Hi I just tried to compile a project of mine that builds fine using ghc 6.6.1 and got many errors like this: src/HyLo/Formula/NNF.hs:247:48: GADT pattern match in non-rigid context for `Opaque' Tell GHC HQ if you'd like this to unify the context In the pattern: Opaque f' In the expression: \ (Opaque f') -> Opaque (Box r f') In the definition of `box': box = \ (Opaque f') -> Opaque (Box r f') I don't know what a "non-rigid context" is, nor if "I like this to unify the context" or not, but I would certainly be happy if I could get this module to compile again! :) For the record, I was using ghc-6.8.0.20070917. Please let me know if you need further information.... Thanks Daniel PS: On a side note, I found this error message to be kind of funny. It seems to indicate no real error but some sort of error-message-driven poll!