Hi
I would think that nowadays the appropriate way to specify this is to put {-# LANGUAGE CPP #-} at the beginning of each file that needs it? see http://www.haskell.org/ghc/docs/latest/html/users_guide/pragmas.html#languag... "This allows language extensions to be enabled in a portable way. It is the intention that all Haskell compilers support the LANGUAGE pragma with the same syntax, although not all extensions are supported by all compilers, of course." ...
We have pragmas, so adding that shouldn't be too hard. If someone opens a bug for it, we won't forget. However for the base libraries, we want the minimal set of changes required to the code, to make it easier to get the changes integrated back in. GHC and Hugs both just preprocess all the base package with flags, we should do the same. Personally I think adding pragma's at the top of each file is a much better method, but for the base library if we want to do this we should probably ping libraries@ and see what people think - my guess is most will say no. Thanks Neil