Haskell: Sets

Given a finite Set type (not Data.Set), find a map Set -> Int that is bijective! (Let's try injective first, how would you do that?)

The definition of Set I have in mind is this:
data Set = Empty | Set [Set]
But if you want to use some other equivalent definition go ahead.

>>27
Alright, elaborate then please. As far as I understand it you're wrong.