(** Transform the S into Z if the S is the opening consonant and
    there is no ending consonant before *)
let process
  : 'a Sig.modifier
  = fun (type el) m init ->
    let module T = (val m:Sounds.T with type t = el) in
    let (((v1, v2), c) , ending) = init in

    match c with
    | None -> init
    | Some op ->
      (* The voyel may be none in case of ending word. In such case, we shall
         not trnasform the S into Z *)
      let is_voyel = T.is_voyel v1 && T.is_voyel v2 in
      match is_voyel, op.Sig.opening, op.Sig.ending with
      | true, hd::[], None when T.code hd = T.SZ ->
        let c = Some { op with opening = [T.z ()] } in
        (((v1, v2), c) , ending)
      | _ -> init