-
Ben Gamari authoredBen Gamari authored
.. _release-8-0-1:
Release notes for version 8.0.1
===============================
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 7.10 branch.
Highlights
----------
The highlights, since the 7.10 branch, are:
- TODO FIXME
- nokinds
- Support for :ref:`record pattern synonyms `
- The :ghc-flag:`-XDeriveAnyClass` extension learned to derive instances for
classes with associated types (see :ref:`derive-any-class`)
- More reliable DWARF debugging information
- Support for :ref:`injective type families `
- Applicative ``do`` notation (see :ref:`applicative-do`)
- Support for wildcards in data and type family instances
- :ghc-flag:`-XStrict` and :ghc-flag:`-XStrictData` extensions, allowing modules
to be compiled with strict-by-default bindings (see :ref:`strict-haskell`)
- :ghc-flag:`-XDuplicateRecordFields`, allowing multiple datatypes to declare the same
record field names provided they are used unambiguously (see :ref:`duplicate-record-fields`)
- Support for implicit parameters providing light-weight
:ref:`callstacks and source locations `
- User-defined error messages for type errors
- A rewritten (and greatly improved) pattern exhaustiveness checker
- GHC can run the interpreter in a separate process (see
:ref:`external-interpreter`), and the interpreter can now run profiled
code.
- GHCi now provides access to stack traces when used with
:ghc-flag:`-fexternal-interpreter` and :ghc-flag:`-prof` (see
:ref:`ghci-stack-traces`).
- A native code generator for powerpc64 and powerpc64le architectures
- The reworked users guide you are now reading
- Support for Windows XP and earlier has been dropped.
Full details
------------
Language
~~~~~~~~
- TODO FIXME.
- The parser now supports Haddock comments on GADT data constructors.
For example ::
data Expr a where
-- | Just a normal sum
Sum :: Int -> Int -> Expr Int
- Implicit parameters of the new ``base`` type :base-ref:`GHC.Stack.CallStack `
are treated specially in function calls, the solver automatically
appends the source location of the call to the ``CallStack`` in
the environment. For example ::
myerror :: (?callStack :: CallStack) => String -> a
myerror msg = error (msg ++ "\n" ++ prettyCallStack ?callStack)
ghci> myerror "die"
*** Exception: die
CallStack (from ImplicitParams):
myerror, called at :2:1 in interactive:Ghci1
prints the call-site of ``myerror``. The name of the implicit
parameter does not matter, but within ``base`` we call it
``?callStack``.
See :ref:`lib-base` for a description of the ``CallStack`` type.
- GHC now supports visible type application, allowing
programmers to easily specify how type parameters should be
instantiated when calling a function. See
:ref:`visible-type-application` for the details.
- To conform to the common case, the default role assigned to
parameters of datatypes declared in ``hs-boot`` files is
``representational``. However, if the constructor(s) for the datatype
are given, it makes sense to do normal role inference. This is now
implemented, effectively making the default role for non-abstract
datatypes in ``hs-boot`` files to be ``phantom``, like it is in
regular Haskell code.
- Wildcards can be used in the type arguments of type/data family
instance declarations to indicate that the name of a type variable
doesn't matter. They will be replaced with new unique type variables.
See :ref:`data-instance-declarations` for more details.
- GHC now allows to declare type families as injective. Injectivity
information can then be used by the typechecker. See
:ref:`injective-ty-fams` for details.
- Due to a :ghc-ticket:`security issue <10826>`, Safe Haskell now forbids
annotations in programs marked as :ghc-flag:`-XSafe`.
- Generic instances can be derived for data types whose constructors have
arguments with certain unlifted types. See :ref:`generic-programming` for
more details.
- GHC generics can now provide strictness information for fields in a data
constructor via the ``Selector`` type class.
- The :ghc-flag:`-XDeriveAnyClass` extension now fills in associated type family
default instances when deriving a class that contains them.
- Users can now define record pattern synonyms. This allows pattern synonyms
to behave more like normal data constructors. For example, ::
pattern P :: a -> b -> (a, b)
pattern P{x,y} = (x,y)
will allow ``P`` to be used like a record data constructor and also defines
selector functions ``x :: (a, b) -> a`` and ``y :: (a, b) -> b``.
- Pattern synonyms can now be bundled with type constructors. For a pattern
synonym ``P`` and a type constructor ``T``, ``P`` can be bundled with ``T``
so that when ``T`` is imported ``P`` is also imported. With this change
a library author can provide either real data constructors or pattern
synonyms in an opaque manner. See :ref:`pattern-synonyms` for details. ::
-- Foo.hs
module Foo ( T(P) ) where
data T = T
pattern P = T
-- Baz.hs
module Baz where
-- P is imported
import Foo (T(..))
- Whenever a data instance is exported, the corresponding data family
is exported, too. This allows one to write ::
-- Foo.hs
module Foo where
data family T a
-- Bar.hs
module Bar where
import Foo
data instance T Int = MkT
-- Baz.hs
module Baz where
import Bar (T(MkT))
In previous versions of GHC, this required a workaround via an
explicit export list in ``Bar``.
Compiler
~~~~~~~~
- Warnings can now be controlled with ``-W(no-)...`` flags in addition to
the old ``-f(no-)warn...`` ones. This was done as the first part of a
rewrite of the warning system to provide better control over warnings,
better warning messages, and more common syntax compared to other
compilers. The old ``-f``-based warning flags will remain functional for
the forseeable future.
- Added the option :ghc-flag:`-dth-dec-file`. This dumps out a .th.hs file of
all Template Haskell declarations in a corresponding .hs file. The
idea is that application developers can check this into their
repository so that they can grep for identifiers used elsewhere that
were defined in Template Haskell. This is similar to using
:ghc-flag:`-ddump-to-file` with :ghc-flag:`-ddump-splices` but it always generates a
file instead of being coupled to :ghc-flag:`-ddump-to-file` and only outputs
code that does not exist in the .hs file and a comment for the splice
location in the original file.
- Added the option :ghc-flag:`-fprint-expanded-types`. When enabled, GHC also
prints type-synonym-expanded types in type errors.
- Added the option :ghc-flag:`-fcpr-anal`. When enabled, the demand analyser
performs CPR analysis. It is implied by :ghc-flag:`-O`. Consequently,
:ghc-flag:`-fcpr-off` is now removed, run with :ghc-flag:`-fno-cpr-anal` to get the
old :ghc-flag:`-fcpr-off` behaviour.
- Added the option :ghc-flag:`-fworker-wrapper`. When enabled, the worker-wrapper
transformation is performed after a strictness analysis pass. It is implied
by :ghc-flag:`-O` and by :ghc-flag:`-fstrictness`. It is disabled by :ghc-flag:`-fno-strictness`.
Enabling :ghc-flag:`-fworker-wrapper` while strictness analysis is disabled (by
:ghc-flag:`-fno-strictness`) has no effect.
- Added the options :ghc-flag:`-Wmissed-specialisations` and
:ghc-flag:`-Wall-missed-specialisations`. When enabled, the simplifier will
produce a warning when a overloaded imported function cannot be
specialised (typically due to a missing ``INLINEABLE`` pragma). This
is intended to alert users to cases where they apply ``INLINEABLE`` but
may not get the speed-up they expect.
- Added the option :ghc-flag:`-Wnoncanonical-monad-instances` which helps
detect noncanonical ``Applicative``/``Monad`` instance definitions.
See flag description in :ref:`options-sanity` for more details.
- When printing an out-of-scope error message, GHC will give helpful advice if
the error might be caused by too restrictive imports.
- Added the :ghc-flag:`-Wcompat` warning group, along with its opposite
:ghc-flag:`-Wno-compat`. Turns on warnings that will be enabled by default in the
future, but remain off in normal compilations for the time being. This
allows library authors eager to make their code future compatible to adapt
to new features before they even generate warnings.
- Added the :ghc-flag:`-Wmissing-monadfail-instance` flag. When enabled, this
will issue a warning if a failable pattern is used in a context that does
not have a ``MonadFail`` constraint. This flag represents phase 1 of the
`MonadFail Proposal (MFP)
`__.
- Added the :ghc-flag:`-Wsemigroup` flag. When enabled, this
will issue a warning if a type is an instance of ``Monoid`` but not
``Semigroup``, and when a custom definition ``(<>)`` is made. Fixing these
warnings makes sure the definition of ``Semigroup`` as a superclass of
``Monoid`` does not break any code.
- Added the :ghc-flag:`-Wmissing-pat-syn-sigs` flag. When enabled, this will issue
a warning when a pattern synonym definition doesn't have a type signature.
It is turned off by default but enabled by :ghc-flag:`-Wall`.
- Changed the :ghc-flag:`-fwarn-unused-matches` flag to report unused type variables
in data and type families in addition to its previous behaviour.
To avoid warnings, unused type variables should be prefixed or replaced with
underscores.
- Added the :ghc-flag:`-Wtoo-many-guards` flag. When enabled, this will issue a
warning if a pattern match contains too many guards (over 20 at the
moment). Makes a difference only if pattern match checking is also enabled.
- Added the :ghc-flag:`-ffull-guard-reasoning` flag. When enabled, pattern match
checking tries its best to reason about guards. Since the additional
expressivity may come with a high price in terms of compilation time and
memory consumption, it is turned off by default.
GHCi
~~~~
- ``Main`` with an explicit module header but without ``main`` is now
an error (:ghc-ticket:`7765`).
- The :ghci-cmd:`:back` and :ghci-cmd:`:forward` commands now take an optional count
allowing the user to move forward or backward in history several
steps at a time.
- Added commands :ghci-cmd:`:load! <:load>` and :ghci-cmd:`:reload! <:reload>`,
effectively setting :ghc-flag:`-fdefer-type-errors` before loading a module and
unsetting it after loading if it has not been set before (:ghc-ticket:`8353`).
- ``ghci -e`` now behaves like :ghc-flag:`ghc -e <-e>` (:ghc-ticket:`9360`).
- Added support for top-level function declarations (:ghc-ticket:`7253`).
- The new commands :ghci-cmd:`:all-types`, :ghci-cmd:`:loc-at`, :ghci-cmd:`:type-at`, and
:ghci-cmd:`:uses` designed for editor-integration
(such as Emacs' ``haskell-mode``) originally premiered by ``ghci-ng``
have been integrated into GHCi (:ghc-ticket:`10874`).
- GHCi now supports decoupled operation between the interpreter and the
shell. While this is largely an implementation detail, it opens up a few
interesting possibilities in the future. See :ghc-wiki:`RemoteGHCi` for
details.
Template Haskell
~~~~~~~~~~~~~~~~
- The new :ghc-flag:`-XTemplateHaskellQuotes` flag allows to use the
quotes (not quasi-quotes) subset of ``TemplateHaskell``. This is
particularly useful for use with a stage 1 compiler (i.e. GHC
without interpreter support). Also, :ghc-flag:`-XTemplateHaskellQuotes` is
considered safe under Safe Haskell.
- The ``__GLASGOW_HASKELL_TH__`` CPP constant denoting support for
:ghc-flag:`-XTemplateHaskell` introduced in GHC 7.10.1 has been changed to
use the values ``1``/``0`` instead of the previous ``YES``/``NO``
values.
- Partial type signatures can now be used in splices, see
:ref:`pts-where`.
- Template Haskell now fully supports typed holes and quoting unbound
variables. This means it is now possible to use pattern splices nested
inside quotation brackets.
- Template Haskell now supports the use of ``UInfixT`` in types to
resolve infix operator fixities, in the same vein as ``UInfixP`` and
``UInfixE`` in patterns and expressions. ``ParensT`` and ``InfixT``
have also been introduced, serving the same functions as their
pattern and expression counterparts.
- Template Haskell has now explicit support for representing GADTs. Until
now GADTs were encoded using ``NormalC``, ``RecC`` (record syntax) and
``ForallC`` constructors. Two new constructors - ``GadtC`` and ``RecGadtC`` -
are now supported during quoting, splicing and reification.
- Primitive chars (e.g., ``[| 'a'# |]``) and primitive strings (e.g.,
``[| "abc"# |]``) can now be quoted with Template Haskell. The
``Lit`` data type also has a new constructor, ``CharPrimL``, for
primitive char literals.
- ``addTopDecls`` now accepts annotation pragmas.
- Internally, the implementation of quasi-quotes has been unified with
that of normal Template Haskell splices. Under the previous
implementation, top-level declaration quasi-quotes did not cause a
break in the declaration groups, unlike splices of the form
``$(...)``. This behavior has been preserved under the new
implementation, and is now recognized and documented in
:ref:`th-syntax`.
- The ``Lift`` class is now derivable via the :ghc-flag:`-XDeriveLift` extension. See
:ref:`deriving-lift` for more information.
- The ``FamilyD`` data constructor and ``FamFlavour`` data type have
been removed. Data families are now represented by ``DataFamilyD`` and
open type families are now represented by ``OpenTypeFamilyD`` instead
of ``FamilyD``. Common elements of ``OpenTypeFamilyD`` and
``ClosedTypeFamilyD`` have been moved to ``TypeFamilyHead``.
- The representation of ``data``, ``newtype``, ``data instance``, and
``newtype instance`` declarations has been changed to allow for
multi-parameter type classes in the ``deriving`` clause. In particular,
``dataD`` and ``newtypeD`` now take a ``CxtQ`` instead of a ``[Name]``
for the list of derived classes.
- ``isExtEnabled`` can now be used to determine whether a language extension
is enabled in the ``Q`` monad. Similarly, ``extsEnabled`` can be used to list
all enabled language extensions.
- One can now reify the strictness information of a constructors' fields using
Template Haskell's ``reifyConStrictness`` function, which takes into account
whether flags such as :ghc-flag:`-XStrictData` or
:ghc-flag:`-funbox-strict-fields` are enabled.
Runtime system
~~~~~~~~~~~~~~
- Support for performance monitoring with PAPI has been dropped.
- :rts-flag:`-maxN⟨x⟩ <-maxN>` flag added to complement :rts-flag:`-N`. It will
choose to use at most ⟨x⟩ capabilities, limited by the number of processors
as :rts-flag:`-N` is.
Build system
~~~~~~~~~~~~
- TODO FIXME.
Package system
~~~~~~~~~~~~~~
- TODO FIXME.
hsc2hs
~~~~~~
- :command:`hsc2hs` now supports the ``#alignment`` macro, which can be used to
calculate the alignment of a struct in bytes. Previously, ``#alignment``
had to be implemented manually via a ``#let`` directive, e.g., ::
#let alignment t = "%lu", (unsigned long)offsetof(struct {char x__; t (y__); }, y__)
As a result, if you have the above directive in your code, it will now emit
a warning when compiled with GHC 8.0.
.. code-block:: none
Module.hsc:24:0: warning: "hsc_alignment" redefined [enabled by default]
In file included from dist/build/Module_hsc_make.c:1:0:
/path/to/ghc/lib/template-hsc.h:88:0: note: this is the location of the previous definition
#define hsc_alignment(t...) \
^
To make your code free of warnings on GHC 8.0 and still support earlier
versions, surround the directive with a pragma checking for the right GHC
version. ::
#if __GLASGOW_HASKELL__ < 800
#let alignment t = "%lu", (unsigned long)offsetof(struct {char x__; t (y__); }, y__)
#endif
Libraries
---------
array
~~~~~
- Version number XXXXX (was 0.5.0.0)
.. _lib-base:
base
~~~~
See ``changelog.md`` in the ``base`` package for full release notes.
- Version number 4.9.0.0 (was 4.7.0.0)
- :base-ref:`GHC.Stack ` exports two new types ``SrcLoc`` and ``CallStack``. A
``SrcLoc`` contains package, module, and file names, as well as start
and end positions. A ``CallStack`` is essentially a ``[(String, SrcLoc)]``,
sorted by most-recent call.
- ``error`` and ``undefined`` will now report a partial stack-trace
using the new ``CallStack`` feature (and the :ghc-flag:`-prof` stack if
available).
- A new function, ``interruptible``, was added to ``GHC.IO`` allowing
an ``IO`` action to be run such that it can be interrupted by an
asynchronous exception, even if exceptions are masked (except if
masked with ``interruptibleMask``).
This was introduced to fix the behavior of ``allowInterrupt``, which
would previously incorrectly allow exceptions in uninterruptible
regions (see :ghc-ticket:`9516`).
- Per-thread allocation counters (``setAllocationCounter`` and
``getAllocationCounter``) and limits (``enableAllocationLimit``,
``disableAllocationLimit`` are now available from ``System.Mem``. Previously
this functionality was only available from :base-ref:`GHC.Conc `.
- ``forever``, ``filterM``, ``mapAndUnzipM``, ``zipWithM``, ``zipWithM_``,
``replicateM``, and ``replicateM`` were generalized from ``Monad`` to
``Applicative``. If this causes performance regressions, try to make the
implementation of ``(*>)`` match that of ``(>>)``.
- Add ``URec``, ``UAddr``, ``UChar``, ``UDouble``, ``UFloat``, ``UInt``, and ``UWord`` to
:base-ref:`GHC.Generics ` as part of making GHC generics
capable of handling unlifted types (:ghc-ticket:`10868`)
- Expand ``Floating`` class to include operations that allow for better
precision: ``log1p``, ``expm1``, ``log1pexp`` and ``log1mexp``. These are not
available from ``Prelude``, but the full class is exported from ``Numeric``.
- Add ``Data.List.NonEmpty`` and ``Data.Semigroup`` (to become
super-class of ``Monoid`` in the future). These modules were
provided by the ``semigroups`` package previously. (:ghc-ticket:`10365`)
- The constraints of various functions in ``Control.Monad`` have been
generalized from ``Monad`` to ``Applicative`` including ``filterM``,
``zipWithM`` and ``replicateM_`` (see :ghc-ticket:`10168`).
- Add ``GHC.TypeLits.TypeError`` and ``ErrorMessage`` to allow users
to define custom compile-time error messages. (see :ref:`custom-errors` and
the original :ghc-wiki:`proposal `).
- The ``Generic`` instance for ``Proxy`` is now poly-kinded (see :ghc-ticket:`10775`)
- The ``IsString`` instance for ``[Char]`` has been modified to eliminate
ambiguity arising from overloaded strings and functions like ``(++)``.
- Move ``Const`` from ``Control.Applicative`` to its own module in
``Data.Functor.Const``. (see :ghc-ticket:`11135`)
- Enable ``PolyKinds`` in the ``Data.Functor.Const`` module to give ``Const``
the kind ``* -> k -> *`` (see :ghc-ticket:`10039`).
binary
~~~~~~
- Version number XXXXX (was 0.7.1.0)
bytestring
~~~~~~~~~~
- Version number XXXXX (was 0.10.4.0)
Cabal
~~~~~
- Version number XXXXX (was 1.18.1.3)
containers
~~~~~~~~~~
- Version number XXXXX (was 0.5.4.0)
deepseq
~~~~~~~
- Version number XXXXX (was 1.3.0.2)
directory
~~~~~~~~~
- Version number XXXXX (was 1.2.0.2)
filepath
~~~~~~~~
- Version number XXXXX (was 1.3.0.2)
ghc
~~~
- TODO FIXME.
- The ``HsBang`` type has been removed in favour of ``HsSrcBang`` and
``HsImplBang``. Data constructors now always carry around their
strictness annotations as the user wrote them, whether from an
imported module or not.
- Moved ``startsVarSym``, ``startsVarId``, ``startsConSym``, ``startsConId``,
``startsVarSymASCII``, and ``isVarSymChar`` from ``Lexeme`` to the
``GHC.Lemexe`` module of the ``ghc-boot`` library.
- Add ``isImport``, ``isDecl``, and ``isStmt`` functions.
ghc-boot
~~~~~~~~
- This is an internal package. Use with caution.
- This package was renamed from ``bin-package-db`` to reflect its new purpose
of containing intra-GHC functionality that needs to be shared across
multiple GHC boot libraries.
- Added ``GHC.Lexeme``, which contains functions for determining if a
character can be the first letter of a variable or data constructor in
Haskell, as defined by GHC. (These functions were moved from ``Lexeme``
in ``ghc``.)
- Added ``GHC.LanguageExtensions`` which contains a type listing all
supported language extensions.
ghc-prim
~~~~~~~~
- Version number XXXXX (was 0.3.1.0)
haskell98
~~~~~~~~~
- Version number XXXXX (was 2.0.0.3)
haskell2010
~~~~~~~~~~~
- Version number XXXXX (was 1.1.1.1)
hoopl
~~~~~
- Version number XXXXX (was 3.10.0.0)
hpc
~~~
- Version number XXXXX (was 0.6.0.1)
integer-gmp
~~~~~~~~~~~
- Version number XXXXX (was 0.5.1.0)
old-locale
~~~~~~~~~~
- Version number XXXXX (was 1.0.0.6)
old-time
~~~~~~~~
- Version number XXXXX (was 1.1.0.2)
process
~~~~~~~
- Version number XXXXX (was 1.2.0.0)
template-haskell
~~~~~~~~~~~~~~~~
- Version number XXXXX (was 2.9.0.0)
- The ``Lift`` type class for lifting values into Template Haskell
splices now has a default signature ``lift :: Data a => a -> Q Exp``,
which means that you do not have to provide an explicit
implementation of ``lift`` for types which have a ``Data`` instance.
To manually use this default implementation, you can use the
``liftData`` function which is now exported from
``Language.Haskell.TH.Syntax``.
- ``Info``'s constructors no longer have ``Fixity`` fields. A
``qReifyFixity`` function was added to the ``Quasi`` type class (as
well as the ``reifyFixity`` function, specialized for ``Q``) to allow
lookup of fixity information for any given ``Name``.
time
~~~~
- Version number XXXXX (was 1.4.1)
unix
~~~~
- Version number XXXXX (was 2.7.0.0)
Win32
~~~~~
- Version number XXXXX (was 2.3.0.1)
Known bugs
----------
- TODO FIXME