let db = ref []

let to_list () =
  !db

let add_coercion c =
  db := c :: !db

let remove_coercion p = 
  db := List.filter (fun u -> not(p u)) !db

let find_coercion f =
  List.map (fun (_,_,x) -> x) (List.filter (fun (s,t,_) -> f (s,t)) !db)