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.. _release-8-6-1:
Release notes for version 8.6.1
===============================
The significant changes to the various parts of the compiler are listed in the
following sections. There have also been numerous bug fixes and performance
improvements over the 8.4.1 release.
Highlights
----------
The highlights, since the 8.4.1 release, are:
- Many, many bug fixes.
Full details
------------
Language
~~~~~~~~
- GHC now permits the use of a wildcard type as the context of a standalone
``deriving`` declaration with the use of the
:extension:`PartialTypeSignatures` language extension. For instance, this
declaration: ::
deriving instance _ => Eq (Foo a)
Denotes a derived ``Eq (Foo a)`` instance, where the context is inferred in
much the same way as ordinary ``deriving`` clauses do.
See :ref:`partial-type-signatures`.
- Data declarations with empty ``where`` clauses are no longer valid without the
extension :extension:`GADTSyntax` enabled. For instance, consider the
following, ::
data T where
The grammar is invalid in Haskell2010. Previously it could be compiled successfully
without ``GADTs``. As of GHC 8.6.1, this is a parse error.
- Incomplete patterns warning :ghc-flag:`-Wincomplete-patterns` is extended to
guards in pattern bindings and ``if`` alternatives of :extension:`MultiWayIf`.
For instance, consider the following, ::
foo :: Bool -> Int
foo b = if | b -> 1
In GHC 8.6.1, it will raise the warning: ::
<interactive>:2:12: warning: [-Wincomplete-patterns]
Pattern match(es) are non-exhaustive
In a multi-way if alternative:
Guards do not cover entire pattern space
See :ghc-ticket:`14773`.
- Scoped type variables now work in default methods of class declarations
and in pattern synonyms in Template Haskell. See :ghc-ticket:`14885`.
Compiler
~~~~~~~~
- GHC now no longer adds the current file's directory as a general include path
calling the C compiler. Instead we use :ghc-flag:`-iquote` to only add it as
an include path for `#include ""`. See :ghc-ticket:`14312`.
- GHC now supports British spelling of :extension:`GeneralizedNewtypeDeriving`.
- The code-generation effects of :ghc-flag:`-dynamic` can now be
enabled independently by the flag
:ghc-flag:`-fexternal-dynamic-refs`. If you don't know why you might
need this, you don't need it.
Runtime system
~~~~~~~~~~~~~~
- The GHC runtime linker now prefers user shared libraries above system ones.
When extra search directories are specified these are searched before anything
else. This fixes ``iuuc`` on Windows given the proper search directories (e.g
``-L/mingw64/lib``).
- The GHC runtime linker now uses ``LIBRARY_PATH`` and the runtime loader now also
searches ``LD_LIBRARY_PATH``.
- The GHC runtime on Windows is no longer constrained by MAX_PATH.
Template Haskell
~~~~~~~~~~~~~~~~
``ghc`` library
~~~~~~~~~~~~~~~
``base`` library
~~~~~~~~~~~~~~~~
- ``($!)`` is now representation-polymorphic like ``($)``.
- The module ``Data.Functor.Contravariant`` has been moved from the
``contravariant`` package into base. All the other modules in
``contravariant`` (``Data.Functor.Contravariant.Divisible``, etc.)
have not been moved to ``base``, and they still reside in ``contravariant``.
Build system
~~~~~~~~~~~~
Windows Paths
~~~~~~~~~~~~~
Windows paths are not all the same. The different kinds of paths each have
different meanings. The MAX_PATH limitation is not a limitation of the Operating
System nor the File System. It is a limitation of the default namespace enforced
by the Win32 API for backwards compatibility.
The NT Kernel however allows you ways to opt out of this path preprocessing by
the Win32 APIs. This is done by explicitly using the desired namespace in the
PATH.
The namespaces are:
- file namespace: \\?\
- device namespace: \\.\
- nt namespace: \
Each of these turn off Path processing completely by the Win32 API and the paths
are passed untouched to the filesystem.
Paths with a drive letter are `legacy` paths. The drive letters are actually
meaningless to the kernel. Just like Unix operating systems, drive letters are
just a mount point. You can view your mount points by using the `mountvol`
command.
The Haskell I/O manager will now automatically promote paths in the legacy
format to Win32 file namespace. By default the I/O manager will do two things to
your paths:
- replace / with \\
- expand relative paths to absolute paths
If you want to opt out of all preprocessing just expliticly use namespaces in
your paths. Due to this change, if you need to open raw devices (e.g. COM ports)
you need to use the device namespace explicitly. (e.g. `\\.\COM1`). GHC and
Haskell programs in general no longer support opening devices in the `legacy`
format.
See https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247.aspx for
more details.
Included libraries
------------------
The package database provided with this distribution also contains a number of
packages other than GHC itself. See the changelogs provided with these packages
for further change information.
.. ghc-package-list::
libraries/array/array.cabal: Dependency of ``ghc`` library
libraries/base/base.cabal: Core library
libraries/binary/binary.cabal: Dependency of ``ghc`` library
libraries/bytestring/bytestring.cabal: Deppendency of ``ghc`` library
libraries/Cabal/Cabal/Cabal.cabal: Dependency of ``ghc-pkg`` utility
libraries/containers/containers.cabal: Dependency of ``ghc`` library
libraries/deepseq/deepseq.cabal: Dependency of ``ghc`` library
libraries/directory/directory.cabal: Dependency of ``ghc`` library
libraries/filepath/filepath.cabal: Dependency of ``ghc`` library
compiler/ghc.cabal: The compiler itself
libraries/ghci/ghci.cabal: The REPL interface
libraries/ghc-boot/ghc-boot.cabal: Internal compiler library
libraries/ghc-compact/ghc-compact.cabal: Core library
libraries/ghc-prim/ghc-prim.cabal: Core library
libraries/haskeline/haskeline.cabal: Dependency of ``ghci`` executable
libraries/hpc/hpc.cabal: Dependency of ``hpc`` executable
libraries/integer-gmp/integer-gmp.cabal: Core library
libraries/mtl/mtl.cabal: Dependency of ``Cabal`` library
libraries/parsec/parsec.cabal: Dependency of ``Cabal`` library
libraries/process/process.cabal: Dependency of ``ghc`` library
libraries/template-haskell/template-haskell.cabal: Core library
libraries/text/text.cabal: Dependency of ``Cabal`` library
libraries/time/time.cabal: Dependency of ``ghc`` library
libraries/transformers/transformers.cabal: Dependency of ``ghc`` library
libraries/unix/unix.cabal: Dependency of ``ghc`` library
libraries/Win32/Win32.cabal: Dependency of ``ghc`` library
libraries/xhtml/xhtml.cabal: Dependency of ``haddock`` executable
|
