base- not backwards compatible with base-

Ian Lynagh igloo at
Wed Nov 19 09:21:10 EST 2008

On Wed, Nov 19, 2008 at 03:06:04PM +0100, Stefan Holdermans wrote:
> Could anyone confirm the following claims?
> * base- (shipped with GHC 6.10.1) is supposed to be backwards  
> compatible with base- (shipped with GHC 6.8.3) ...


> * ... but it isn't! (For example, the Arrow class from Control.Arrow  
> is a subclass of Category from Control.Category in base-, but  
> not in base-

Yes. It wasn't possible to handle this change in a compatible way, I'm

> Do we know of any similar issues?

I think the Arrow/Category changes are the only issue. I think one of
the methods moved from one class to the other as well.

> What's the recommended workaround  
> when shipping code that is to support both GHC 6.8.* and GHC 6.10.*?)

CPP is the best solution I can think of.


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