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.. _release-8-12-1:
Version 8.12.1
==============
The significant changes to the various parts of the compiler are listed in the
following sections.
Highlights
----------
- TODO
Full details
------------
Language
~~~~~~~~
* Record field selectors are now given type signatures that preserve the
user-written order of quantified type variables. Moreover, field selector
type signatures no longer make inferred type variables avaiable for explicit
type application. See :ref:`field-selectors-and-type-applications` for more
details.
In certain situations, this will constitute a breaking change as this can
affect :extension:`TypeApplications`. For instance, given the following
definitions: ::
{-# LANGUAGE PolyKinds #-}
newtype P a = MkP { unP :: Proxy a }
newtype N :: Type -> Type -> Type where
MkN :: forall b a. { unN :: Either a b } -> N a b
Previous versions of GHC would give the following types to ``unP`` and
``unN``: ::
unP :: forall k (a :: k). P a -> Proxy a
unN :: forall a b. N a b -> Either a b
GHC will now give them the following types instead: ::
unP :: forall {k} (a :: k). P a -> Proxy a
unN :: forall b a. N a b -> Either a b
* In obscure scenarios, GHC now rejects programs it previously accepted, but
with unhelpful types. For example, if (with ``-XPartialTypeSignatures``) you
were to write ``x :: forall (f :: forall a (b :: a -> Type). b _). f _``, GHC previously
would have accepted ``x``, but its type would have involved the mysterious ``Any``
internal type family. Now, GHC rejects, explaining the situation.
* GHC now more faithfully implements the instance-lookup scheme described with
:extension:`QuantifiedConstraints`. Previous bugs meant that programs like this
were accepted::
data T (c :: Type -> Constraint)
instance (forall h. c h => Functor h) => Functor (T c)
instance (forall h. c h => Applicative h) => Applicative (T c)
Note that in the instance declaration for ``Applicative (T c)``, we cannot prove
``Functor (T c)``, because the quantified constraint shadows the global instance.
There is an easy workaround, though: just include ``Functor (T c)`` as an assumption. ::
instance (forall h. c h => Applicative h, Functor (T c)) => Applicative (T c)
There is a chance we will tweak the lookup scheme in the future, to make this
workaround unnecessary.
Compiler
~~~~~~~~
GHCi
~~~~
Runtime system
~~~~~~~~~~~~~~
Template Haskell
~~~~~~~~~~~~~~~~
- Implement the Overloaded Quotations proposal (#246). The type of all quotation
forms have now been generalised in terms of a minimal interface necessary for the
implementation rather than the overapproximation of the ``Q`` monad.
- Template Haskell quotes now handle fixity declarations in ``let`` and
``where`` bindings properly. Previously, such fixity declarations would
be dropped when quoted due to a Template Haskell bug.
- The ``-XTemplateHaskellQuotes`` extension now allows nested splices as nested
splices do not lead directly to compile-time evaluation. (!2288)
``ghc-prim`` library
~~~~~~~~~~~~~~~~~~~~
``ghc`` library
~~~~~~~~~~~~~~~
- The type of the ``getAnnotations`` function has changed to better reflect
the fact that it returns two different kinds of annotations, those on
names and those on modules: ::
getAnnotations :: Typeable a
=> ([Word8] -> a) -> ModGuts
-> CoreM (ModuleEnv [a], NameEnv [a])
- The meaning of the ``hs_fixds`` field of ``HsGroup`` has changed slightly.
It now only contains fixity signatures defined for top-level declarations
and class methods defined *outside* of the class itself. Previously,
``hs_fixds`` would also contain fixity signatures for class methods defined
*inside* the class, such as the fixity signature for ``m`` in the following
example: ::
class C a where
infixl 4 `m`
m :: a -> a -> a
If you wish to attain the previous behavior of ``hs_fixds``, use the new
``hsGroupTopLevelFixitySigs`` function, which collects all top-level fixity
signatures, including those for class methods defined inside classes.
``base`` library
~~~~~~~~~~~~~~~~
Build system
~~~~~~~~~~~~
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/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 ``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/libiserv/libiserv.cabal: Internal compiler 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
|
