GHC 2.06 is a minor upgrade of GHC 2.05, and is released as source only.  It represents work done through August '97.

Here's a list of the changes made since GHC 2.05:

\begin{itemize}

\item Fix to reader to allow let expressions in pattern guards.

\item Tidied up @nofib/parallel@

\item Changed derived @Show@ (and @Read@) code for constructors
with labelled fields to bring them into line with the Report.

\item Fixed @ghc-0.29 -O@ booting problem (codeGen/ClosureInfo not closed.)

\item Improved error messages for illegal derivings of @Ix@, @Enum@
and @Bounded@.

\item Fixed bug in deriving @Ix@ code. (need to actively slurp in
return and zero)

\item New module: @PackBase@ - minimum pack/unpack code.

\item Moved @PackedString@ to ghc system library

\item Added export of @unionBy@ and @intersectBy@ to @List@ (plus
commented out unused functions).

\item Uniform size to @ForeignObj@ closures (indep of GC scheme).

\item Added @ForeignObj@ support to NCG

\item Added @index*OffForeignObj#@ primops (for completeness, mostly)

\item Removed: @Util.mapAccumL@ and @Util.mapAccumR@ (now via List)

\item Removed: @forall@ and @exists@ from @Util@ (now @any@ and @all@ from @Prelude@). 

\item fixed: handling of source input from stdin in the driver.

\item x86 NCG should now compile under 2.0x

\item PECULIAR: compiling -prof "fixes" simplifier performance on deep
  list comprehensions.

\item Added -O for ghc/lib/cbits

\item Updated @lndir@ (sync wrt. X11R6.3)

\item Removed @glafp-utils/msub@

\item Fixed misleading error message for guards (used to
mention list comprehensions)

\item Fixed incorrect handling of default methods (used to
complain about differing contexts)

\item Fixed missing @tidyPrimOp@ in @simplCore/SimplCore@
	(Sven Panne bug report.)

\item Fixed desugaring of record construction for overloaded
constructors. (Dave Barton bug report.)

\item Fixed rank-2 polymorphism bug (Ralf Hinze bug report.)

\item Fixed interface-file parser error on @GHC.->@

\item Added @-no-recomp@ flag

\item Changed grouping syntax for simplifier opts, instead of
  '(' and ')', use '[' and ']'. The change is made to make
  it more Win32 (and cygwin32) friendly.

\item Removed the use of @COMPILING_GHC@ in @ghc/compiler/@

\item Use @COMPILING_NCG@ instead of @COMPILING_GHC@ in @ghc/includes/@
  header files to control visibility of info needed when
  compiling the native code generator.

\item Tidied up handling of IO error messages in @IOBase@

\item Fixed @PackBase.unpackCString@ and @PackedString.unpackCString@
to handle @NULL@ pointer arg gracefully.

\item fix: archives in @INSTALL_LIBS@ are now ranlib'ed when installing.

\item fix: for @-monly-x-regs@, the mangler now generates necessary code
  for loading up unstolen registers before GC, and save their updated
  contents (via BaseReg) on GC return before `handing back'
  the registers. This change fixed the @SIGSEGV@ problem reported by
 David Barton on an x86 platform (linux) with 2.05.

\item changed @SMstats.elapsedtime@ to return non-negative floats. (=>
  no more @-Rghc-timing@ warnings about not finding @InitTime@ etc.)

\item Change @mkWrapper@ in @WwLib.lhs@ to call
  @splitForAllTyExpandingDicts@ instead of @splitForALlTy@ to fix
 @absApply@ crash. (Jon Mountjoy bug report.)

\item GHC's interface file parser now uses the latest version of
Happy.

\item Happy is now included in the source distribution.
\end{itemize}