I wish to add to Christian's question: why is it not possible to annotate v with its full type: info :: (Collects e ce, Show e) => ce -> String info (v::(Collects e ce, Show e) => ce) = show ((one v)::e) I then get the error message All of the type variables in the constraint `Collects e ce' are already in scope (at least one must be universally quantified here) In the type: (Collects e ce) => ce While checking a pattern type signature When checking the pattern: v :: forall. (Collects e ce) => ce In the definition of `info': info (v :: forall. (Collects e ce) => ce) = show ((one v) :: e) (and a similar message for the constraint Show e), which I do not understand - why should e and ce be already in scope? (I think that this question is actually independent of functional dependencies - it is about type class constraints). Till -- Till Mossakowski Phone +49-421-218-4683 Dept. of Computer Science Fax +49-421-218-3054 University of Bremen till@tzi.de P.O.Box 330440, D-28334 Bremen http://www.tzi.de/~till