The Expression Problem strikes again!
There's a guy giving a good lecture on it: http://professor-fish.blogspot.com/2010/08/lecture-series-on... (I think he even has a solution in Haskell)
There's a guy giving a good lecture on it: http://professor-fish.blogspot.com/2010/08/lecture-series-on... (I think he even has a solution in Haskell)