type 'a voyel = ('a * 'a)

type 'a consonants =
  { ending : 'a option option
  ; opening : 'a list
  ; following : 'a option }

type 'a group = 'a voyel * 'a consonants option

type 'a modifier = (module Sounds.T with type t = 'a) -> ('a group * 'a option option)  -> ('a group * 'a option option)