My first email seems to have gotten lost, if it meanders it's way here, then sorry for the repeat. Anyways, generating a set of pattern matching functions in an instance declaration (maybe in general, though I haven't tested it) causes a "conflicting definitions error". Rewriting as a case expression is one work-around. E.g. instance (NFData a) => NFData (Tree a) where rnf (Leaf a) = rnf a rnf (Branch a b) = rnf a `seq` rnf b doesn't work, but rewriting as instance (NFData a) => NFData (Tree a) where rnf x = case x of (Leaf a) -> rnf a (Branch a b) -> rnf a `seq` rnf b does. I suspect that it may have to do with the generated code being considered at a lower level (i.e. the transformation of the above into the below is already considered done). It may just be I'm creating the functions incorrectly, so if you can't get the error to happen I can provide the code I'm using. Separately: I've written a variety of fold algebras over data declarations. I'm not sure how useful they'll be, but if you're interested email me, and I'll email the source. I haven't tested them, but it's pretty mechanical code so I don't suspect any major problems and any should be relatively straightforward to fix. See `Dealing with Large Bananas` for the concept (and for documentation, as it has no documentation yet). _________________________________________________________________ STOP MORE SPAM with the new MSN 8 and get 2 months FREE* http://join.msn.com/?page=features/junkmail