Release~0.23 is the fifth public release of Glasgow Haskell.
It incorporates our new work for the second half of 1994.

The announcement for this release is distributed as \tr{ANNOUNCE-0.23}
in the top-level directory.

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\subsection[0-23-ports]{What machines GHC~0.23 runs on}
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NOTE: the porting situation is essentially unchanged between 0.22 and
0.23, except for adding the native-code generator for DEC Alphas.

We use Sun4s running SunOS~4.1.3 and DEC~Alphas running OSF/1~V2.0, so
those are the ``fully-supported'' platforms, unsurprisingly.  Both
have native-code generators, for quicker compilations.

The GHC hierarchy of Porting Goodness: (a)~Best is a native-code
generator; (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 0.23:
\begin{description}
%-------------------------------------------------------------------
\item[Sun4 running SunOS~4.1.3 (\tr{sparc-sun-sunos4}):]
Fully supported, including native-code generator.

%-------------------------------------------------------------------
\item[Sun4 running Solaris 2.x (\tr{sparc-sun-solaris2}):]
Fully supported, including native-code generator.
(NB: not tested before release.)

%-------------------------------------------------------------------
\item[DEC Alpha running OSF/1 V2.0 (\tr{alpha-dec-osf1}):]
Fully supported, including native-code generator.

%-------------------------------------------------------------------
\item[Sun3 running SunOS~4.1.3 (\tr{m68k-sun-sunos4}):]
GHC~0.23 works registerised.  No native-code generator.

%-------------------------------------------------------------------
\item[HP-PA box running HP/UX 9.x:]
An unregisterised port of 0.21 (last ``internal'' release before 0.23)
seems to work, except that floating-point is definitely busted.
0.23~should be the same.

%-------------------------------------------------------------------
\item[Silicon Graphics box running IRIX 5.x:]
An unregisterised port of 0.21
seemed to work.  0.23~should be the same.

%-------------------------------------------------------------------
\item[DECstation (MIPS-based):]
An unregisterised port back around the time of 0.17 seemed to work;
0.23~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.  Had a report that things were basically OK at 0.22.

%-------------------------------------------------------------------
\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[0-23-config]{New configuration things in 0.23}
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Essentially, upgraded to Autoconf~2.  Probably the easiest way to see
what all the options are now is to type \tr{./configure --help} and
look at the stuff near the end.

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\subsection[0-23-user-visible]{User-visible changes in 0.23, 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''.)  Some day, we will stop doing this to you :-)

Monadic I/O has taken yet another shake-up; that is outlined in the
next section.

To use the 1.3-DRAFT I/O features, you use a \tr{-fhaskell-1.3} flag.
This also nets you, from your Prelude, the \tr{Maybe} and \tr{Either}
types, and the functions \tr{thenMaybe}, \tr{curry}, and \tr{uncurry}.

The driver supports a heap-and-stack-sizes scaling flag.  For example,
\tr{-Rscale-sizes2} would cause the driver to use twice as much
heap/stack space as it would otherwise.  This is a convenient way to
move between machines with differing memory setups (e.g., 32-bit vs
64-bit) without changing millions of -H flags in a Makefile.  Note:
something like \tr{-Rscale-sizes1.5} is OK, too.

``Lit-lit'' literals are now overloaded.  They can be any
\tr{_CCallable} type, not just \tr{_Addrs}.  The price of this extra
convenience is that you sometimes have to insert a type signature.

The shift-right primitive-operation, \tr{shiftR#}, has been renamed
and clarified to \tr{shiftRA#} (arithmetic).  A new prim-op
\tr{shiftRL#} (logical) has been added.

Comparable shift primitive-ops on \tr{Int#s} (rather than \tr{Word#s})
have been added: \tr{iShiftL#}, \tr{iShiftRA#}, and \tr{iShiftRL#}.
Long live high-level languages!

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\subsection[0-23-io]{New in I/O, esp. ``monadic,'' esp. ``1.3''}
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GHC~0.23 is still a Haskell~1.2 compiler.  Do nothing weird, and it
should work exactly as before.

If you give GHC a \tr{-fhaskell-1.3} flag (both compile and link time,
please!), it will use a VERY EARLY, LARGELY UNTESTED implementation of
the DRAFT 1.3 I/O PROPOSAL.

The \tr{PreludeGlaIO} interface, which was based on a long-ago 1.3 I/O
proposal, is DEAD.  It was in a pretty bad state, anyway.
Putting \tr{PreludeGlaIO} code through as 1.3 code, I got pretty
far with just these few impedance-matching definitions:
\begin{verbatim}
> type Void = ()
> returnIO = return
> thenIO = (>>=)
> mapIO	 :: (a -> IO b) -> [a] -> IO [b]
> mapIO f =  accumulate {-was:listIO-} . map f
\end{verbatim}

We supply the DRAFT 1.3 I/O PROPOSAL in \tr{ghc/docs/io-1.3/}.
It is in HTML format.

We still give access to our underlying \tr{PrimIO} monad, via the
\tr{PreludePrimIO} interface.  This is the level at which \tr{_ccall_s}
operate.  It should still be quite solid, and counts as a good fall-back
position when the 1.3-DRAFT stuff dies on you.  See the User's Guide.

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\subsection[0-23-support]{New in support tools (e.g., profiling)}
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The reports from profiling should be a bit tidier.  The ``automagic''
cost-centres for, e.g., ``all the CAFs in module X'', will now be
reported against \tr{CAFs_in_... X}.  Which seems fair enough.

GHCI---an INTERPRETER for Glasgow Haskell!  The brainchild and work of
Alastair Reid, before he defected to the Enemy at Yale.  Accepts full
Glasgow Haskell, including many extensions.  Can mix interpreted and
compiled code, the Prelude being a notably case of the latter.
MASSIVE HACK VALUE!  The problem is it doesn't quite compile under
0.23 (I ran out of time), and some of its dodgy bits (used to mix
interpreted and compiled code) need upgrading to work with the new
info tables.  It lives in \tr{ghc/compiler} and below, notably the
\tr{interpreter} subdirectory.  Don't be shy now---roll up your
sleeves and strut your hacking stuff!

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\subsection[0-23-new-in-compiler]{New in the compiler proper}
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The compiler is quite a bit faster at compiling, {\em without}
\tr{-O}.  We are in the HBC league now.  I don't remember all the
HACKs that we threw in to make this happen :-)

New-format ``info tables'' (work by Bryan O'Sullivan and friends).
Essentially, static info used by the garbage-collector has been moved
one indirection further away, into a ``rep table,'' of which there are
a fixed number.  So the same GC info isn't replicated over and over
again.  This is our main space-savings gain in 0.23.

A native-code generator for the DEC Alpha.  Jim Mattson did it in one
weekend.  What a great system!

Rather than have a separate Yacc-parser process that spews a long
``prefix form'' string into the compiler, the compiler now just does a
\tr{_ccall_ yyparse} and then walks the resulting parse tree directly.
(Not quite {\em that} simple, but... still pretty cool.)

A {\em selective} lambda-lifter.  (Simon is very excited about its
selectiveness.)  That means it only does lambda-lifting if there is a
benefit in doing so.  It's done on the STG syntax (quite late in the
compilation).

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\subsection[0-23-new-in-libraries]{In the prelude and runtime support}
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PackedStrings (now called \tr{_PackedString}s) are now a built-in
type, just like \tr{Int}s, say.  Their interface is described with the
Glasgow extensions in the User's Guide.  There is also a
``extensions-free'' interface (no underscores on the front of names)
which you can get at as a system library (\tr{-syslib ghc}).

The pretty-printing code that we use in GHC is now available in the
GHC system library (\tr{-syslib ghc} and \tr{import Pretty}).  We
would claim it is more ``industrial strength'' than the one in the HBC
system library...

Because of name-grabbing by the DRAFT-1.3-I/O, two functions in the
HBC library's \tr{Parse} module have been renamed: \tr{(>>)} is now
\tr{act}, and \tr{fail} is now \tr{failP}.  (We will change these
again if Lennart does something differently.)

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\subsection[0-23-new-elsewhere]{Other new stuff}
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We've added a new utility, \tr{pphs}, for pretty-printing Haskell code
in LaTeX documents.  It was written by Andrew Preece, a student at
Glasgow.  The code is in \tr{ghc/CONTRIB/pphs}.

Over in literate-land, we've hidden a copy of a slightly-tweaked
\tr{texi2html} script (in \tr{literate/texi2html/texi2html}).  This is
probably the most painless way to turn ``literate'' things into
Webbable HTML documents.  (Use our literate stuff to make Texinfo
files, then convert with \tr{texi2html}.)  NB: not really tested.