Release~0.22 is the fourth public release of Glasgow Haskell.
It incorporates our new work for the first half of 1994.

The announcement for this release is distributed as \tr{ANNOUNCE-0.22}
in the top-level directory.

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\subsection[0-22-ports]{What machines GHC~0.22 runs on}
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We use Sun4s running SunOS~4.1.3 and DEC~Alphas running OSF/1~V2.0, so
those are the ``fully-supported'' platforms, unsurprisingly.  For
Sun4s, we have a native-code generator, which makes for somewhat
quicker compilations.  (We actually produce better code by compiling
intermediate C with GCC.)

The GHC hierarchy of Porting Goodness: (a)~Best is a native-code
generator [only for Sun4s, now]; (b)~next best is a ``registerised''
port; (c)~the bare minimum is an ``unregisterised'' port.
``Unregisterised'' Haskell programs are much bigger and slower,
but the port is much easier to get going.

Here's everything that's known about GHC ports, as of 0.22:
\begin{description}
%-------------------------------------------------------------------
\item[Sun4 running SunOS~4.1.3:]
Fully supported, including native-code generator.

%-------------------------------------------------------------------
\item[DEC Alpha running OSF/1 V2.0:]
Fully supported, but no native-code generator (none planned).

%-------------------------------------------------------------------
\item[Sun3 running SunOS~4.1.3:]
GHC~0.22 should work, registerised.  (0.21 did work.)

%-------------------------------------------------------------------
\item[Sun4 running Solaris 2.x:]
We expect to finish a ``registerised'' port ourselves, in the
foreseeable future.  Feel free to ask about it, if interested.  Not
sure about native-code...

%-------------------------------------------------------------------
\item[HP-PA box running HP/UX 9.x:]
An unregisterised port of 0.21 (last ``internal'' release before 0.22)
seems to work, except that floating-point is definitely busted.
0.22~should be the same.

%-------------------------------------------------------------------
\item[Silicon Graphics box running IRIX 5.x:]
An unregisterised port of 0.21
seemed to work.  0.22~should be the same.

%-------------------------------------------------------------------
\item[DECstation (MIPS-based):]
An unregisterised port back around the time of 0.17 seemed to work;
0.22~should be the same, modulo a little bit-rot.

%-------------------------------------------------------------------
\item[x86 PCs running Linux/NetBSD/FreeBSD:]
This really needs a native-code generator to be viable.  No
recent progress.

%-------------------------------------------------------------------
\item[GRIP multiprocessor:]
GRIP is a 68020-based multiprocessor for running parallel Haskell
programs; too bad we have the only machine!  We run GHC~0.16 on it,
with no plans to upgrade.

We are working on other parallel stuff.  Stay tuned.

%-------------------------------------------------------------------
\item[NeXT box running whatever NeXTs run:]
Carsten Schultz succeeded with a ``registerised'' port of GHC~0.19.
There's probably a little bit-rot since then, but otherwise it should
still be fine.

%-------------------------------------------------------------------
\item[Macintosh, using MPW:]
As mind-blowing at it may seem, David Wright in Tasmania has actually
gotten GHC to run on a Macintosh.  Ditto James Thomson here at Glasgow.
You may be able to get Thomson's from here.  (Not sure that it will
excite you to death, but...)
\end{description}

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\subsection[0-22-user-visible]{User-visible changes in 0.22, including incompatibilities}
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You'll need to recompile everything if you're switching from a
previous version of GHC.  (If you don't, you'll get ``consistency
errors''.)

Lazy pattern-matching (e.g., \tr{let (x,y) = ... in ...}) no longer
carries with it the threat of a space leak.  (It used to be that, as
long as {\em either} of \tr{x} or \tr{y} was ``live,'' the storage
manager would hang onto {\em both} chunks of graph.)  No longer.

We've done a complete overhaul of the state-transformer stuff which
underlies our array, I/O, and C-calling support.  The ``state
interface document,'' distributed in \tr{ghc/docs/state-interface.dvi}
defines what we have done.  You may wish to check our abstracts
(\tr{ghc/docs/abstracts/}) to find papers about this stuff.  If you've
written code that grovels around in GHC innards (e.g., uses
``primitive operations'' directly), it will probably need updating.

We do {\em not} support Haskell~1.3 monadic I/O (any draft version),
but we will once the dust settles.  We still support the
\tr{PreludeGlaIO} interface that we have had for some time.

You can now build GHC to support ``threaded'' execution.  (Configure
\tr{--with-threads=yes}, then use GHC with a \tr{-threads} option.)
Using the \tr{_seq_} and \tr{_par_} constructs,

GHC does a better job of not stealing from the user's name space (for
its own extensions, etc.).  For example, the ``set cost-centre''
keyword is now \tr{_scc_}, rather than \tr{scc} (though the latter
will continue to be accepted for a while).  With the
\tr{-fglasgow-exts} flag on, names may begin with an underscore
(\tr{_}).

We have friendly interaction between ``Haskell land'' and ``C land''
via (a)~{\em stable pointers} (pass Haskell pointers to C and have the
garbage-collector not forget about them); and (b)~{\em malloc
pointers} (return C pointers to Haskell and tell Haskell ``throw this
away when you're finished with it'').  See the User's Guide for more
info.

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\subsection[0-22-support]{New in support tools (e.g., profiling)}
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%************************************************************************

The profiling system of GHC has been improved in version~0.22 in the
following ways:
\begin{description}
\item[Now uses the ``hybrid scheme'':] (Rather than pure ``lexical
scoping'') What this means for you: ``CAF'' cost-centres will no
longer be blamed for gigantic chunks of the time in your program.

\item[Uses the generational garbage-collector:] (At least when doing
time profiling)  It used to use a two-space copying GC; it still does
when space profiling.  You should be able to profile larger programs.
\end{description}

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\subsection[0-22-new-in-compiler]{New in the compiler proper}
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The ``simplifier''---the program-transformation engine in the middle
of the compiler---has settled down (at least until Simon has another
Brain Wave).  We've made ``per-simplification'' flags, so that each
run of the simplifier can be controlled separately---this allows very
precise control.  (But makes it pretty hard to exercise any control
from the command-line.)  More in the docs.

Related to simplifier stuff was a revision of the ``unfoldery''
machinery.  We try very hard to find and exploit unfolding (or
inlining), including across module boundaries.

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\subsection[0-22-new-in-libraries]{In the prelude and runtime support}
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We've introduced a ``GHC system library,'' similar to the ``HBC system
library'' which we have supported for some time.  Just say
\tr{-syslib ghc} and the GHC library stuff is at your fingertips.
See the User's Guide for exactly what's on offer (not a lot right now,
but more will show up).

The @PackedString@ module that comes with the system is even beefier
than before; see the User's Guide.  (This module really should be
in the GHC library.)

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\subsection[0-22-new-elsewhere]{Other new stuff}
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We have two new mailing lists about Glasgow Haskell.
\begin{description}
\item[glasgow-haskell-users:]
This list is for GHC users to chat among themselves.  Subscribe by
sending mail to \tr{glasgow-haskell-users-request@dcs.glasgow.ac.uk}.
Messages for the list go to \tr{glasgow-haskell-users}.

\item[glasgow-haskell-bugs:]
This used to be an address for some lonely person who received bug
reports.  It is now a mailing list for the sort of people who discuss,
well, bug reports when they go to a party.

Subscribe via \tr{glasgow-haskell-bugs-request@dcs.glasgow.ac.uk};
send bug reports and rumination thereupon go to
\tr{glasgow-haskell-bugs}.
\end{description}