Hi Lane,
I posted on the bug tracker earlier about doing this and now I am actually attempting it.
Fantastic!
I went to darcs.haskell.org/packages/ and decided arbitrarily to start with Data.Map, which I copied into the packages/ directory in yhc.
When I did a half attempt at this, I also started with Data.Map. However, that depends on Data.Typeable, which depends on Data.HashTable which depends on virtually every evil bit of Haskell. It was quite hard to find chunks of the base library which aren't intertwined.
As I understand it the preprocessor is turned off in yhc (thus the error).
By default, yes
As far as I can tell nothing else in packages/ uses preprocessor directives.
1) I should enable -cpp specifically for this file or globally for all of yhc, or just for packages/. (I'm not entirely sure how to get scons to do this but I need to take time and read the scons docs.)
I think this is the easiest one to do. I'd enable it for all packages/ in the scons script - compiling the other packages with -cpp is unlikely to be an issue. Andrew can probably advise about the scons side of things.
2) I should remove and work around the preprocessor directives. If I start making changes how does yhc keep in sync with any changes that are made to the base packages upstream?
You are very likely to need to make changes the the base repo, quite possibly substantial changes - often introducing new preprocessor directives etc to cope with Yhc. Integrating these patches back into the base library is definately a priority - once you have something that does something useful (but not necessarily complete by any means) we can contact the libraries@ list and set about getting the patches applied. Thanks Neil