module Hashtbl:Datatype.Hashtbl
with type key = t
include Hashtbl.S
val memo : 'a Datatype.t -> key -> (key -> 'a) -> 'a
memo tbl k f
returns the binding of k
in tbl
. If there is
no binding, add the binding f k
associated to k
in tbl
and return
it.module Key:Datatype.S
with type t = key
module Make: