Leaving Data.Generics.Basics in base while moving Data.Generics.Instances to syb raises the interesting issue of dealing with the accidental re-exports of Data.Generics.Instances from various places. Here is that list again (*): $ find . -name '*hs' | grep -v _darcs | xargs grep -l 'Data.Generics' | grep -v Generics ./array/Data/Array.hs ./base/Data/Typeable.hs ./bytestring/Data/ByteString/Internal.hs ./bytestring/Data/ByteString/Lazy/Internal.hs ./bytestring/Data/ByteString/Unsafe.hs ./containers/Data/IntMap.hs ./containers/Data/IntSet.hs ./containers/Data/Map.hs ./containers/Data/Sequence.hs ./containers/Data/Set.hs ./containers/Data/Tree.hs ./haskell-src/Language/Haskell/Syntax.hs ./network/Network/URI.hs ./packedstring/Data/PackedString.hs ./template-haskell/Language/Haskell/TH/Quote.hs ./template-haskell/Language/Haskell/TH/Syntax.hs And here is a brief scan of what each of these is doing. References to 'standard' vs 'dubious' Data instances are wrt the suggested split in [1], with some possible refinements: - array: the Data instance for Array could be moved into array, avoiding the need for instance imports and syb dependency? - bytestring: uses deriving, which for Internal.hs depends on Data instances for Int [standard] and (ForeignPtr Word8) [dubious]; would need to depend on syb; and import both standard and dubious instances :-( perhaps Data instances for type constructors with phantom types should be re-classified into Standard, given that there are no data objects to be traversed? - containers: IntMap.hs, IntSet.hs, Map.hs, Sequencs.hs, Set.hs, Tree.hs define their own Data instances, or derive them in such a way that they do not need to import any instances :-) - haskell-src: uses deriving, will need to depend on syb; depends almost exclusively on standard instances (the only exception I can see in a quick scan is Rational); perhaps this is an argument in favour of moving the Data instance for 'Ratio a' from Dubious to Standard: the parameter type is never meant to be traversed, and tainting every client of 'Ratio a' with the really bad instances is not a good idea. Opinions? - network: uses deriving, will need to depend on syb; depends only on standard instances - packedstring: defines its own instances, no need to import any - template-haskell: uses deriving, roughly the same situation as for haskell-src? Claus [1] see the last page of http://www.haskell.org/pipermail/libraries/2008-July/010313.html [2] http://www.cs.kent.ac.uk/~cr3/toolbox/haskell/#syb-utils