GHC 2.03 is a minor upgrade of GHC 2.02.  It differs in the following
ways:

\begin{itemize}
\item
    A slew of small bugs are fixed.  You can find the complete list
    at:

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

    One bug remains un-fixes, namely the crash when there's an empty 
    comment at the end of file.  It's wierd!

\item
    Last-minute language changes have been implemented (minor changes
    to the libraries, and to module export/hiding scope rules)

\item
    It is only available as a source distribution.  If you want to
    use it you'll have to build it from source.  Nowadays this is
    a well-documented process (see the build and installation guide, but
    note that this release is still not self-booting, you still need
    to have The Good Old Compiler (0.29) at your disposal).
\end{itemize}

None of the bugs in GHC 2.02 are show-stoppers, so you'll only want
to upgrade if you are a build-from-source junkie and the bugs are 
irritating you.

Apart from bug-fixes, which are itemized elsewhere, 
the exact language and standard-library changes are as follows:
\begin{itemize}
\item
A hiding clause hides the unqualified name, but not the qualified name.
\item 
There's a new @Numeric@ library, containing mostly mildly marginal
code for showing and reading numbers.  Parts of its exports used to be
exported by @Prelude@, but now you'll have to import them explicitly.
It also defines some functions that weren't provided before; have a
look in the Haskell library report for details of complete interface.
\item
The following extra functions are exported from @IO@: 
@try@, @bracket@, @bracket_@, @hGetLine@, @hWaitForInput@.
\end{itemize}

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

\begin{itemize}
\item The function @fromRational__@, exported from @PrelNum@, is now called @fromRat@.
(And it's exported by @Numeric@.)
\item
Documentation for the Glasgow specific interfaces plus the system
libraries have been re-instated. Posix library documentation included also.
\item
@maybe@ is now exported from Prelude, as it should have been in 2.02.
\item
Equality on @IO.Handle@ is now defined as specified by the library
report.
\item
@Ix.rangeSize@ returns \tr{0} on an empty range;previously it failed.
\item
The new interface @GlaExts@ which is meant to be the gateway to the
various Glasgow extensions has now been documented.
\item
@GlaExts@ now exports the representation of @Char@.
\item
The mutable variable interface, @MutVar@, has also been documented,
together with @ByteArray@, @MutableArray@ and @Foreign@.
\item
Added documentation on how to compile mutually recursive modules with
2.03.
\end{itemize}