.. _release-8-4-1: .. Release notes for version 8.4.1 =============================== バージョン 8.4.1 のリリースノート ================================= .. 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 8.2.1 release. コンパイラのさまざまな部分での重要な変更は以降の節で一覧表にしてあります． 8.2.1 リリースに対して大量のバグ修正と性能改善を行いました． .. .. note:: This compiling this release requires GCC 4.7 or newer due to :ghc-ticket:`14244`. .. note:: このバージョンのリリースをコンパイルするには GCC 4.7 以降が必要です． :ghc-ticket:`14244` 参照 .. Highlights ---------- ハイライト ---------- .. The highlights, since the 8.2.1 release, are: - GHC is now capable of deriving more instances - More refinement of the :ghc-flag:`-XTypeInType` story and improvements in type error messages. - Further improvements in code generation - Incorporation of library changes including the Phase 2 of the Semigroup-Monoid Proposal - A variety of Windows compatibility improvements - Many, many bug fixes. 8.2.1 リリースからの変更のハイライトは以下のとおりです． - GHC はより多くのインスタンスを導出できるようなりました． - :ghc-flag:`-XTypeInType` の手順を改良し型エラーのメッセージを改善しました．. - コード生成をさらに改善しました． - Semigroup-Monoid提案のフェーズ2を含むライブラリ変更を行いました． - さまざまな Windows 互換性を改善しました． - 大量のバグを修正しました． .. Full details ------------ 詳細 ---- .. Language ~~~~~~~~ 言語 ~~~~ .. - Data families have been generalised a bit: a data family declaration can now end with a kind variable ``k`` instead of ``Type``. Additionally, data/newtype instance no longer need to list all the patterns of the family if they don't wish to; this is quite like how regular datatypes with a kind signature can omit some type variables. - データ族は少し一般化されました． データ族宣言では， ``Type`` ではなくカインド変数 ``k`` で終端できます． さらに，data/newtype のインスタンスは，不要であれば，その族のすべてのパターンを並べなくてもよくなりました． これは，カインドシグネチャを持つ通常のデータ型ではいくつかの型変数を省略できるのと同じことです． .. - There are now fewer restrictions regarding whether kind variables can appear on the right-hand sides of type and data family instances. Before, there was a strict requirements that all kind variables on the RHS had to be explicitly bound by type patterns on the LHS. Now, kind variables can be *implicitly* bound, which allows constructions like these: :: data family Nat :: k -> k -> * -- k is implicitly bound by an invisible kind pattern newtype instance Nat :: (k -> *) -> (k -> *) -> * where Nat :: (forall xx. f xx -> g xx) -> Nat f g class Funct f where type Codomain f :: * instance Funct ('KProxy :: KProxy o) where -- o is implicitly bound by the kind signature -- of the LHS type pattern ('KProxy) type Codomain 'KProxy = NatTr (Proxy :: o -> *) - カインド変数がデータ族あるいは型族のインスタンスの右辺に現れるかどうかに関する制限はほとんどなくなりました． 以前は，右辺にあるすべてのカインド変数が左辺の型パターンによって明示的に束縛されていなければならないという厳しい要件がありましたが， カインド変数を暗黙に束縛できるようになりました．これにより，次のような構成が可能になります。 :: data family Nat :: k -> k -> * -- k is implicitly bound by an invisible kind pattern newtype instance Nat :: (k -> *) -> (k -> *) -> * where Nat :: (forall xx. f xx -> g xx) -> Nat f g class Funct f where type Codomain f :: * instance Funct ('KProxy :: KProxy o) where -- o is implicitly bound by the kind signature -- of the LHS type pattern ('KProxy) type Codomain 'KProxy = NatTr (Proxy :: o -> *) .. - Implicitly bidirectional pattern synonyms no longer allow bang patterns (``!``) or irrefutable patterns (``~``) on the right-hand side. Previously, this was allowed, although the bang patterns and irrefutable patterns would be silently ignored when used in an expression context. This is now a proper error, and explicitly bidirectional pattern synonyms should be used in their stead. That is, instead of using this (which is an error): :: data StrictJust a = Just !a Use this: :: data StrictJust a <- Just !a where StrictJust !a = Just a - 暗黙に双方向のパターンシノニムは，右辺では，バンパターン(``!``)あるいは反駁可能なパターン(``~``)を使えなくなりました． 以前は使えていましたが，式コンテキストで使用すると，バンパターンと不可反駁パターンは暗黙のうちに無視されていました． これは今や適切にエラーになります． 代わりに明示的に双方向のパターンシノニムを使うべきです． すなわち，エラーになるような :: data StrictJust a = Just !a は使わず．以下のように :: data StrictJust a <- Just !a where StrictJust !a = Just a を使うべきです． .. - GADTs with kind-polymorphic type arguments now require :ghc-flag:`-XTypeInType`. For instance, consider the following, :: data G :: k -> * where GInt :: G Int GMaybe :: G Maybe In previous releases this would compile with :ghc-flag:`-XPolyKinds` alone due to bug :ghc-ticket:`13391`. As of GHC 8.4, however, this requires :ghc-flag:`-XTypeInType`. Note that since GADT kind signatures aren't generalized, this will also require that you provide a :ref:`CUSK ` by explicitly quantifying over the kind argument, ``k``, :: data G :: forall k. k -> * where GInt :: G Int GMaybe :: G Maybe - カインド多相の型引数をもつ GADT を扱うには :ghc-flag:`-XTypeInType` が有効でなければなりません． たとえいば，以下の :: data G :: k -> * where GInt :: G Int GMaybe :: G Maybe の宣言を考えましょう． 一つ前のリリースでは，:ghc-flag:`-XPolyKinds` だけを有効にすれば，コンパイルできましたが，これはバグ :ghc-ticket:`13391` でした． しかしながら，GHC 8.4 では， :ghc-flag:`-XTypeInType` が必要です． GADT のカインドシグネチャは一般化されていませんので，カインド引数 ``k`` を 明示的に限量化して， :ref:`CUSK ` を提供する必要があります． :: data G :: forall k. k -> * where GInt :: G Int GMaybe :: G Maybe .. - The order in which type variables are quantified in GADT constructor type signatures has changed. Before, if you had ``MkT`` as below: :: data T a where MkT :: forall b a. b -> T a Then the type of ``MkT`` would (counterintuitively) be ``forall a b. b -> T a``! Now, GHC quantifies the type variables in the order that the users writes them, so the type of ``MkT`` is now ``forall b a. b -> T a`` (this matters for :ghc-flag:`-XTypeApplications`). - GADT 構成子の型シグネチャで型変数が限量化される順番が変更になりました． 以前は，以下のように ``MkT`` を書いたとすれば :: data T a where MkT :: forall b a. b -> T a ``MkT`` の型は直感に反して ``forall a b. b -> T a`` でした． GHC は型変数をユーザが書いた順序で限量化するようになったので， ``MkT`` の型は， ``forall b a. b -> T a`` です(:ghc-flag:`-XTypeApplications`の場合)． .. - The new :ghc-flag:`-XEmptyDataDeriving` extension allows deriving ``Eq``, ``Ord``, ``Read``, and ``Show`` instances directly for empty data types, as in ``data Empty deriving Eq``. (Previously, this would require the use of :ghc-flag:`-XStandaloneDeriving` to accomplish.) One can also now derive ``Data`` instances directly for empty data types (as in ``data Empty deriving Data``) without needing to use :ghc-flag:`-XStandaloneDeriving`. However, since already requires a GHC extension (:ghc-flag:`-XDeriveDataTypeable`), one does not need to enable :ghc-flag:`-XEmptyDataDeriving` to do so. This also goes for other classes which require extensions to derive, such as :ghc-flag:`-XDeriveFunctor`. - 新たに追加された :ghc-flag:`-XEmptyDataDeriving` 拡張により，空のデータ型に対する ``Eq`` ， ``Ord`` ， ``Read`` ， ``Show`` のインスタンスを ``data Empty deriving Eq`` のように 直接導出できるようになりました． (以前は :ghc-flag:`-XStandaloneDeriving` を有効にしなければなりませんでした．) また :ghc-flag:`-XStandaloneDeriving` を使わなくても，空のデータ型に対して ``Data`` インスタンスを (``data Empty deriving Data`` のように)直接導出できるようになりました． とはいえ，この導出には :ghc-flag:`-XDeriveDataTypeable` という GHC拡張が必要であり，それが有効になっていれば， あらためて :ghc-flag:`-XEmptyDataDeriving` を有効しなくてもすみます． 同じことが :ghc-flag:`-XDeriveFunctor` などの拡張を必要する他の型クラスについてもいえます． .. - Hexadecimal floating point literals (e.g. ``0x0.1p4``), enabled with :ghc-flag:`-XHexFloatLiterals`. See :ref:`Hexadecimal floating point literals ` for the full details. - :ghc-flag:`-XHexFloatLiterals` を有効にすると16進浮動小数点数リテラル(たとえば ``0x0.1p4``)表記が可能になります． 詳細については :ref:`Hexadecimal floating point literals ` を参照してください． Compiler ~~~~~~~~ - LLVM code generator (e.g. :ghc-flag:`-fllvm`) compatible with LLVM releases in the |llvm-version| series. - Add warning flag :ghc-flag:`-Wmissing-export-lists` which causes the type checker to warn when a module does not include an explicit export list. - The ``configure`` script now no longer accepts ``--with-TOOL`` flags (e.g. ``--with-nm``, ``--with-ld``, etc.). Instead, these are taken from environment variables, as is typical in ``autoconf`` scripts. For instance, ``./configure --with-nm=/usr/local/bin/nm`` turns into ``./configure NM=/usr/local/bin/nm``. - Derived ``Functor``, ``Foldable``, and ``Traversable`` instances are now optimized when their last type parameters have phantom roles. Specifically, :: fmap _ = coerce traverse _ x = pure (coerce x) foldMap _ _ = mempty These definitions of ``foldMap`` and ``traverse`` are lazier than the ones we would otherwise derive, as they may produce results without inspecting their arguments at all. See also :ref:`deriving-functor`, :ref:`deriving-foldable`, and :ref:`deriving-traversable`. - Derived instances for empty data types are now substantially different than before. Here is an overview of what has changed. These examples will use a running example of ``data Empty a`` to describe what happens when an instance is derived for ``Empty``: - Derived ``Eq`` and ``Ord`` instances would previously emit code that used ``error``: :: instance Eq (Empty a) where (==) = error "Void ==" instance Ord (Empty a) where compare = error "Void compare" Now, they emit code that uses maximally defined, lazier semantics: :: instance Eq (Empty a) where _ == _ = True instance Ord (Empty a) where compare _ _ = EQ - Derived ``Read`` instances would previous emit code that used ``parens``: :: instance Read (Empty a) where readPrec = parens pfail But ``parens`` forces parts of the parsed string that it doesn't need to. Now, the derived instance will not use ``parens`` (that it, parsing ``Empty`` will always fail, without reading *any* input): :: instance Read (Empty a) where readPrec = pfail - Derived ``Show`` instances would previously emit code that used ``error``: :: instance Show (Empty a) where showsPrec = error "Void showsPrec" Now, they emit code that inspects the argument. That is, if the argument diverges, then showing it will also diverge: :: instance Show (Empty a) where showsPrec _ x = case x of {} - Derived ``Functor``, ``Foldable``, ``Traversable``, ``Generic``, ``Generic1``, ``Lift``, and ``Data`` instances previously emitted code that used ``error``: :: instance Functor Empty where fmap = error "Void fmap" instance Foldable Empty where foldMap = error "Void foldMap" instance Traversable Empty where traverse = error "Void traverse" instance Generic (Empty a) where from = M1 (error "No generic representation for empty datatype Empty") to (M1 _) = error "No values for empty datatype Empty" -- Similarly for Generic1 instance Lift (Empty a) where lift _ = error "Can't lift value of empty datatype Empty" instance Data a => Data (Empty a) where gfoldl _ _ _ = error "Void gfoldl" toConstr _ = error "Void toConstr" ... Now, derived ``Functor``, ``Traversable, ``Generic``, ``Generic1``, ``Lift``, and ``Data`` instances emit code which inspects their arguments: :: instance Functor Empty where fmap _ x = case x of {} instance Traversable Empty where traverse _ x = pure (case x of {}) instance Generic (Empty a) where from x = M1 (case x of {}) to (M1 x) = case x of {} -- Similarly for Generic1 instance Lift (Empty a) where lift x = pure (case x of {}) instance Data a => Data (Empty a) where gfoldl _ x = case x of {} toConstr x = case x of {} ... Derived ``Foldable`` instances now are maximally lazy: :: instance Foldable Empty where foldMap _ _ = mempty - Derived ``Foldable`` instances now derive custom definitions for ``null`` instead of using the default one. This leads to asymptotically better performance for recursive types not shaped like cons-lists, and allows ``null`` to terminate for more (but not all) infinitely large structures. - Configure on Windows now supports the ``--enable-distro-toolchain`` ``configure`` flag, which can be used to build a GHC using compilers on your ``PATH`` instead of using the bundled bindist. See :ghc-ticket:`13792` - GHC now enables :ghc-flag:`-fllvm-pass-vectors-in-regs` by default. This means that GHC will now use native vector registers to pass vector arguments across function calls. - The optional ``instance`` keyword is now usable in type family instance declarations. See :ghc-ticket:`13747` - Lots of other bugs. See `Trac `_ for a complete list. - New flags :ghc-flag:`-fignore-optim-changes` and :ghc-flag:`-fignore-hpc-changes` allow GHC to reuse previously compiled modules even if they were compiled with different optimisation or HPC flags. These options are enabled by default by :ghc-flag:`--interactive`. See :ghc-ticket:`13604` Runtime system ~~~~~~~~~~~~~~ - Function ``hs_add_root()`` was removed. It was a no-op since GHC-7.2.1 where module initialisation stopped requiring a call to ``hs_add_root()``. - Proper import library support added to GHC which can handle all of the libraries produced by ``dlltool``. The limitation of them needing to be named with the suffix ``.dll.a`` is also removed. See :ghc-ticket:`13606`, :ghc-ticket:`12499`, :ghc-ticket:`12498` - The GHCi runtime linker on Windows now supports the ``big-obj`` file format. - The runtime system's :ref:`native stack backtrace ` support on POSIX platforms is now triggered by ``SIGQUIT`` instead of ``SIGUSR2`` as it was in previous releases. This change is to bring GHC's behavior into compliance with the model set by the most Java virtual machine implementations. - The GHC runtime on Windows now uses Continue handlers instead of Vectorized handlers to trap exceptions. This change gives other exception handlers a chance to handle the exception before the runtime does. Furthermore The RTS flag :rts-flag:`--install-seh-handlers=` Can be used on Wndows to completely disable the runtime's handling of exceptions. See :ghc-ticket:`13911`, :ghc-ticket:`12110`. - The GHC runtime on Windows can now generate crash dumps on unhandled exceptions using the RTS flag :rts-flag:`--generate-crash-dumps`. - The GHCi runtime linker now avoid calling GCC to find libraries as much as possible by caching the list of search directories of GCC and querying the file system directly. This results in much better performance, especially on Windows. - The GHC runtime on Windows can now generate stack traces on unhandled exceptions. When running in GHCi more information is displayed about the symbols if available. This behavior can be controlled with the RTS flag `--generate-stack-traces=`. Template Haskell ~~~~~~~~~~~~~~~~ - Template Haskell now reifies data types with GADT syntax accurately. Previously, TH used heuristics to determine whether a data type should be reified using GADT syntax, which could lead to incorrect results, such as ``data T1 a = (a ~ Int) => MkT1`` being reified as a GADT and ``data T2 a where MkT2 :: Show a => T2 a`` *not* being reified as a GADT. In addition, reified GADT constructors now more accurately track the order in which users write type variables. Before, if you reified ``MkT`` as below: :: data T a where MkT :: forall b a. b -> T a Then the reified type signature of ``MkT`` would have been headed by ``ForallC [PlainTV a, PlainTV b]``. Now, reifying ``MkT`` will give a type headed by ``ForallC [PlainTV b, PlainTV a]``, as one would expect. - ``Language.Haskell.TH.FamFlavour``, which was deprecated in GHC 8.2, has been removed. ``base`` library ~~~~~~~~~~~~~~~~ - Blank strings can now be used as values for environment variables using the ``System.Environment.Blank`` module. See :ghc-ticket:`12494` - ``Data.Type.Equality.==`` is now a closed type family. It works for all kinds out of the box. Any modules that previously declared instances of this family will need to remove them. Whereas the previous definition was somewhat ad hoc, the behavior is now completely uniform. As a result, some applications that used to reduce no longer do, and conversely. Most notably, ``(==)`` no longer treats the ``*``, ``j -> k``, or ``()`` kinds specially; equality is tested structurally in all cases. Build system ~~~~~~~~~~~~ - ``dll-split`` has been removed and replaced with an automatic partitioning utility ``gen-dll``. This utility can transparently split and compile any DLLs that require this. Note that the ``rts`` and ``base`` can not be split at this point because of the mutual recursion between ``base`` and ``rts``. There is currently no explicit dependency between the two in the build system and such there is no way to notify ``base`` that the ``rts`` has been split, or vice versa. (see :ghc-ticket:`5987`). 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 Win32 ~~~~~ .. attention:: This release is a backwards incompatible release which corrects the type of certain APIs. See issue `#24 `_.