GHC 2.04 is a minor upgrade of GHC 2.02 (and the bugfix release,
2.03), representing work done through May '97. This new release
adds the following:

\begin{itemize}
\item
Data constructors can now have polymorphic fields, and ordinary
functions can have polymorphic arguments.  Details on

\begin{verbatim}
	http://www.cse.ogi.edu/~simonpj/quantification.html
\end{verbatim}

Existential types coming, but not done yet.

\item Pattern guards implemented, see
	
\begin{verbatim}
http://www.cse.ogi.edu/~simonpj/guards.html
\end{verbatim}

\item Compiler can now compile itself.

\item \tr{INLINE} pragmas honoured (caveat: not yet
working on instance-decl methods) 

\item Simplifier improvements and better inlining gives
better code; not sure how *much* better.

\item \tr{-dshow-rn-stats} print out amusing statistics about what
the renamer does.

\item
When compiling without -O, the renamer (the pass responsible for
slurping in interface file and making sure everything is in scope
etc.) is now more careful about what it will bring in (especially
data constructors and instance declarations). The upshot of this
change is that a lot of the (unnecessary) work this pass did in
2.02/2.03 is now avoided.

\tr{-fno-prune-tydecls} and \tr{-fno-prune-instdecls} switch off these
renamer optimisations. You can try the effect with the renamer
statistics. War stories welcome.

\item
    The Heroic Efforts of \tr{Andr\'e Santos <alms@di.ufpe.br>} have
    been included, AIX/RS6000 is now a supported \tr{ghc}
    platform! Bug reports concerning this port to (as always)
    \tr{glasgow-haskell-bugs@dcs.gla.ac.uk}.

\item
    A lot of the bugs that were present in versions 2.02/2.03
    have been fixed (thanks to everyone that reported bugs!).
    A list of the reported problems with 2.02/2.03 can be found at

\begin{verbatim}
    http://www.dcs.gla.ac.uk/fp/software/ghc/ghc-bugs.html
\end{verbatim}

    No doubt entries for 2.04 will be added here as well :-)

\item
    This release is available in source format only. To build it you'll
    need to have either a copy of GHC~0.29 or GHC~2.02/3 installed.
    For people either doing porting work or work on a (supported) 
    platform for which there is no GHC binary bundles available, the
    necessary intermediate files are also available (.hc and .hi files).

    Consult the installation guide for more information on how
    to build or bootstrap. The guide is included in the distribution
    (in the fptools/docs directory), and an on-line version of the
    document can be found at

\begin{verbatim}
    http://www.dcs.gla.ac.uk/fp/software/ghc/ghc-doc/install-guide.html
\end{verbatim}
\end{itemize}

In addition to the above, we've made the following minor changes to
the GHC libraries/our implementation of the Haskell standard prelude:

\begin{itemize}
\item
\tr{isPrefixOf} and \tr{isSuffixOf} has been added to \tr{List}.
\item
The empty type \tr{Void} is now exported from the prelude.
\item
\tr{GlaExts} exports the \tr{Lift} data type:

\begin{verbatim}
data Lift a = Lift a
\end{verbatim}

you might need it someday...

\item
The \tr{Foreign} interface now also exports the representations
for \tr{Word} and \tr{Addr}.

\item The low-level file handle interface in the \tr{POSIX} system
library has been reworked a bit, most notably is the renaming of
\tr{Channel} to \tr{Fd} and the introduction of operations for converting
to and from \tr{Handle} and \tr{Fd} values. The changes are:

\begin{verbatim}
--Renamed functions (old name in square brackets)
openFd :: FilePath       
       -> OpenMode 
       -> Maybe FileMode 
       -> OpenFileFlags 
       -> IO Fd
 -- [openChannel]
fdSeek  :: Fd -> SeekMode -> FileOffset -> IO FileOffset 
 --[seekChannel]
fdRead  :: Fd -> ByteCount -> IO (String, ByteCount)     
 --[readChannel]
fdWrite :: Fd -> String -> IO ByteCount                  
 --[writeChannel]
fdClose :: Fd -> IO ()          
 --[closeChannel]
setFdOption :: Fd -> FdOption -> Bool -> IO ()
 --[setChannelOption]
queryFdOption :: Fd -> FdOption -> IO Bool
 --[queryChannelOption]
dup :: Fd -> IO Fd
 --[dupChannel]
dupTo :: Fd -> Fd -> IO ()
 --[dupChannelTo]

data FdOption = AppendOnWrite | CloseOnExec | NonBlockingRead
 --[ChannelOption]
getFdStatus :: Fd -> IO FileStatus
 --[getChannelStatus]

-- New data structure collecting together misc flags passed to openFd
data OpenFileFlags =
 OpenFileFlags {
    append    :: Bool,
    exclusive :: Bool,
    noctty    :: Bool,
    nonBlock  :: Bool,
    trunc     :: Bool
 }

--New ops for converting between Fd and Handle:
fdToHandle :: Fd -> IO Handle
handleToFd :: Handle -> IO Fd
intToFd    :: Int -> Fd -- use with care.
\end{verbatim}

\end{itemize}