Release notes for version 2.09 -- 11/97

• fixed type-synonym-arity bug in the typechecker.
• fixed overloaded-constructor-argument bug in the typechecker.
• fix off-by-one error in `PackedString:filterPS'.
• fixed `getCurrentDirectory'.
• fixed space-leak bug to do with polymorphic recursion and overloading.
• fixed lit-deatify that was core dumping on Linux.
• some fixes to the native code generator for i386.
• unboxed the state in ST and IO, and specialised IO (it is no longer built on top of ST).
• reversed the sense of `-fwarn-{overlapped,incomplete}-patterns'. The driver now has to have the flag to provide the warning.
• added `-fwarn-missing-methods'.
• added the `-Wnot', `-W', and `-Wall' options. Set up a default set of warnings, namely `-fwarn-{overlapped,incomplete}-patterns'.
• Added `-fwarn-duplicate-exports' warning to check for duplicates in export lists. Included in default warning set.
• Renamed `SampleVar.{write,read}Sample' to `SampleVar.{write,read}SampleVar'.
• 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.
• removed the `PrimIO' type. For a limited time only, `PrimIO' will be available from `GlaExts' as a synonym for `IO'.
• changed the type of `_ccall_'s to return `(IO a)'.
• renamed `mainPrimIO' to `mainIO', as it now has type `IO ()'.
• fixed the semantics of the `-i' flag to `mkdependHS' to be the same as GHC.
• fix panic when a type constructor is used as a class.
• don't arbitrarily truncate cost centre names in profiling information.

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).

• `Addr' moved out of `Foreign' and into its own module.
• `MutVar' module disappeared, `IOExts' now exports `IORefs' and associated operations.
• 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.
• A new module `IOExts' provides extensions to the `IO' monad, including `unsafePerformIO', `unsafeInterleaveIO', `IORef's (mutable variables), and `IOArray's (mutable arrays).
• 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).
• 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.
• 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.
• Added `Bits', `Int', `Word' (and a few new primops over words).
• 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.
• Several changes to the libraries in `lib/ghc' - see the User Guide for details.