(** The Nasal modifier transform a voyel followed by N and a consonant
    into a nasal voyel.

    Does this min that nasal voyel are not a distinct element, but just a
    merge from two distinct elements ? *)
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
    let ending = Option.bind ending (fun x -> x) in
    match ending with
    | None -> init
    | Some ending ->
      match T.is_nasal ending with
      | false -> init
      | true ->
        (* Remove the ending consonant, and transform the voyel into
           the nasal form  *)
        ( ( (T.nasal v1, T.nasal v2)
          , c )
        , None )