Friends Just a heads-up. Pedro is working on implementing "Generic Defaults", as described in his Haskell Symposium 2010 paper www.dreixel.net/research/pdf/gdmh_nocolor.pdf It will replace (and improve on) the "Derivable type classes" stuff in GHC at the moment, which was originally presented in a paper of that title that Ralf and I wrote in the 2000 Haskell workshop http://research.microsoft.com/en-us/um/people/simonpj/papers/derive.htm. The "Derivable type class" extension is barely used, I believe, and isn't even documented in the manual. So I propose to switch from one to the other, rather than to try to support both. This change will happen in GHC 7.2 or 7.4, depending on when Pedro is done. Please yell if you are a secret user of derivable type classes, so this change would discombobulate you. Simon