1.7. Release notes for version 7.0.1
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## 1.7. Release notes for version 7.0.1

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 6.12 branch.

### 1.7.1. Highlights

- GHC now defaults to the Haskell 2010 language standard.

  Libraries are not quite so straightforward. By default, GHC provides access to the `base` package, which includes the Haskell 2010 libraries, albeit with a few minor differences. For those who want to write strictly standards-conforming code we also provide the `haskell2010` package which provides the precise APIs specified by Haskell 2010, but because the module names in this package overlap with those in the `base` package it is not possible to use both `haskell2010` and `base` at the same time (this also applies to the `array` package). Hence to use the Haskell 2010 libraries you should hide the `base` and `array` packages, for example with GHCi:

      $ ghci -package haskell2010 -hide-package base -hide-package array

  If you are using Cabal it isn't necessary to hide `base` and `array` explicitly, just don't include them in your `build-depends`.

- The `-fglasgow-exts` flag has been deprecated. Individual extensions should be enabled instead.

  The `GADTs` and `TypeFamilies` exntensions are no longer enabled by `-fglasgow-exts`.

- On POSIX platforms, there is a new I/O manager based on epoll/kqueue/poll, which allows multithreaded I/O code to scale to a much larger number (100k+) of threads.

- GHC now includes an LLVM code generator. For certain code, particularly arithmetic heavy code, using the LLVM code generator can bring some nice performance improvements.

- The type checker has been overhauled, which means it is now able to correctly handle interactions between the type system extensions.

- The inliner has been overhauled, which should in general give better performance while reducing unnecessary code-size explosion.

- Large parts of the runtime system have been overhauled, in particular the machinery related to blocking and wakeup of threads and exception throwing (`throwTo`). Several instances of pathological performance have been fixed, especially where large numbers of threads are involved.

- Due to changes in the runtime system, if you are using `Control.Parallel.Strategies` from the `parallel` package, please upgrade to at least version 2 (preferably version 3). The implementation of Strategies in `parallel-1.x` will lose parallelism with GHC 7.0.1.

- The full Haskell `import` syntax can now been used to bring modules into scope in GHCi, e.g.

      Prelude> import Data.List as L
      Prelude Data.List> L.length "foo"
      3

- GHC now comes with a more recent mingw bundled on Windows, which includes a fix for windres on Windows 7.

- There is a new `-fno-ghci-sandbox` flag, which stops GHCi running computations in a separate thread. In particular, this is useful for GLUT on OS X, which only works if being run on the main thread.

### 1.7.2. Language changes

- GHC now understands the `Haskell98` and `Haskell2010` languages.

  These get processed before the language extension pragmas, and define the default sets of extensions that are enabled. If neither is specified, then the default is `Haskell2010` plus the `MonoPatBinds` extension.

- GHC now supports the `DoAndIfThenElse` extension, which is part of the Haskell 2010 standard.

- Rebinadble syntax now has its own extension, `RebindableSyntax`, and thus is no longer enabled by `NoImplicitPrelude`.

- Datatype contexts, such as the `Eq a` in

      data Eq a => Set a = NilSet | ConsSet a (Set a)

  are now treated as an extension `DatatypeContexts` (on by default) by GHC.

- GHC's support for unicode source has been improved, including removing support for U+22EF for the `..` symbol. See Section 7.3.1, “Unicode syntax” for more details.

- Pragmas are now reread after preprocessing. In particular, this means that if a pragma is used to turn CPP on, then other pragmas can be put in CPP conditionals.

- The `TypeOperators` extension now allows instance heads to use infix syntax.

- The `PackageImports` extension now understands `this` to mean the current package.

- The `INLINE` and `NOINLINE` pragmas can now take a `CONLIKE` modifier, which indicates that the right hand side is cheap to compute, and can thus be duplicated more freely. See Section 7.14.3, “How rules interact with INLINE/NOINLINE and CONLIKE pragmas” for more details.

- A `ForceSpecConstr` annotation on a type, e.g.

      import SpecConstr
      {-# ANN type SPEC ForceSpecConstr #-}

  can be used to force GHC to fully specialise argument of that type.

- A `NoSpecConstr` annotation on a type, e.g.

      import SpecConstr
      {-# ANN type T NoSpecConstr #-}

  can be used to prevent SpecConstr from specialising on arguments of that type.

- There is are two experimental new extensions `AlternativeLayoutRule` and `AlternativeLayoutRuleTransitional`, which are for exploring alternative layout rules in Haskell'. The details are subject to change, so we advise against using them in real code for now.

- The `NewQualifiedOperators` extension has been deprecated, as it was rejected by the Haskell' committee.

### 1.7.3. Warnings

- There is now a warning for missing type signatures for polymorphic local bindings, controlled by the new `-fwarn-missing-local-sigs` flag.

- There is now a warning for missing import lists, controlled by the new `-fwarn-missing-import-lists` flag.

- GHC will now warn about `SPECIALISE` and `UNPACK` pragmas that have no effect.

- The `-fwarn-simple-patterns` flag has been removed. The warnings have been merged into the `-fwarn-incomplete-patterns` flag.

### 1.7.4. DLLs

- Shared libraries are once again supported on Windows.

- Shared libraries are now supported on OS X, both on x86 and on PowerPC. The new `-dylib-install-name` GHC flag is used to set the location of the dynamic library. See Section 4.12.4, “Finding shared libraries at runtime” for more details.

### 1.7.5. Runtime system

- For security reasons, by default, the only RTS flag that programs accept is `+RTS --info`. If you want the full range of RTS flags then you need to link with the new `-rtsopts` flag. See Section 4.11.6, “Options affecting linking” for more details.

- The RTS now exports a function `setKeepCAFs` which is important when loading Haskell DLLs dynamically, as a DLL may refer to CAFs that hae already been GCed.

- The garbage collector no longer allows you to specify a number of steps; there are now always 2. The `-T` RTS flag has thus been removed.

- A new RTS flag `-H` causes the RTS to use a larger nursery, but without exceeding the amount of memory that the application is already using. It makes some programs go slower, but others go faster.

- GHC now returns memory to the OS, if memory usage peaks and then drops again. This is mainly useful for long running processes which normally use very little memory, but occasionally need a lot of memory for a short period of time.

- On OS X, eventLog events are now available as DTrace probes.

- The PAPI support has been improved. The new RTS flag `-a#0x40000000` can be used to tell the RTS to collect the native PAPI event `0x40000000`.

### 1.7.6. Compiler

- GHC now defaults to `--make` mode, i.e. GHC will chase dependencies for you automatically by default.

- GHC now includes an LLVM code generator.

  This includes a number of new flags: a flag to tell GHC to use LLVM, `-fllvm`; a flag to dump the LLVM input ,`-ddump-llvm`; flags to keep the LLVM intermediate files, `-keep-llvm-file` and `-keep-llvm-files`; flags to set the location and options for the LLVM optimiser and compiler, `-pgmlo`, `-pgmlc`, `-optlo` and `-optlc`. The LLVM code generator requires LLVM version 2.7 or later on your path.

- It is now possible to use `-fno-code` with `--make`.

- The new flag `-dsuppress-coercions` controls whether GHC prints coercions in core dumps.

- The new flag `-dsuppress-module-prefixes` controls whether GHC prints module qualification prefixes in core dumps.

- The inliner has been overhauled. The most significant user-visible change is that only saturated functions are inlined, e.g.

      (.) f g x = f (g x)

  would only be inlined if `(.)` is applied to 3 arguments, while

      (.) f g = \x -> f (g x)

  will be inlined if only applied to 2 arguments.

- The `-finline-if-enough-args` flag is no longer supported.

- Column numbers in warnings and error messages now start at 1, as is more standard, rather than 0.

- GHCi now understands most linker scripts. In particular, this means that GHCi is able to load the C pthread library.

- The `ghc --info` output has been updated:

  It now includes the location of the global package database, in the `Global Package DB` field.

  It now includes the build, host and target platforms, in the `Build platform`, `Host platform` and `Target platform` fields.

  It now includes a `Have llvm code generator` field.

  The `Win32 DLLs` field has been removed.

- The registerised via-C backend, and the `-fvia-C` flag, have been deprecated. The poor floating-point performance in the x86 native code generator has now been fixed, so we don't believe there is still any reason to use the via-C backend.

- There is now a new flag `--supported-extensions`, which currently behaves the same as `--supported-languages`.

- GHC progress output such as

      [ 1 of 5] Compiling Foo              ( Foo.hs, Foo.o )

  is now sent to stdout rather than stderr.

- The new flag `-fexpose-all-unfoldings` makes GHC put unfoldings for everything in the interface file.

- There are two new flags, `-fno-specialise` and `-fno-float-in`, for disabling the specialise and float-in passes.

- The new flag `-fstrictness-before=`n`` tells GHC to run an additional strictness analysis pass before simplifier phase `n`.

- There is a new flag `-funfolding-dict-discount` for tweaking the optimiser's behaviour.

- The `-fspec-inline-join-points` flag has been removed.

- The `-dynload wrapper` flag has been removed.

- The `__HASKELL1__`, `__HASKELL98__` and `__CONCURRENT_HASKELL__` symbols are no longer defined by default when CPPing.

### 1.7.7. GHCi

- GHCi now understands layout in multi-line commands, so this now works:

      Prelude> :{
      Prelude| let x = 1
      Prelude|     y = 2 in x + y
      Prelude| :}
      3

### 1.7.8. Template Haskell and Quasi-Quoters

- It is now possible to quasi-quote patterns with `[p| ... |]`.

- It is no longer necessary to use a `$` before the name of a quasi-quoter, e.g. one can now say `[expr| ... |]` rather than `[$expr| ... |]`.

- It is now possible to use a quasi-quoter for types, e.g. `f :: [$qq| ... |]`

- It is now possible to quasi-quote existentials and GADTs.

### 1.7.9. GHC API

- There are now `Data` and `Typeable` instances for the HsSyn typed.

### 1.7.10. Libraries

#### 1.7.10.1. array

- Version number 0.3.0.2 (was 0.3.0.1)

#### 1.7.10.2. base

- Version number 4.3.0.0 (was 4.2.0.2)

- There is a new asynchronous exception control API in `Control.Exception`, using the new functions `mask :: ((forall a. IO a -> IO a) -> IO b) -> IO b` and `mask_ :: IO a -> IO a` rather than the old `block` and `unblock`. There are also functions `uninterruptibleMask :: ((forall a. IO a -> IO a) -> IO b) -> IO b` and `getMaskingState :: IO MaskingState`, and a type `MaskingState`, as well as `forkIOUnmasked :: IO () -> IO ThreadId` in `Control.Concurrent`.

- `Control.Monad` exports a new function `void :: Functor f => f a -> f ()`.

- `Data.Tuple` exports a new function `swap :: (a,b) -> (b,a)`.

- `System.IO` exports a new function `hGetBufSome :: Handle -> Ptr a -> Int -> IO Int` which is like `hGetBuf` but can return short reads.

- There is a new function `mfilter :: MonadPlus m => (a -> Bool) -> m a -> m a` in `Control.Monad`.

- The `Foreign.Marshal` module now exports `unsafeLocalState :: IO a -> a` as specified by Haskell 2010.

- The `` module now exports four new functions specified by Haskell 2010: `castCUCharToChar :: CUChar -> Char`, `castCharToCUChar :: Char -> CUChar`, `castCSCharToChar :: CSChar -> Char` and `castCharToCSChar :: Char -> CSChar`.

- The `Foreign.Marshal.Alloc` module now exports `allocaBytesAligned :: Int -> Int -> (Ptr a -> IO b) -> IO b` for allocating memory with a particular alignment.

- There is a new function `numSparks :: IO Int` in `GHC.Conc`.

- `Data.Either.partitionEithers` in now lazier.

- There is now a `Typeable` instance for `Data.Unique.Unique`.

- `Control.Concurrent.SampleVar.SampleVar` is now an abstract type.

- There are now `Applicative`, `Alternative` and `MonadPlus` instances for `STM`.

- There are now `Applicative`, `Monad` and `MonadFix` instances for `Either`.

- There are now `Ord`, `Read` and `Show` instances for `Newline` and `NewlineMode`.

- There is now a `Show` instance for `TextEncoding`.

- The `unGetChan` and `isEmptyChan` functions in `Control.Concurrent.Chan` are now deprecated. `Control.Concurrent.STM.TChan` should be used instead if you need that functionality.

- The `Read Integer` instance now matches the standard definition.

#### 1.7.10.3. base 3 compat

- We no longer ship a base 3 compat package

#### 1.7.10.4. bin-package-db

- This is an internal package, and should not be used.

#### 1.7.10.5. bytestring

- Version number 0.9.1.8 (was 0.9.1.7)

#### 1.7.10.6. Cabal

- Version number 1.10.0.0 (was 1.8.0.6)

- Many API changes. See the Cabal docs for more information.

#### 1.7.10.7. containers

- Version number 0.4.0.0 (was 0.3.0.0)

- Strictness is now more consistent, with containers being strict in their elements even in singleton cases.

- There is a new function `insertLookupWithKey'` in `Data.Map`.

- The `foldWithKey` function in `Data.Map` has been deprecated in favour of `foldrWithKey`.

#### 1.7.10.8. directory

- Version number 1.1.0.0 (was 1.0.1.1)

- The `System.Directory` module now exports the `Permissions` type abstractly. There are also new functions `setOwnerReadable`, `setOwnerWritable`, `setOwnerExecutable` and `setOwnerSearchable`, and a new value `emptyPermissions`.

#### 1.7.10.9. dph (dph-base, dph-par, dph-prim-interface, dph-prim-par, dph-prim-seq, dph-seq)

- The dph packages are no longer shipped with GHC.

#### 1.7.10.10. extensible-exceptions

- Version number 0.1.1.2 (was 0.1.1.1)

#### 1.7.10.11. filepath

- Version number 1.2.0.0 (was 1.1.0.4)

- The current directory is now `"."` rather than `""`.

#### 1.7.10.12. ghc-binary

- This is an internal package, and should not be used.

#### 1.7.10.13. ghc-prim

- This is an internal package, and should not be used.

#### 1.7.10.14. haskell98

- Version number 1.1.0.0 (was 1.0.1.1)

- In the `Directory` module, the `Permissions` type and the `getPermissions` and `setPermissions` functions are now different to their equivalents in `base:System.Directory`.

#### 1.7.10.15. haskell2010

- This is a new boot package, version 1.0.0.0. It is not exposed by default.

#### 1.7.10.16. hpc

- Version number 0.5.0.6 (was 0.5.0.5)

#### 1.7.10.17. integer-gmp

- Version number 0.2.0.2 (was 0.2.0.1)

#### 1.7.10.18. old-locale

- No change (version 1.0.0.2)

#### 1.7.10.19. old-time

- Version number 1.0.0.6 (was 1.0.0.5)

#### 1.7.10.20. pretty

- Version number 1.0.1.2 (was 1.0.1.1)

#### 1.7.10.21. process

- Version number 1.0.1.4 (was 1.0.1.3)

#### 1.7.10.22. random

- Version number 1.0.0.3 (was 1.0.0.2)

#### 1.7.10.23. syb

- The syb package is no longer included with GHC.

#### 1.7.10.24. template-haskell

- Version number 2.5.0.0 (was 2.4.0.1)

- There is a new type synonym `DecsQ` in `Language.Haskell.TH.Lib`.

- There is a new `StringPrimL` constructor in `Language.Haskell.TH.Syntax.Lit`, and a new helper function `stringPrimL` for it in `Language.Haskell.TH.Lib`.

- There is a new function `quoteFile` in `Language.Haskell.TH.Quote`.

- The `Language.Haskell.TH.Quote.QuasiQuoter` type has two new fields: `quoteType` and `quoteDec`.

- There is a new `ClassInstance` type in `Language.Haskell.TH.Syntax`. The `Language.Haskell.TH.Syntax.Info.ClassI` constructor now includes a value of this type, which allows instance information to be queried via the new `isClassInstance` and `classInstances` functions. There is also a new method `qClassInstances` in the `Quasi` class.

#### 1.7.10.25. time

- Version number 1.2.0.3 (was 1.1.4)

- The types provided by the time package now include `Data` instances.

#### 1.7.10.26. unix

- Version number 2.4.1.0 (was 2.4.0.2)

- There are three new helper function in `System.Posix.Error`: `throwErrnoPathIfRetry`, `throwErrnoPathIfNullRetry` and `throwErrnoPathIfMinus1Retry`.

- There are three new functions in `System.Posix.User`: `setEffectiveUserID`, `setEffectiveGroupID` and `setGroups`.

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