functional dependencies

[Johannes Waldmann]

Can I write dependencies like this:
 
> class C x y z | x -> (y, z) 
> class D x y z | (x, y) -> z

in hugs? in ghc? The ghc doc refers to  
Mark Jones: "Type Classes with Functional Dependencies",
http://www.cse.ogi.edu/~mpj/pubs/fundeps.html
where this seems to be allowed (section 4, page 9)

Especially, I would need class D above. 
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