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 7.4 branch.
The highlights, since the 7.4 branch, are:
Polymorphic kinds and data promotion are now fully implemented and supported features: 7.8. 種多相.
Windows 64bit is now a supported platform.
It is now possible to defer type errors until runtime using the
-fdefer-type-errors flag: 7.13. 型エラーを実行時まで遅らせる.
The RTS now supports changing the number of capabilities at runtime
with Control.Concurrent.setNumCapabilities: 4.15.2. SMP並列性のためのRTSオプション.
There is a new extension ExplicitNamespaces
that allows to qualify the export of a type with the
type keyword.
The behavior of the TypeOperator extension has
changed: previously, only type operators starting with ":" were
considered type constructors, and other operators were treated as
type variables. Now type operators are always constructors.
It is now possible to explicitly annotate types with kind variables (#5862). You can now write, for example:
class Category (c :: k -> k -> *) where type Ob c :: k -> Constraint id :: Ob c a => c a a (.) :: (Ob c a, Ob c b, Ob c c) => c b c -> c a b -> c a c
and the variable k, ranging over kinds, is in scope within the
class declaration.
It is now possible to derive instances of
Generic1 automatically. See 7.22. 総称プログラミング for more information.
There is a new FFI calling convention capi,
enabled by the CApiFFI extension. For example,
given the following declaration:
foreign import capi "header.h f" f :: CInt -> IO CInt
GHC will generate code to call f using the C
API defined in the header header.h. Thus
f can be called even if it may be defined as a
CPP #define, rather than a proper function.
There is a new pragma CTYPE, which can be used
to specify the C type that a Haskell type corresponds to, when it
is used with the capi calling convention.
Generic default methods are now allowed for multi-parameter type classes.
A constructor of a GADT is now considered infix (by a derived
Show instance) if it is a two-argument
operator with a fixity declaration (#5712).
There is a new extension InstanceSigs, which
allows type signatures to be specified in instance declarations.
GHC now supports numeric and string type literals (enabled by
DataKinds), of kind Nat and
Symbol respectively (see 7.9.5. 昇格したリテラル).
The type Any can now be used as an argument
for foreign prim functions.
The mdo keyword has been reintroduced. This
keyword can be used to create do expressions
with recursive bindings. The behavior of the
rec keyword has been changed, so that it does
not perform automatic segmentation in a do
expression anymore.
There is a new syntactic construct (enabled by the LambdaCase extension)
for creating an anonymous function out of a case expression. For example,
the following expression:
\case
Nothing -> 0
Just n -> n
is equivalent to:
\x -> case x of
Nothing -> 0
Just n -> n
See 7.3.15. ラムダcase for more details.
There is a new syntactic construct (enabled by the
MultiWayIf extension) to create conditional
expressions with multiple branches. For example, you can now
write:
if | x == 0 -> [...] | x > 1 -> [...] | x < 0 -> [...] | otherwise -> [...]
See 7.3.16. 多選択肢のif式 for more information.
Some limitations on the usage of unboxed tuples have been lifted.
For example, when the UnboxedTuples extension
is on, an unboxed tuple can now be used as the type of a
constructor, function argument, or variable:
data Foo = Foo (# Int, Int #) f :: (# Int, Int #) -> (# Int, Int #) f x = x g :: (# Int, Int #) -> Int g (# a,b #) = a h x = let y = (# x,x #) in ...
Unboxed tuple can now also be nested:
f :: (# Int, (# Int, Int #), Bool #)
The -package flag now correctly loads only
the most recent version of a package (#7030).
In --make mode, GHC now gives an indication
of why a module is being recompiled.
There is a new flag -freg-liveness flag to control if
STG liveness information is used for optimisation. The flag is
enabled by default.
Package database flags have been renamed from
-package-conf* to
-package-db*.
It is now possible to hide the global package db, and specify the order of the user and global package databases in the stack (see 4.9.4. パッケージデータベース).
Commands defined later have now precedence in the resolution of abbreviated commands (#3858).
It is now possible to specify a custom pretty-printing function
for expressions evaluated at the prompt using the
-interactive-print flag.
GHCi now supports loading additional .ghci
files via the -ghci-script flag (#5265).
A new :seti command has been introduced,
which sets an option that applies only at the prompt.
Files are now reloaded after having been edited with the :edit command.
default declarations can now be entered at the GHCi prompt.
The presentation of parallel GC work balance in +RTS
-s is now expressed as a percentage value (with
100% being "perfect") instead of a number from 1 to N, with N
being the number of capabilities.
The RTS now supports changing the number of capabilities at runtime
with Control.Concurrent.setNumCapabilities: 4.15.2. SMP並列性のためのRTSオプション.
The internal timer is now based on a monotonic clock in both the threaded and non-threaded RTS, on all tier-1 platforms.
GHC >= 7.0 is now required for bootstrapping.
Windows 64bit is now a supported platform.
There have been some changes that have effected multiple libraries:
The deprecated function catch has been
removed from Prelude.
The following libraries have been removed from the GHC tree:
extensible-exceptions
mtl
The following libraries have been added to the GHC tree:
tranformers (version 0.3.0.0)
Version number 0.4.0.1 (was 0.4.0.0)
Version number 4.6.0.0 (was 4.5.1.0)
The Text.Read module now exports functions
readEither :: Read a => String -> Either String a readMaybe :: Read a => String -> Maybe a
An infix alias for mappend in Data.Monoid has been introduced:
(<>) :: Monoid m => m -> m -> m
The Bits class does not have a Num superclass anymore.
You can make code that works with both Haskell98/Haskell2010 and GHC by:
Whenever you make a Bits instance
of a type, also make Num instance, and
Whenever you give a function, instance or class a
Bits t constraint, also give it
a Num t constraint.
Applicative and
Alternative instances for the
ReadP and ReadPrec monads
have been added.
foldl' and foldr' in
Data.Foldable are now methods of the
Foldable class.
The deprecated Control.OldException module has now been removed.
Strict versions of modifyIORef and atomicModifyIORef have been added to the Data.IORef module:
modifyIORef' :: IORef a -> (a -> a) -> IO () atomicModifyIORef' :: IORef a -> (a -> (a,b)) -> IO b
Similarly, a strict version of modifySTRef
has been added to Data.STRef.
A bug in the fingerprint calculation for
TypeRep (#5962)
has been fixed.
A new function lookupEnv has been added to
System.Environment, which behaves like
getEnv, but returns
Nothing when the environment variable is
not defined, instead of throwing an exception.
There is a new function getGCStatsEnabled in
GHC.Stats, which checks whether GC stats
have been enabled (for example, via the -T
RTS flag).
QSem in
Control.Concurrent is now deprecated, and
will be removed in GHC 7.8. Please use an alternative, e.g. the
SafeSemaphore package, instead.
A new function getExecutablePath has been
added to System.Environment. This function
returns the full path of the current executable, as opposed to
getProgName, which only returns the base
name.
The Data.HashTable module is now deprecated,
and will be removed in GHC 7.8. Please use an alternative, e.g.
the hashtables package, instead.
The Data.Ord module now exports the
Down newtype, which
reverses the sort order of its argument.
This is an internal package, and should not be used.
Version number 0.5.1.1 (was 0.5.1.0)
Version number 0.10.0.0 (was 0.9.2.1)
A new module
Data.ByteString.Lazy.Builder has been
added.
The new module defines a Builder monoid,
which allows to efficiently construct bytestrings by
concatenation. Possible applications include binary
serialization, targets for efficient pretty-printers, etc.
Version number 1.16.0 (was 1.14.0)
For details of the changes to the Cabal library, please see the Cabal changelog.
Version number 0.5.0.0 (was 0.4.2.1)
See the announcement for details of the changes to the containers library.
Version number 1.3.0.1 (was 1.3.0.0)
Version number 1.2.0.0 (was 1.1.0.2)
The dependency on the old-time package has been changed to time.
Version number 1.3.0.1 (was 1.3.0.0)
This is an internal package, and should not be used.
Version number 2.0.0.2 (was 2.0.0.1)
Version number 1.1.1.0 (was 1.1.0.1)
Version number 3.9.0.0 (was 3.8.7.3)
Compiler.Hoopl.Block now contains the
Block datatype and all the operations on blocks.
Compiler.Hoopl.Graph now has the
operations on Graphs.
Compiler.Hoopl.Util and
Compiler.Hoopl.GraphUtil have been
removed; their contents have been moved to other modules.
The Dataflow algorithms have been optimized.
Numerous other API changes.
Version number 0.6.0.0 (was 0.5.1.1)
The dependency on the old-time package has been changed to time.
Version number 0.5.0.0 (was 0.4.0.0)
Version number 1.0.0.5 (was 1.0.0.4)
Version number 1.1.0.1 (was 1.1.0.0)
Version number 1.1.0.2 (was 1.1.0.1)
Asynchronous exception bugs in
readProcess and
readProcessWithExitCode have been fixed.
Version number 2.8.0.0 (was 2.7.0.0)
Promoted kinds and kind polymorphism are now supported in Template Haskell.
Fixity declarations have been added to Template Haskell.
The StringPrimL constructor for
Lit now takes a Word8
array, instead of a String.
Version number 1.4.1 (was 1.4)
Version number 2.6.0.0 (was 2.5.1.1)
Bindings for mkdtemp and mkstemps have been added.
New functions setEnvironment and cleanEnv have been added.
Bindings for functions to access high resolution timestamps have been added.
Version number 2.3.0.0 (was 2.2.2.0)