[Haskell-cafe] portable arrow instances

[Ross Paterson]

On Tue, Nov 18, 2008 at 03:01:00PM +0100, Wolfgang Jeltsch wrote:
> how do I make a library work with both GHC 6.8 and GHC 6.10?  According to 
> <http://www.haskell.org/haskellwiki/Upgrading_packages#Arrow_instances>, I 
> should change all my Arrow instances but then they don't work with GHC 6.8 
> anymore, do they?  Or is the solution to force GHC 6.8 users to use 
> base-4.0.0.0?

GHC 6.8 users can't use base-4.  I think it's either two versions or cpp.