Date: Thu, 02 Jun 2005 10:29:03 -0400 People discussed the Map implementation in GHC: data Set a = Tip | Bin {-# UNPACK #-} !Size a !(Set a) !(Set a) type Size = Int ... I do not think that these strict fields can do a real harm, because they effect only a single level of data construction. And even if it was a strict language, operating with large sets would be all right. Still, I would prefer to remove `!' and UNPACK, in order to preserve a pure language. But what I really do not understand is: why not `Integer'? What difficulties may cause the design with size :: Set a -> Natural type Natural = Integer What will be the difference? With each insert envokation, recomputing size costs O(log n), the next call for size costs O(1). Right? Everything looks like for `Int' -- except that `Int' is a bug. "v :: Int" is a bug, if v can occur large. For example, we could imagine (there may appear, there may exist) a machine capable to process in a real time the number of cells much greater than maximal_Int. This depends on hardware architecture specifics. For such sets sS, size sS :: Int returns incorrect result. Regards, ----------------- Serge Mechveliani mechvel@botik.ru