Modules: type problem in functor

I have a type problem in the following code (some simple implementation of the module functional graph). Types seem to live their own lives.

I have type t = NotaEdge | Edge of int*v*v, implemented in the Edge module, this type in the Graph module becomes type edge = E.t. Everything seems fine to me, except for the fact that I cannot match it with a template, because the Edge constructor is still undefined in the Graph module.

Exactly in the su function, when I try to combine with Edge (l, n, m): #Error: Unbound constructor Edge

Hope someone can introduce it beautifully, thanks in advance :)

 module Vertex : Vertex with type label = int =

struct

  type t = NotaNode |  Node of int
  type label = int
  exception No of string

...

module Edge : Edge  with type label = int and type v = Vertex.t =
struct 

  type v = Vertex.t
  type t = NotaEdge | Edge of int*v*v
  type label = int      

  exception No of string

...

module Graph (E : Edge) (V : Vertex) : Graph with type vertex = V.t and type edge = E.t =
struct 

  type vertex = V.t
  type edge = E.t
  type t = E.t list* V.t list

  let empty = ([],[])

 let rec suc (x:edge list) (v1:vertex) =
     match x with 
         y::ys -> (match y with
   (*Error-->*)       Edge(l,n,m) -> if n == v1 then m::(suc ys v1) else suc ys v1  
                     | _ -> [])
       |[] -> []

  let succ (t1:t) (v1:vertex) = 
    match t1 with
        (x,_) -> suc x v1

...