(* Environments *)

module type ENV = sig
  type 'a env
  val empty: 'a env
  val bind : string -> 'a -> 'a env -> 'a env
  val bindall : string list -> 'a list -> 'a env -> 'a env
  val make : string list -> 'a list -> 'a env 
  val lookup : string -> 'a env -> 'a option
end 

module Env : ENV = struct
  module T = Map.Make(String) (* String Tables *)
  type 'a env = 'a T.t
  let empty = T.empty
  let bind name valu env = T.add name valu env
  let bindall names vals env = List.fold_right2 bind names vals env
  let make names vals = bindall names vals empty
  let lookup name env = 
      (try 
         Some(T.find name env)
       with 
         Not_found -> None)
end