Modules within classes

[Martin Hofmann <mhofmann@tcs.ifi.lmu.de>]

Dear all, 

Can someone explain what is wrong here and perhaps suggest a workaround? 

class ['a] test ( l : 'a list) = 
object 
   method result = 
     let module M = 
      struct
        type t = 'a      
        let compare x y =
          if x < y then -1 else if x > y then 1 else 0
      end
  in
    let module MSet = Set.Make(M)
    in  MSet.elements (List.fold_right MSet.add l MSet.empty) 
end;;

OCaml says: "Unbound type parameter 'a". 

Our aim is of course not to program sorting the umpteenth time but to 
have a means for using Pervasives.Set within a parametrised class.

The problem seems to be that although "class ['a]" binds 'a its use is 
nevertheless disallowed in the scope of the class declaration. 

Many thanks in advance!

Martin Hofmann (on behalf of Oliver Friedmann)