
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