adamc@469: functor Make(M : sig
adamc@469:                  type key
adamc@469:                  con id :: Name
adamc@469:                  con parent :: Name
adamc@469:                  con cols :: {Type}
adamc@469:                  constraint [id] ~ [parent]
adamc@469:                  constraint [id, parent] ~ cols
adamc@469: 
adamc@469:                  val key_inj : sql_injectable key
adamc@469:                  val option_key_inj : sql_injectable (option key)
adamc@469: 
adamc@469:                  table tab : [id = key, parent = option key] ++ cols
adamc@469:              end) : sig
adamc@469: 
adamc@469:     con id = M.id
adamc@469:     con parent = M.parent
adamc@469: 
adamc@469:     val tree : ($([id = M.key, parent = option M.key] ++ M.cols) -> xbody)
adamc@469:                -> option M.key
adamc@469:                -> transaction xbody
adamc@469: 
adamc@469: end