OCaml: type incompatibilities between sets -

i'm having troubles type incompatibilities in ocaml.

first, have file setbuilder.ml define functor creates order sets, functor s creates sets, , functor sm creates module containing useful functions work sets:

module (m: sig type t end)   = struct     type t = m.t     let compare = pervasives.compare   end  module s (p: sig type t end): set.s type elt = p.t   = set.make (so (p))  module sm (m: sig type t end):  sig   type t = m.t   module s: set.s type elt = t   type set = s.t   ... end = struct   module s = s (m)   ... end 

(in such situation i'm used combining such 3 modules 1 recursive module, appears ocaml doesn't let create recursive modules when parameter excepted (i.e., when it's functor)).

then in different file, called module_u.ml, define module u function foo important:

module u (m: sig type t end): sig   module s : set.s type elt = m.t   type elt = m.t   type eltset = s.t   val foo: eltset -> eltset -> bool end = struct    module s = s (m)   let foo s1 s2 =    ... end 

and in main.ml, define module containing type i'll using,

module t :  sig    type t=int end  = struct    type t=int end  

then instantiate module sm , obtain set s:

module sm = sm (t)   module intset = sm.s  

then instantiate module u , attempt use function foo:

module u = u (t) let bar (s1:intset.t) (s2:intset.t) : bool =    u.foo s1 s2 

but error message

file "main.ml", line 303, characters 38-39  (which corresponds s1, in u.foo s1 s2): error: expression has type intset.t = setbuilder.sm(t).s.t        expression expected of type          u.eltset = module_u.u(t).s.t 

what don't understand, why problem, since both u , sm modules created same module t, meaning type of 2 sets created should same.

if can provide thoughts on i'll thankful.

try using module s : module type of s(m), or alternatively module s : set.s type elt = m.t , type t = s(m).t. problem module s : set.s type elt = m.t doesn't constrain type s.t