Release~2.01 is the first release of Glasgow Haskell for Haskell~1.3.
It represents a major step forward in GHC development since GHC~0.26
(July 1995).  Note that we are also releasing GHC~0.29, the current
state-of-play with the Haskell~1.2 compiler---at the same time as
2.01.

The announcement for this release is distributed as @ANNOUNCE-2.01@
in the top-level directory.  It contains very important caveats about
2.01, which we do not repeat here!

Information about ``what's ported to which machine'' is in the
Installation Guide.  Since 0.26, we've improved our support for iX86
(Intel) boxes, notably those running Linux.

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<sect1>New configuration things in 2.01
<label id="2-01-config">
<p>
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<sect1>User-visible changes in 2.01, including incompatibilities
<label id="2-01-user-visible">
<p>
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GHC~2.01 is a compiler for Haskell~1.3 and, as such, introduces many
user-visible changes.  The GHC user's guide has a section to help you
upgrade your programs to Haskell~1.3; all user-visible changes
are described there (and not repeated here).

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<sect1>New or changed GHC command-line options
<label id="2-01-options">
<p>
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A new flag, @-recomp@ invokes the new ``recompilation checker.''
We recommend that you use it whenever you use `make' to build your
Haskell programs.  Please see the User's Guide for details.

The flags @-fomit-derived-read@ and
@-fomit-reexported-instances@ have died; there is no longer any
need for them.

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<sect1>New in the compiler proper
<label id="2-01-new-in-compiler">
<p>
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Substantially rewritten.  Notable points:
<itemize>
<item>
The typechecker, besides doing all the new 1.3
features (constructor classes, records, etc.), has been made
ready to do linear types (e.g., there are now ``usage
variables'' as well as ``type variables'').

<item>
The Core language now has one constructor for lambdas
(@Lam@; rather than two, @CoLam@ and @CoTyLam@);
also, one constructor for applications (@App@, rather
than two, @CoApp@ and @CoTyApp@).

Consequently, new more-general datatypes for binders and
arguments now exist (@CoreBinder@ and @CoreArg@,
respectively).

Again, the Core language is now ``linear types''-ready
(though the work hasn't been done yet).

A new Core constructor, @Coerce@, exists to support the
1.3 @newtype@ construct.

<item>
The ``renamer''---the part of the compiler that implements
the Haskell module system---has been completely rewritten.

In part, this is because the 1.3 module system is radically
changed from 1.2, even if the user is unlikely to notice.

We've implemented the new system with a ``go to the
horse's mouth'' scheme; that is, to discover the facts about
an entity @Foo.bar@, we <em>always</em> go to the interface
for module @Foo@; hence, we can never get duff information
about @bar@ from some intermediary.

Interface files are no longer mandated by the language, so
they are completely different in 2.01 compared to 0.2x.  They
will very likely change again.  All processing of interface
files is done in Haskell now (the most likely reason why GHC
has slowed down :-().

<item>
Much less special pleading for the Prelude.  If you wanted
to write your own Prelude and drop it in, you would have
a fighting chance now.

<item>
No more `make' dependency loops!  (Hooray!) The whole compiler
will build in one `make' run, no fuss or bother.
</itemize>

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<sect1>In the ``required'' libraries (incl. Prelude)
<label id="2-01-new-in-libraries">
<p>
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We support standard 1.3 monadic I/O, to the best of our knowledge.

The proposal for @LibPosix@ didn't make it into Haskell 1.3 I/O.
So it's now a system library, @-syslib posix@.  (And, of course,
the @Lib@ prefix is gone.)

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<sect1>New in ``Glasgow extensions'' library things
<label id="2-01-new-in-glaexts">
<p>
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The @PreludeGlaMisc@ and @PreludePrimIO@ interfaces have died.
Use @PreludeGlaST@ instead.

We don't really know what our interfaces-to-nonstandard-things will
eventually look like...

MallocPtrs now called ForeignObjs

The @_PackedString@ gunk (with leading underscores) is gone.  Just
@import PackedString@ and use ``normal'' names.

All of the following are <em>gone</em>:
<tscreen><verb>
data _FILE  -- corresponds to a "FILE *" in C

fclose  :: _FILE -> PrimIO Int
fdopen  :: Int -> String -> PrimIO _FILE
fflush  :: _FILE -> PrimIO Int
fopen   :: String -> String -> PrimIO _FILE
fread   :: Int -> Int -> _FILE -> PrimIO (Int, _ByteArray Int)
freopen :: String -> String -> _FILE -> PrimIO _FILE
fwrite  :: _ByteArray Int -> Int -> Int -> _FILE -> PrimIO Int

appendChanPrimIO :: String -> String -> PrimIO ()
appendFilePrimIO :: String -> String -> PrimIO ()
getArgsPrimIO	 :: PrimIO [String]
readChanPrimIO	 :: String -> PrimIO String
</verb></tscreen>

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<sect1>In the ``system'' libraries
<label id="2-01-new-in-syslibs">
<p>
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The ``system'' libraries are no longer part of GHC (they lived in
@ghc/lib/@); they have been lifted out into a subsystem in their
own right (they live in @hslibs@).

Of course, a GHC distribution will ``happen'' to have these libraries
included; however, we hope the libraries will evolve into a large,
flourishing, independently-maintained, and independently-distributed
body of code---preferably compiler-independent, too!

Renamings in the GHC system library (@hslibs/ghc/@): The function
@BitSet.singletonBS@ is now called @unitBS@.  Similarly,
@FiniteMap.singletonFM@ is now @unitFM@.  @Set.singletonSet@
lingers briefly; @unitSet@ is also available now.

We are <em>not</em> up-to-date with the HBC-for-1.3's HBC library (the source
hasn't been released yet).

The @Either@, @Maybe@, and @Option@ modules in the HBC
library (@hslibs/hbc/@) have been deleted---they are too close to
what Haskell~1.3 provides anyway (hence, confusing).

The POSIX support code is in @hslibs/posix@.

We have added a ``contrib'' system library (@hslibs/contrib/@);
made up of code that was contributed to the ``Haskell library'',
mostly by Stephen Bevan.  Quite of bit of code for numerical methods
in there...

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<sect1>In the runtime system
<label id="2-01-new-in-rts">
<p>
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We have made a point <em>not</em> to beat on the runtime system very much.
Some bugs have been fixed since 0.26, of course.

The GranSim (parallel-machine simulator) stuff is substantially improved
(but you're better off using the 0.29 version of it).

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%<sect1>Other new stuff
<label id="2-01-new-elsewhere">
<p>
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