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.. _release-9-8-1:
Version 9.8.1
=============
Language
~~~~~~~~
- There is a new extension :extension:`ExtendedLiterals`, which enables
sized primitive literals, e.g. ``123#Int8`` is a literal of type ``Int8#``.
See the GHC proposal `#451 <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0451-sized-literals.rst>`_.
Compiler
~~~~~~~~
- Added a new warning :ghc-flag:`-Wterm-variable-capture` that helps to make code compatible with
the future extension ``RequiredTypeArguments``.
- Rewrite rules now support a limited form of higher order matching when a
pattern variable is applied to distinct locally bound variables. For example: ::
forall f. foo (\x -> f x)
Now matches: ::
foo (\x -> x*2 + x)
- GHC Proposal `#496
<https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0496-empty-record-wildcards.rst>`_
has been implemented, allowing ``{..}`` syntax for constructors without fields, for consistency.
This is convenient for TH code generation, as you can now uniformly use record wildcards
regardless of number of fields.
- Incoherent instance applications are no longer specialised. The previous implementation of
specialisation resulted in nondeterministic instance resolution in certain cases, breaking
the specification described in the documentation of the `INCOHERENT` pragma. See GHC ticket
#22448 for further details.
- Fix a bug in TH causing excessive calls to ``setNumCapabilities`` when ``-j`` is greater than ``-N``.
See GHC ticket #23049.
- The ``-Wno-⟨wflag⟩``, ``-Werror=⟨wflag⟩`` and ``-Wwarn=⟨wflag⟩`` options are
now defined systematically for all warning groups (for example,
``-Wno-default``, ``-Werror=unused-binds`` and ``-Wwarn=all`` are now
accepted). See :ref:`options-sanity`.
- ``WARNING`` pragmas may now be annotated with a category, following
`GHC proposal #541 <https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0541-warning-pragmas-with-categories.rst>`_, in which case they are controlled with new
``-Wx-⟨category⟩`` flags rather than :ghc-flag:`-Wdeprecations`.
A new warning group :ghc-flag:`-Wextended-warnings` includes all such warnings
regardless of category. See :ref:`warning-deprecated-pragma`.
- GHC is now better at disambiguating record updates in the presence of duplicate
record fields. The following program is now accepted ::
{-# LANGUAGE DuplicateRecordFields #-}
data R = MkR1 { foo :: Int }
| MkR2 { bar :: Int }
data S = MkS { foo :: Int, bar :: Int }
blah x = x { foo = 5, bar = 6 }
The point is that only the type S has a constructor with both fields "foo"
and "bar", so this record update is unambiguous.
- Data types with ``deriving`` clauses now reject inferred instance contexts
that mention ``TypeError`` constraints (see :ref:`custom-errors`), such as
this one: ::
newtype Foo = Foo Int
class Bar a where
bar :: a
instance (TypeError (Text "Boo")) => Bar Foo where
bar = undefined
newtype Baz = Baz Foo
deriving Bar
Here, the derived ``Bar`` instance for ``Baz`` would look like this: ::
instance TypeError (Text "Boo") => Bar Baz
While GHC would accept this before, GHC 9.8 now rejects it, emitting "``Boo``"
in the resulting error message. If you really want to derive this instance and
defer the error to sites where the instance is used, you must do so manually
with :extension:`StandaloneDeriving`, e.g. ::
deriving instance TypeError (Text "Boo") => Bar Baz
- GHC Proposal `#540 https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0540-jsem.rst`_ has been implemented.
This adds the `-jsem`:ghc-flag: flag, which instructs GHC to act as a jobserver client.
This enables multiple GHC processes running at once to share system resources
with each other, communicating via the system semaphore specified by
the flag argument.
- GHC Proposal `#433
<https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0433-unsatisfiable.rst>`_
has been implemented. This adds the class ``Unsatisfiable :: ErrorMessage -> Constraint``
to the ``GHC.TypeError`` module. Constraints of the form ``Unsatisfiable msg``
provide a mechanism for custom type errors that reports the errors in a more
predictable behaviour than ``TypeError``, as these constraints are
handled purely during constraint solving.
For example: ::
instance Unsatisfiable (Text "There is no Eq instance for functions") => Eq (a -> b) where
(==) = unsatisfiable
This allows errors to be reported when users use the instance, even when
type errors are being deferred.
GHCi
~~~~
Runtime system
~~~~~~~~~~~~~~
- On POSIX systems that support timerfd, RTS shutdown no longer has to wait for
the next RTS 'tick' to occur before continuing the shutdown process. See #22692.
``base`` library
~~~~~~~~~~~~~~~~
- ``Data.Tuple`` now exports ``getSolo :: Solo a -> a``.
``ghc-prim`` library
~~~~~~~~~~~~~~~~~~~~
- Primitive pointer comparison functions are now levity-polymorphic, e.g. ::
sameArray# :: forall {l} (a :: TYPE (BoxedRep l)). Array# a -> Array# a -> Int#
This change affects the following functions:
- ``sameArray#``, ``sameMutableArray#``,
- ``sameSmallArray#``, ``sameSmallMutableArray#``,
- ``sameMutVar#``, ``sameTVar#``, ``sameMVar#``
- ``sameIOPort#``, ``eqStableName#``.
- New primops for fused multiply-add operations. These primops combine a
multiplication and an addition, compiling to a single instruction when
the ``-mfma`` flag is enabled and the architecture supports it.
The new primops are ``fmaddFloat#, fmsubFloat#, fnmaddFloat#, fnmsubFloat# :: Float# -> Float# -> Float# -> Float#``
and ``fmaddDouble#, fmsubDouble#, fnmaddDouble#, fnmsubDouble# :: Double# -> Double# -> Double# -> Double#``.
These implement the following operations, while performing one single
rounding at the end, leading to a more accurate result:
- ``fmaddFloat# x y z``, ``fmaddDouble# x y z`` compute ``x * y + z``.
- ``fmsubFloat# x y z``, ``fmsubDouble# x y z`` compute ``x * y - z``.
- ``fnmaddFloat# x y z``, ``fnmaddDouble# x y z`` compute ``- x * y + z``.
- ``fnmsubFloat# x y z``, ``fnmsubDouble# x y z`` compute ``- x * y - z``.
Warning: on unsupported architectures, the software emulation provided by
the fallback to the C standard library is not guaranteed to be IEEE-compliant.
``ghc`` library
~~~~~~~~~~~~~~~
- The ``RecordUpd`` constructor of ``HsExpr`` now takes an ``HsRecUpdFields``
instead of ``Either [LHsRecUpdField p] [LHsRecUpdProj p]``.
Instead of ``Left ..``, use the constructor ``RegularRecUpdFields``, and instead
of ``Right ..``, use the constructor ``OverloadedRecUpdFields``.
``ghc-heap`` library
~~~~~~~~~~~~~~~~~~~~
``template-haskell`` library
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
- Record fields now belong to separate ``NameSpace``s, keyed by the parent of
the record field. This is the name of the first constructor of the parent type,
even if this constructor does not have the field in question.
This change enables TemplateHaskell support for ``DuplicateRecordFields``.
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: Dependency of ``ghc`` library
libraries/Cabal/Cabal/Cabal.cabal: Dependency of ``ghc-pkg`` utility
libraries/Cabal/Cabal-syntax/Cabal-syntax.cabal: Dependency of ``ghc-pkg`` utility
libraries/containers/containers/containers.cabal: Dependency of ``ghc`` library
libraries/deepseq/deepseq.cabal: Dependency of ``ghc`` library
libraries/directory/directory.cabal: Dependency of ``ghc`` library
libraries/exceptions/exceptions.cabal: Dependency of ``ghc`` and ``haskeline`` 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-boot-th/ghc-boot-th.cabal: Internal compiler library
libraries/ghc-compact/ghc-compact.cabal: Core library
libraries/ghc-heap/ghc-heap.cabal: GHC heap-walking 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/pretty/pretty.cabal: Dependency of ``ghc`` library
libraries/process/process.cabal: Dependency of ``ghc`` library
libraries/stm/stm.cabal: Dependency of ``haskeline`` library
libraries/template-haskell/template-haskell.cabal: Core library
libraries/terminfo/terminfo.cabal: Dependency of ``haskeline`` 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
|
