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1.4. Release notes for version 5.04

1.4.1. User-visible compiler changes

  • Full support for MacOS X, including fully optimized compilation, has been added. Only a native code generator and support for -split-objs is still missing. Everything else needs more testing, but should work.

  • ghc-pkg: new options --auto-ghci-libs, -u/--update-package, --force, and -i/--input-file, and suppport for expanding environment variables in package descriptions. See Section 4.10).

  • The latest version of the FFI spec is fully supported. The syntax of FFI declarations has changed accordingly. The old syntax is still accepted for the time being, but will elicit a warning from the compiler.

  • New option: -F specifies a user-defined preprocessing phase (see Section 4.12.4).

  • Major overhaul of the heap profiling subsystem, with new facilities for retainer profiling and biographical profiling (ala nhc98, albeit with a couple of omissions). The syntax of the runtime heap-profiling options has changed. See Section 5.4.

  • The type system now supports full rank-N types (previously only limited rank-2 types were supported). See Section 7.3.9.

  • Explicit kind annotations can now be given on any binding occurrence of a type variable. See Section 7.3.3.

  • The handling of type synonyms has been rationalised. See Section 7.3.10.

  • Fixes for several space leaks in the compiler itself (these fixes were also merged into 5.02.3).

  • It is now possible to derive arbitrary classes for newtypes. See Section 7.9.

  • Deadlock is now an exception, rather than a return status from the scheduler. See the module Control.Exception in the library documentation for more details.

  • The syntax and behaviour of RULE pragmas has changed slightly. See Section 7.7.

  • Interface files are now in a binary format to reduce compilation times. To view an interface file in plain text, use the --show-iface flag.

  • A restriction on the form of class declarations has been lifted. In Haskell 98, it is illegal for class method types to mention constraints on the class type variable. eg.

       class Seq s a where
          elem     :: Eq a => a -> s a -> Bool

    This restriction has now been lifted in GHC.

  • Main threads can now receive the BlockedOnDeadMVar exception in the same way as other threads.

  • The -fall-strict flag never really worked, and has been removed.

  • The syntax of .hi-boot files is now much clearer and Haskell-like. See Section 4.9.7.

  • There is a new flag -fffi which enables FFI support without turning on the rest of the GHC extensions.

  • The syntax for implicit parameter bindings has changed. Previously the keyword with was used to introduce implicit bindings, but now implicit bindings may be introduced using let (see Section 7.3.6). As a result of this, with is no longer a keyword when -fglasgow-exts is turned on.

    The option -fwith may be used to restore the old behaviour.

  • Infix type constructors are now allowed, and must begin with a colon (as with data constructors). See Section 7.3.2.

  • The do-notation syntax is now rebindable in the same way as other built-in syntax. See Section 7.5.4.

  • Support for using “frameworks” on Darwin/MacOS X has been added. See the -framework option in Section 4.12.7, and the framework_dirs field of a package spec in Section 4.10.4.

1.4.2. User-visible interpreter (GHCi) changes

  • New commands: :browse, :set args, :set prog, :show binadings, and :show modules (see Section 3.6).

  • There is a much more flexible mechanism for manipulating the scope for expressions typed at the prompt. For example, one can now have both the Prelude and the exports of several compiled modules in scope at the same time. See Section 3.4.1.

  • GHCi now supports foreign import "wrapper" FFI declarations.

1.4.3. User-visible library changes

  • GHC is in the process of moving to a new hierarchical set of libraries. At the moment, we have two sets of libraries, both described in accompanying documents:

    • The “new libraries” which are hierarchical and consist of the following packages: base, haskell98, haskell-src, and network. Broadly speaking, base contains the Prelude, standard libraries and most of the contents of the old lang package. By default, the base and haskell98 packages are enabled.

    • The hslibs, most of which are now deprecated. Where possible, new code should be written to use the new libraries instead.

      The following libraries in hslibs have not moved yet:

      • The packages win32, xlib, graphics, and posix.

      • The Edison libraries in the data package.

      • In the lang package, the modules TimeExts, DirectoryExts, SystemExts, and NumExts.

      • The HaXml libraries in the text package.

      • In the util package, the modules MD5, Select, Memo, Observe, and Readline.

      All other libraries from hslibs either have equivalents in the new libraries (see the hslibs docs for details), or were already deprecated and hence were not moved into the new hierarchy.

  • The Read class is now based on a parsing combinator library which is vastly more efficient than the previous one. See the modules Text.Read. Text.ParserCombinators.ReadP, and Text.ParserCombinators.ReadPrec in the library documentation.

    The code generated by the compiler for derived Read instances should be much shorter than before.

1.4.4. New experimental features

  • Linear implicit parameters. See Section 7.3.7.

  • The RTS has support for running in a multi-threaded environment and making non-blocking (from Haskell's point of view) calls to foreign C functions which would normally block. To enable this behaviour, configure with the --enable-threaded-rts option.

  • The compiler can now read in files containing Core syntax (such as those produced by the -fext-core option) and compile them. Input files with the .hcr file extension are assumed to contain Core syntax.

1.4.5. Internal changes

  • Happy 1.13 is now required to build GHC, because of the change in names of certain libraries.