<sect1>Release notes for version~2.09---11/97
<label id="release-2-09">
<p>

Changes made since 2.08:

<itemize>
<item> fixed type-synonym-arity bug in the typechecker.

<item> fixed overloaded-constructor-argument bug in the typechecker.

<item> fix off-by-one error in @PackedString:filterPS@.

<item> fixed @getCurrentDirectory@.

<item> fixed space-leak bug to do with polymorphic recursion and overloading.

<item> fixed lit-deatify that was core dumping on Linux.

<item> some fixes to the native code generator for i386.

<item> unboxed the state in ST and IO, and specialised IO (it is no longer built
  on top of ST).

<item> reversed the sense of @-fwarn-{overlapped,incomplete}-patterns@.
  The driver now has to have the flag to provide the warning.

<item> added @-fwarn-missing-methods@.

<item> added the @-Wnot@, @-W@, and @-Wall@ options.  Set up a default
  set of warnings, namely @-fwarn-{overlapped,incomplete}-patterns@.

<item> Added @-fwarn-duplicate-exports@ warning to check for duplicates in
  export lists. Included in default warning set.

<item> Renamed @SampleVar.{write,read}Sample@ to
  @SampleVar.{write,read}SampleVar@.

<item> new @mkdependHS@ options: @-W@ disables warnings of duplicate interface
  files found along the import path. @--include-prelude@ *will* generate
  dependencies on Prelude + any prelude/syslib .hi files used.

<item> removed the @PrimIO@ type.  For a limited time only, @PrimIO@
  will be available from @GlaExts@ as a synonym for @IO@.

<item> changed the type of @_ccall_@s to return @(IO a)@.

<item> renamed @mainPrimIO@ to @mainIO@, as it now has type @IO ()@.

<item> fixed the semantics of the @-i@ flag to @mkdependHS@ to be the
  same as GHC.

<item> fix panic when a type constructor is used as a class.

<item> don't arbitrarily truncate cost centre names in profiling information.
</itemize>

In 2.09, we've made extensive changes to the libraries that provide
access to various GHC extensions.  Many of these extensions are now
provided by Hugs, and as a result we are now using a common set of
extension libraries.

Briefly, the changes are as follows (for the definition of the new
libraries, see the section on GHC/Hugs libraries in the User Guide).

<itemize>
<item> @Addr@ moved out of @Foreign@ and into its own module.

<item> @MutVar@ module disappeared, @IOExts@ now exports @IORefs@ and
  associated operations.

<item> The @CCallable@ and @CReturnable@ classes now have their own
  module, @CCall@.  You only need to import this module to provide a
  new instance of one of these classes.

<item> A new module @IOExts@ provides extensions to the @IO@ monad,
  including @unsafePerformIO@, @unsafeInterleaveIO@, @IORef@s (mutable
  variables), and @IOArray@s (mutable arrays).

<item> Importing @ST@ is now the official way to get access to the @ST@
  monad.  This module also supports @STRef@s (mutable variables) and
  @STArray@s (mutable arrays).

<item> A new module @LazyST@ provides an identical interface to @ST@
  except that the underlying implementation of the monad is lazy.  Be
  careful about mixing these two in the same program.

<item> The new module @Bits@ provides a class of bit operations.  The
  modules @Int@ and @Word@ provide signed and unsiged integer types
  (respectively) of varying sizes, all of which support bit
  operations. 

<item> Added @Bits@, @Int@, @Word@ (and a few new primops over words).

<item> The @GlaExts@ module will provide Glasgow-only extensions.  For
  now, we've kept the old interface for compatibility, but beware that
  this is deprecated and the relevant extension libraries should be
  imported explicitly.

<item> Several changes to the libraries in @lib/ghc@ - see the User
  Guide for details.
</itemize>