[ANNOUNCE] GHC 8.0.1 release candidate 3 available

[Ben Gamari]

Hello Haskellers,

The GHC team is happy to announce the availability of third 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-rc3/

This is the third of what will be four candidates leading up to the
8.0.1 release. As there are a number of known issues with this
candidate, we expect to produce the fourth and final release candidate
shortly. While we considered not releasing this candidate at all and
instead skipping to rc4, we decided that it would be helpful to make it
available despite its issues to increase the likelihood of catching any
remaining bugs.

That being said, this candidate lacks the range of binary distributions
which we usually offer,

  * We are unable to release Windows bindists due to a compatibility
    issue which we didn't catch until after preparing the source
    distribution.

  * Binaries targeting Redhat distributions are currently not available

Regardless, users for whom a distribution is available are encouraged to
try this candidate as it fixes dozens of issues present in release
candidate two. 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)

  * 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).
Unfortunately, this candidate does not notice this brokenness and odd
behavior can result. OS X users running XCode 7.3 are encouraged to open
a ticket with Apple and build GHC with the `--with-nm=nm-classic`
configure option until a fix is available.

As mentioned earlier, there are a number of known issues with this
candidate which will be addressed in release candidate four. These
issues include,

  * A number of typechecker bugs (#11811, #11797, #11813, #11814)

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

  * Template Haskell lacks the ability to produce instances with
    OVERLAPP{ING,ABLE,ED} pragmas

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

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

  * The build system doesn't check for the broken Apple `nm` utility,
    leading to unpredictable results (#11823, #11744)

We hope to have release candidate four available by the middle of next
week.

Thanks to everyone who has contributed code, testing, builds, and bug
reports thusfar!

Cheers,

- Ben
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