[Haskell-cafe] All equations must have the same arity - why?

Hi, It's nice to write functions in point free style: f = sort . nub But sometimes I have to add an extra case, on a certain value: f [] = [1] f = sort . nub But now these equations have different arities, and its rejected by Haskell. Why does this not simply desugar to: f [] = [1] f x = (sort . nub) x i.e. lift the arities to the longest argument list. Is there a reason this isn't done? Thanks Neil